This is the antenna for you guys who want to get on HF effectively, and haven’t too much space or cash to throw around. Actually, it’s a design from ZS6BKW (aka G0GSF), similar to the G5RV, but it actually resonates on five bands, (well 6, actually) and doesn’t rely on a tuner (ATU) to make it work. The design appeared in TT (RadCom) Jan & Feb 1993, but is also in Pat Hawker’s “Antenna Topics” (publ. RSGB 2002) It’s only 90 ft long (27.51 metres), with a 40 ft (12.2 m) downlead.

So, it’s a cousin to the G5RV (which only resonates on 14 & 24 MHz), but better as it needs no ATU on 40, 20, 17, 12, 10 and 6 metres.

Horizontal or inverted V layout

When Telford DARS were doing the 50MHz Trophy contest down at Bridgnorth, I took the necessary bits along to try out this antenna. For simplicity, I set it up as an inverted-vee configuration. The reason was simple – you only need one support to hold it up, not two. I also had the club’s MFJ Antenna Analyser with me so that I could see what was happening. I recorded the data – see below.

Incidentally, all centre fed antennas can be supported by just one mast, with the ends left to droop down. The ‘rule of thumb’ is that the angle at the apex should never be less than 90 deg, otherwise cancellation between the two halves occurs. Furthermore, as it is the current peaks along an antenna that do most of the radiation, having the centre at the highest point is a positive advantage, rather than supported at each end with a big droop at the centre (current point nearest to ground). This is another reason for not being too fussy about the ends of a centre-fed antenna being lower, or bent around. It will have minimal effect on radiation efficiency. The only thing is never have the ends dropping right down to ground level – because the ground will seriously de-tune the antenna and it will not work – believe me, I’ve tried it. Just a yard or so off the deck makes all the difference. Simply have end insulators (or plastic strips etc), then wire or twine to the tying-off points. This effectively raises the ends of the antenna sufficiently clear of the ground. So, the ‘BKW can be horizontal (two supports) or inverted-vee layout (single support), as shown. Incidentally, the same applies to a simple dipole.

The antenna wire can be solid copper, stranded, insulated or not. A lot of rubbish is printed about the merits or otherwise of different sorts of wire. It’s largely hogwash. Wire is wire at these frequencies. Wet string ? …… well that’s a different matter….

In the original design, 300 ohm twin was used, but I prefer the 450 ohm stuff. It’s much stronger and losses, especially in wet weather, are lower when impedances are high down the line. Back in 1985, 450 twin wasn’t readily available, there was only 75 and 300 twin, or the option of making your own open-wire feeders (which actually are the best of all – around 600 ohm, but these do tend to twist or get caught in trees etc ! Yes – bitter experience and soldered joints here too !)

Finally, if you want to use it on other HF bands (3.5, 10, 21 MHz), an ATU (just like at the bottom of your ‘5RV !) will do the business, but preferably at the bottom of the 450 ohm feeder with a balanced output, not after a length of 50 ohm coax, if you’ve had to use it to reach your rig. Of course for 1.8 MHz (160m), you could short out the feeder twin, and feed it like a Marconi antenna, with a suitable ATU. Not very clever, however.

Here are the MFJ figures I recorded on the test antenna:-

Best in-band frequency:    SWR        “R” at feedpoint      notes:

 

3.38 MHz (80m)                                   7:1                          20                           tunes easily with ATU

7.00 MHz (40 m)                                  1:1                          40                           puurrfect

10.1 MHz (30 m)                                  high                        high                       needs atu

14.06 MHz (20 m)                               1:1                          40                           wonderful

17.85 MHz (17 m)                               1:1                          50                           below 1.3:1 in 18MHz band

21.00 MHz (15m)                                high                        high                        needs atu

24.69 MHz (12 m)                               2:1                          100                         OK, even without an ATU

28.62 MHz (10 m)                               1.3:1                       60                           No sweat!

50.27 MHz (6 m)                                  1.3:1                       60                           A surprise: 6m. too!

 

Just to show the “proof in the pudding”, I used it on 7 and 14 MHz, and got excellent reports, as one would expect with a half-decent antenna ! Didn’t have time to use it on all bands, but I leave that to you (to tell everyone how good it is….)

Article by Martyn Vincentv G3UKV

originally available at http://www.tdars.org/library/TechTopics/tech9.html

The post The ZS6BKW Multiband HF Antenna appeared first on IW5EDI Simone - Ham-Radio.

I was trying to increase the overall performance of the J-pole, in this design.  The diagram provided is a more simplified version of the one I did.  These are a few of the modifications I came up with.  I added a cap on the top end of the PVC.  Mounted a so-239 to a split piece of copper tubing, that took the place of the #14 copper wire.  And, I also added a short aluminum mast that fit into the lower end of the PVC.   I mounted the antenna to a 10′ antenna mast and a small tripod on the roof.  I tried to add some type of a ground plain but everything I did made the antenna perform poorly.  After all my efforts the end result was an antenna that out performs the 1/2-wave colinear copper version, with only one exception.  The working model is somewhat narrow banded and still requires more experimentation.  Some of the elements must be a little long.

Article originally available at http://home.comcast.net/~buck0/5-8thx2j.htm

The post 5/8 Collinear antenna appeared first on IW5EDI Simone - Ham-Radio.

Cubic Quads

KQ6RH

(C) 1998, 1999, 2000

Ray Jurgens

(Up-Dated 2/25/2000) 

  Cubic Quads

  The cubic quad is a very popular way to get reasonably high gain and excellent front to back ratios as well as low angles of radiation for without going to extreme heights. Here I present several designs that that achieve the great performance that hams have associated with this antenna for years. Data are presented for 2 and 6 meter quads and a combined 2 and 6 meter quad that is optimized. The 2 meter 3 element design gets a great 9.5 dBi gain coupled with a F/B ratio of 23 dB.

  Light weight portable cubic quads can be constructed rather easily from fiberglass tubes supported by central hubs. You should be familiar with the material presented in the Quad Loop and Pfeiffer Quad sections of the Antenna Magic page. Cubic quads for wavelengths shorter than 15 meters are easily constructed, however, you should be aware that the weight of these structures is larger by a factor of about 3 relative to most of the planar designs presented in the main menu. Because of this, a heavier mast must be used to support the structure in most cases. Also, be aware that the space needed to assemble and raise a full cubic quad is larger than for the planar designs, and this may be a significant limitation imposed in some locations. In my own case, the backyard associated with my town house is barely large enough to assemble a cubic quad with spreaders of 8′ in length. Wires and guy cords get tangled in the fruit trees, and spreaders hang over into neighbor’s yards. Anything larger 8′ with extended spreaders is essentially impossible to assemble without working above the level of the fence and fruit trees. For that reason, I shall present only two designs which are more or less typical of what can be done easily. The two designs presented are for HF and VHF and should be useful to a wide audience. The HF design is a two element quad for 10, 12, and 15 meters while the VHF design is a two element design for 6 meters with three elements for two meters. A specific advantage of the standard quad design is that multi-band operation is easily accommodated.

 

2 and 6 Meter Quad

  The spreader length necessary to support a 6 meter quad is less than 3.5 feet, so the standard 8′ lengths of fiberglass tubing can be cut in half to make 4′ sections. It is also possible to telescope shorter sections of 1/2″ and 1/4″ tubing to make a slightly lighter weight design. In that case, the 8′ sections could be cut in quarters and the overlap of about a half a foot would be entirely adequate for the telescoping leaving spreaders of about 3.5 feet. The boom length for a full quarter wave spacing is less than 4.75 feet, so a single 8′ piece of 1″ fiberglass tubing is more than ample.

  Looking quickly at the 2 meter requirements, the spreaders need be no longer than 1.25 feet and a three element wide spaced boom requires no more than 31.25″, thus this can be easily tucked between the 6 meter 2 element quad. In fact, it is necessary to stretch it out a bit. So, a common design requires beginning with an optimized design for 6 meters and accommodating the 2 meter design to the locations of its two hubs. The third 2 meter hub occupies a space between the two 6 meter hubs.

  Looking at an optimized 2-element 6-meter design, the following parameters give excellent performance:

  The 6 meter parameters are given in Table 2, which is a simple two element design:

  The next step is force the 2 meter 3 element quad to have a total boom length identical to that of the 6 meter quad. Note that the 2 meter 3 element easily fits within the same space as the 6 meter 2 element, that the 2 meter quad will have a longer boom than is considered optimum.

….

10, 12, and 15 Meter Quad

  The construction of 2 element cubic quads for 10, 12, and 15 meters is not very difficult, but the structure requires some guy strings to keep the light weight elements from bending. The bending actually would not degrade the performance very much, but the nice square structure clearly looks better, and it will probably hold up better under high winds. In order to keep the spreaders from bending due to gravity loading and wire loading, you will need to have a place to guy them from two directions. The antenna wires can serve as structural elements to help reduce the bending in the plane of the loops. However, bending is also a problem perpendicular to the plane of the loops, and guy strings are necessary to stabilize that direction as well. The easiest way to provide a place to connect the guys is to use a boom extension. The extension does not need to be any longer than 3 feet for 8′ spreaders. In the case of 15-meters, the boom can be about 8′, and the two extension increase the boom to 14′ or a turning radius of 7′. The actual turning radius of a quad depends upon whether it is set up as a diamond or square configuration, the square being the smaller of the two.

 Article originally available at http://www.antenna-magic.com/antenna/cubic_qu.htm

The post Notes on Cubic Quads appeared first on IW5EDI Simone - Ham-Radio.

This halo antenna by KB1DIG  is made with a true Gamma Section this time and is fashioned from aluminum.
Most of the parts are leftovers from old car projects. The best part is it’s omnidirectional!

The 3/8″ fuel-line I used came from Summit Racing Equipment: http://store.summitracing.com #SUM-G2538,
and a 25′ section costs only about $20.oo.

Frank NG1I and Steve N1TYH used aluminum fuel line from a NAPA auto parts supply store.

Welded the elements to the aluminum plate with some of that “Alumaloy” stuff advertised on television.

Alumaloy Sample auction  1/10 pound or 2 rods of alumaloy aluminum repair rods.
Go to eBay: http://www.ebay.com/  Key words for search: (SAMPLE) Aluminum REPAIR Rods ALUMALOY

I drilled a small hole in one of the elements to allow condensation to evaporate.

Capped off the end of the gamma arm with a plug to keep the weather out. The plug was an automotive type used to block off a PCV line from a carburetor.

After mounting horizontally to a 10′ mast I added a support system made from 2 thin 3′ fiberglass rods and some wire-ties.

Also, remember to hot-glue the wire-ties to the fiberglass rod.

Both 54″ elements are bolted and welded to the mounting plate.

Use galvanized or some other type of corrosion resistant bolts.

The size of the bolts is not so important other then that they fit snugly into the ends of the 3/8″ fule-line and hold the elements in place while welding the elements to the mounting plate.

This “Alumalloy” product is great for this purpose and is more like soldering than welding.

After the 2 elements are welded, leave the 2 bolts in place for added support.

The so-239 connector is pop-riveted to the mounting plate.  Face the pop-rivets out and away from the gamma section.

Cut back and expose about 1/4″ of the center conductor of the RG-8 section for soldering to so-239 connector.

Position the 1″ wide aluminum bracket on the Gamma arm, inward about 3 1/2″.

Expose about 3″ of the RG-8 coax center section.

This is just a starting point for matching this antenna.

I was lucky and didn’t need to make any further adjustment for lowering the SWR.  The SWR on this design seen here, just the way it is, was 1.2 to 1 at 50.125Mhz.

This halo design is intended to be mounted parallel to the ground.

It should work well for base or mobile operation.

I presently use this antenna at my home QTH and it has proven itself to be quite successful for SSB work.  It is presently up on the roof, mounted to a 10′ mast section in a 3′ tripod stand.

It can also be modified to work on the FM portion of the 6-meter band by shortening the length of the 2 main elements a little at a time.  I have not done this.  No change to the gamma arm will be required if this antenna is altered for 6-meter FM.

This article originally available at http://home.comcast.net/~buck0/6m_halo.htm

The post 6 Meter Halo Antenna Design appeared first on IW5EDI Simone - Ham-Radio.

 Dimensions of the 3 element Yagi antenna for 7 MHz

The post 40m 3 element Yagi appeared first on IW5EDI Simone - Ham-Radio.

Please feel free to build or distribute the information on these antennas. G4DHF retain the copyright to the designs and ask that they are not manufactured for commercial gain.

Introduction

This yagi is designed using highly flexible 16g plastic coated wire with an outer diameter of 3mm and a stranded inner conductor of 1.5mm and is of the type readily available from most electrical retailers. The plastic coating has a significant effect on the resonant length of the elements due to changes in the velocity factor when compared to free space values. The value of the velocity factor was determined by trail and error over a period of many weeks and several yagis. A correction factor of around 7% to 5% from the free space values gave repeatedly good results and a value of 5% has been applied in this design. If a different wire diameter is used or the wire is non-insulated changes to the length of each element will be required to compensate. As the elements are very thin it was expected that the operating bandwidth would be limited to around a few hundred kHz at 144MHz. As the operating frequency was designed around 144.1 MHz this should be of little concern to those operating in the European DX section of the band. In fact, the beam will give creditable performance up to around 144.6 MHz after which the 50 ohm feed impedance, gain and front to back ratio rapidly begins to deteriorate.

Cut the element lengths to these dimensions

Cord Framework

The elements are held in position along a string frame, supported by four 6mm fibre spreaders. A number of string types were tried, ranging from 1.5mm polypropylene line to the more conventional household twine. Almost all exhibited an unacceptable memory affect, which turned the beam into tangled wire when the supports were removed. The ideal material was found during a visit to a kite shop when 2mm flying line was purchased. This consists of hundreds of fine nylon strands bound together in a woven cotton outer sheath. This cord is highly resilient to stretching, has minimal memory affect and is extremely strong. Once used there was no going back to the types used in the prototypes.

Securing the Elements

The end of each element is secured into lengths of 5mm plastic hollow tubing, obtained from model and craft shops. Each element end support has a different length in order to preserve the shape of the supporting frame. After the tips have been drilled each element is threaded along the length of the cord to their correct position. The end of each element is at a high RF voltage potential so care needs to be taken to ensure that surrounding objects and materials due not exhibit detuning effects. Four small lengths of 2mm plastic rod terminate each of the supporting frame by providing tie points for the cord.

Element End Support Dimensions

Driven Element

The Driven Element consists of a simple dipole. The feed impedance for a conventional yagi is usually considerably lower than the desired 50 ohm feed and requires some form of matching network to compensate. This design sacrifices a few tenths of a dB of forward gain so that by careful attention to the length and position of the first director in relation to the dipole the feed impedance is raised to the desired value. This concept is not new. Indeed, at least one well-known commercial manufacturer of V/UHF antennas has used this technique successfully over many years, including matching UHF folded dipoles directly with 50 ohm cable. These parameters are, however, quite critical and so careful attention should be given to ensuring that the recommended dimensions are followed. The centre of the dipole passes through a small plastic support and is terminated with standard spade connectors, as weight at this point needs to be kept as light a possible to reduce element sag. The dipole requires an unbalanced to balanced balun, which is described below.

Unbalanced to Balanced Coaxial Balun

This balun serves to provide an unbalanced to balanced 50 ohm match, which helps reduce RF currents on the outer of the feed. Omit this balun at your peril as the antenna may exhibit false resonance at the desired frequency or high SWR due to the presence of circulating currents. For RG-58U coax with a velocity factor of 0.66, cut a 34cm length and trim back the braid 5mm at en end. Note that the two lengths run parallel to each other and that the braid and inner are isolated at opposite ends.

Construction

The end of each element is cut to the corrected length and secured into plastic element spacers, which are drilled 5mm from the tip and threaded onto the two outer lengths of kite cord. The element positions are marked out onto a length of wood and the cord stretched between two sets of panel pins. Thread one end of the Reflector element first, followed by the plastic end cap that holds the fibre support. When the beam is assembled these caps hold the Reflector and 2nd Director tight against the end supports. Next thread the Driven element, Director 1, another end cap and finally Director 2. Repeat the process for the opposite side. When the fibre supports are inserted into the end caps the beam assumes it’s physical dimensions. The element ends can be glued along the cord, but leave Director 1 free until adjustments are complete.

Fibre Supports

The shape of the yagi is created when the four fibre supports are inserted into a central hub and the four plastic end caps at each corner of the beam. Lengths of 6mm fibre rod are available from a DIY stores and kite retailers. I have even successfully used the types that support bicycle flags. The total length of each support is around 865cm, which I cut into three sections for portability. There is an additional 4cm of “hidden” length to be added when they are fitted into the central hub. I placed small lengths of 8mm (6mm ID) aluminium tubing on each end of all the second sections to enable the rods to be compression fitted together. A word of caution is necessary when handling and cutting these rods as fibres can easily become embedded in the skin causing irritation so gloves must be worn. When the rods have been cut each end should be dipped in “Super Glue” to prevent the fibres from peeling. Furthermore, the addition of heat shrink sleeving makes for safer handling. It is not recommended to use wooden dowel for the supports as the tension required to form the structure is quite high and this will either distort or snap the wood.

Supporting Hub and Mast Connection

This yagi has to be lightweight, strong and portable. Metal fixings are almost eliminated. The supporting plates consist of two 9cm x 7cm sheets of 3mm acrylic. The geometry of the structure is scored on one of the sheets to determine the centre. Mark the 67-degree angle created by the fibre supports. The sheets are held together with the markings on top so the centre-supporting hole can be drilled. If two stacked antennas are planned, supported by a 6 metre to 9 metre fibre pole, the top antenna has a hole diameter of 2.5cm while the second, located some two metres lower has a cut out of 3.5cm. The four 4cm lengths of 8mm aluminium tube that house the fibre spreaders are then pop riveted in place. Turn the support over and secure the reverse. Two small “L” shaped aluminium brackets (or square open section) are formed and secured either side of the plates. These support a length of ribbed rubber matting, which, with the additional of cable ties, increases the grip between the central support and the mast support. There may be concerns regarding the effect of sunlight on acrylic over time but because the yagi is intended for temporary use the trade off in weight, strength and ease of assembly more than compensates for this potential problem.

Alignment

Attach the antenna to an insulated mast at a comfortable working height of between five to six feet above ground in a clear environment. Attach the ends of the coaxial balun to the Driven Element and connect a length of 50 ohm cable to either an antenna analyser or SWR meter connected to a low level (1 watt max) 2 Metre signal source. Note the impedance or amount of reflected power. If the dimensions of the beam have been followed closely these will be reasonably low and close to 50 ohm. Moving only the position of the first director in 2mm steps, usually towards the Driven Element, note the change in impedance until the desired match is achieved. The antenna can now be raised to a more suitable operating height to confirm alignment. When complete, the position of D1 is marked and secured. Lengths of lightweight plastic placed either side of the dipole centre help to maintain this distance, which is critical, when the elements sag slightly in operation. Once aligned and the distance between D1 and the Driven Element has been secured power levels of up to 300W have been used successfully.

Stacking Antennas

As has been previously suggested, stacking two or more of these beams is perfectly viable due to their low weight. Stacking two antennas at a distance of one wavelength (6′) should yield a forward gain of about 11dBD, which makes for quite a potent one-person system.

Results

Readers may be interested to know just how effectively this type of antenna can perform. While testing one of the prototypes in the garden of my QTH near Spalding (IO92UU) in May 2005 we had a Sporadic “E” event late in the afternoon. I worked CN8LI (IM63) at a distance of 2163Km, EA9IB (IM85) 1966Km and several EA7’s running only 20W. Given the high QRM levels and the number of G stations who were active, these results speak for themselves and should encourage potential builders to “get busy”. I would be interested in receiving comments and details of your operating experiences using this type of antenna.

Author G4DHF

The post Ultra-portable 5ele 144MHz Pocket Portable Yagi appeared first on IW5EDI Simone - Ham-Radio.

There are quite a few ways to make full-sized dipoles that can be rotated.

How you attack this mostly depends upon what band is to be covered (basically how big) and whether the wire is to be horizontal or is permitted to slope downward from a central post.

In the horizontal case, the wire is threaded through the spreaders and may extend out the ends. The ¼” tubes have an adequate ID that #16 wire is easily passed through the tube, so extenders can be added to the usual fiberglass ½” tubes that fit the hub.

In doing this, you should be aware that the velocity factor will be less than unity, so the physical size of the dipole will be slightly smaller than that of free space. In order to make connections to the feed line at the hub, two ¼” diameter holes have to be drilled at an outward slant into two opposite spreader sockets.

These should be drilled at about a 45 degree slant beginning about ½” out from the center. A ten meter dipole requires no extenders. Longer wavelengths require extenders, and the 20 meter dipole may require wire extending slightly beyond the extended spreaders.

In general, feed the wire through the extender first, then into the ½” tubing, then slide the extender into the half inch tubing and push the wire beyond the end of the spreader about 4″. Feed the wire into the hub and up through the access holes that you drilled. Then push the spreader into the hub.

Now, from the tip of the spreader pull the wire until there remains just enough wire at the hub to make the connections to the feeder. Adjust the length of the spreader extenders, and tighten the hose clamps.

Leave about a foot of extra wire beyond the extender. You will then need to trim this to get proper resonance once the structure is in the air. In the case of ten meters, you are done, simply mount the hub on the mast and put it up. No guy lines are needed if you don’t mind a bit of droop. In the case of 20 meters, there is much more to do. Here, the length of the spreader will be about 15′ if you have a 1′ overlap with the extender.

So you will need a central guy post 6′ long, i.e., use a full 8′ section of 1″ tubing with 2′ below the hub. You will need guys to both the inner spreader at 8′ and the outer extender at 15′ up to the central hub for both spreaders. You also may need rotational stability if you want this to settle down after rotation or gusts of wind.

The two unused socket holes are there for a reason, so, fit two 6′ or 8′ (if you have room) ½” spreaders in these sockets and guy them in the same manner as before at the 8′ and 15′ locations. Always set the guys from the inside first, then add the outer ones. This is still a fairly loose structure since only gravity holds it in the downward direction. If this structure is still not stiff enough, you can guy downward to the mast as well. The limiting tension is set by the point where the extenders begin to buckle. That turns out not to be a whole lot of tension, because a 7′ section of the ¼” tubing sets the limit.

The second procedure is to make an inverted V dipole, where the antenna is the upper guy lines from the center pole out to the spreader tips.

For the ten meter case, this is nearly identical to the ground/counterpoise discussed in the Quick Vertical section. In that case, there are no extenders, so the construction is very simple. In the 20 meter case, all the same problems are encountered as above except that the wire load is acting as the upper guy lines rather than being in the spreaders. We also suggest using light wire for the 20 meter version. In fact, # 18 or # 20 hook-up wire works well, and the insulation should be left on.

We prefer the un-tinned type that is commonly available at Radio Shack. Using, the 6′ center pole, the length to the tip should be just about correct, however, the insulation slightly reduces the velocity factor, so you can shorten the extender or use a small length of Nylon fish line to extend the wire.

Note, the 17 and 20 meter versions of these dipoles are fairly large structures and can not be built up in small spaces. They are also rather flimsy, and go through lots of distortion when being tipped up. These are better erected from a push-up mast with the rotator near the top of the mast. This Dipole antenna gives the same gain as all other dipoles, however, the Half Square is a much better DX antenna for a given elevation and may be worth the extra effort. All parts used for the construction of the dipole can be used to construct the Half Square, so there is no loss in investment if you decide to switch. Note that 6 and 10 meters require no extenders, but we do recommend that you use guys from the tips to the center post. The post should extend about 3′ above the hub.

Parts required for all 6 and 10 meters versions:

Extenders are required for 12 , 15, and 20 meters.

To determine how much 1/4″ fiberglass to buy, you need to calculate the approximate length required for the dipole. If the wire is to be inside the fiberglass, the velocity factor is slightly less than 90%.

The size of a typical dipole is given approximately by 468/fMHz. This formula has a small correction factor for finite wire diameter and end effects.

When the wire is inside the fiberglass tubing, the appropriate factor is about 435/fMHz, so the lengths of the spreaders require for 12, 15, 17, and 20 meters is roughly as 8.72′, 10.25′, 12.02′, and 15.33′.

Assuming 6″ overlap and 8′ lengths of 1/2″ OD spreaders, the extenders will have to be 1.22′, 2.75′, 4.52′, and 7.83′.

Obviously, there is no compelling reason to cut the 8′ of 1/4″ OD tubing for the 20 meter spreaders.

You can get both a 15 and 17 meter extender our of a single 8′ length of tubing. 15, 17 and 20 meters require lateral guys to increase the stability. This requires two 4′ lengths of 1/2″ OD tubing inserted in the two remaining sockets.

Guys should be run to the tips of both the 8′ dipole tips and the extended tips. This is also true from the central Guy post. The guys can be either 50 lb. test Nylon fishing line or Kevlar thread.

The photos associated with the Half Square antenna show structures built with both fiberglass and PVC.

Article by KQ6RH

originally available at http://www.antenna-magic.com/antenna/dipole.htm

The post Rotatable Dipoles appeared first on IW5EDI Simone - Ham-Radio.

I have been getting into software defined radio via RTLSDR and found the stock antennas woeful for reception and picked up a tonne of noise from my LCD and laptop – though it’s hardly surprising.  So to improve the situation and spend as little as possible I decided to make a discone antenna. 

After some research I happened upon VE3SQB’s site and a neat discone design program for Windows.

As a compromise between frequency and unwieldyness I settled on 130MHz as the lower bound.  Discones are inherently wideband and I expect the antenna to be useful for reception in the 60MHz to 1700MHz band the E4000 tuner can work with.

The ingredients, all from Bunnings are:

• 1m of40mm PVC pipe (my lust for PVC in making antennas is unabated)
• 2.5mm galvanised tie wire
• A 40mm endcap
• Some masonite packer
• 1.5cm brass washers
• Stripped solid core ethernet cable

From Middy’s Electrical Wholesaler I bought:

• 20m RG6 quadshield coax cable
• A bunch of F crimp type connectors (just crimped them with my pliers)
• F to TV/Belling-Lee adapter

With no test gear I have no idea what the true parameters of the antenna are.  All I can say that it has massively improved the reception on my EzyTV dongle for VHF and UHF transmissions in conjuction with placing the antenna in the far end of my backyard.  I can also see distant ADS-B blips in HDSDR which I will get around to tuning into on GNURadio.

So go forth and make your own discone!

Download the Discone Notes file

Link originally available here http://helix.air.net.au

The post Discone Antenna for RTL SDR appeared first on IW5EDI Simone - Ham-Radio.

The frequency scaling formulas for Cubical Quad antennas are shown in this picture.

Note that frequency is measured in Megahertz {MHz} and the total length of each element is measured in feet {ft}.

The spacing of each element is the same and all directors are the same size.

The gamma match uses a small air variable capacitor approximately the value given and an adjustable shorting bar at the end connected to the element. The antenna is tuned by adjusting the length of the shorting bar on the gamma match for minimum VSWR with the variable capacitor half engaged. Then adjust the capacitor for minimum VSWR at the mid band frequency.

The enclosed EXCEL programs:  CubQuad.zip (includes cubicalq.xls, cubquad2.xls, cubqvswr.xls) can be used to determine the element lengths and the gamma match values for different frequencies.

In general the design is robust and may be optimized for gain or front to back by adjusting the spacing of the elements.

Figure 1. Cubical Quad Frequency Scaling Equations.

This antenna design has been built for both the ten and two meter versions and I have used them for T-Hunting and in two CVARC Field Day events with good results.

Figures 2 and 3 show the calculated antenna patterns and performance.

Table 1 shows an example output from the EXCEL Scaling program.

Figure 4. Shows VSWR vs. Frequency for three different 2 meter antennas, a 4 element Quad, a 6 and a 12 element Yagi.

Figure 2. Elevation Pattern for the 4 element Cubical Quad 36″ above a perfect ground

Figure 3. Azimuth Pattern for the 4 element Cubical Quad 36″ above a perfect ground

Figure 4. VSWR vs. Frequency for Three 2 Meter Antenna Designs.

Table 1. Cubical Quad Scaling Relationships

The post Cubical Quad Design appeared first on IW5EDI Simone - Ham-Radio.

I decided to publish this website in order to pass on some insights about this antenna that I’ve garnered through extensive experimentation. A warning though, some of the combined design aspects of the antenna may be unique and unorthodox, a think out of the box antenna design. Note! I do not have a B.S. or M.S. in EE, which makes me a true “amateur” amateur radio operator not a “professional” amateur radio operator, so some of my antenna theory explanations may be incorrect.

I have gained DXCC on 160 meters with 145 confirmed as of October 1, 2005, using this antenna design, in approximately 4 years. 25% of the DXCC contacts were via CW and 75% via phone. 103 DXCC contacts were with 140 watts PEP, 17 with 800 watts PEP.

What I have done is to simply identify the basic inherent weaknesses of the average 1/4 acre city lot 1/4 wave inverted L with a 30-50 foot vertical section and a few 1/4-1/8 wavelength radials and have devised methods to overcome these weaknesses. This antenna design is not meant to be a rival to a 4 square vertical array but can compete with a full 1/4 wave vertical with 60 1/4 wave ground mounted or buried radial wires, if designed correctly.

First of all let me say that I’m not a professional broadcast radio engineer. My background is in the sciences, i.e., climatology, meteorology, oceanography and space plasma physics. I’m just a true amateur experimenter, antenna modeler and voracious reader of every book on antenna theory and design that I have been able to get my hands on, some 50 years old. As an avid antenna experimenter, I have spent approximately 10 years in the field experimenting with this antenna design and it’s variants (1/4, 3/8, 1/2 wave L/Tee Vertical), between 1993 and 2002 and have also done extensive modeling using EZNEC 5.0. My good friend K4TR Joe Dube of Brooksville, FL has also been experimenting with this design between 1997-2002.

Along the way I have come to the conclusion that some of present day antenna theory is just that theory, in general concepts not totally proven by controlled scientific experiment and/or overemphasized and therefore to be taken with a grain of salt in some instances! I have also concluded that allot of sound basic antenna theory and design has been lost to time and/or watered down, to the point that many Amateur Radio Operators are now grossly miss informed about the basics.

A Broadcast Radio Engineer may come along and poke holes in some of the following antenna theory and concepts, as I’ve explained them. I have been told repeatedly that I know nothing about antenna’s. Even if the theory of operation of the linear loaded voltage fed Tee Vertical as I explain it is flawed in any way, one thing that can’t be disputed is that the antenna is a proven performer.

The average city lot backyard 1/4 wave inverted L suffers from several inherent weaknesses to include high vertically polarized local noise pickup, absorption and pattern distortion of radiated signal due to surrounding ground clutter, high capacitive coupling signal loss between the antenna and the average backyard poorly conducting soil conditions, to include an inferior ground radial system and low radiation resistance, a measure of antenna efficiency, due to the typically short (30-50 feet) vertical radiating element section of a 1/4 wave inverted L.

The proper definition of radiation resistance is; the total power radiated as an electromagnetic radiation, divided by the square of the current at some defined point in the system. To put it in simplest terms, a measure of antenna transmitted signal efficiency.

A 1/4 wave radiator will focus it’s current field in the ground immediately around it’s feed point and as you extend the vertical section past 1/4 wave, the highest current point moves up the vertical section and outward on and in the ground surface. With much effort the near field transmitted signal losses can be reduced to a point that you improve antenna efficiency to maybe around 50-75%. However the average backyard 1/4 acre location makes it difficult to overcome signal losses in the mid field (200-500 feet) on 160 meters and signal losses in the far field (between 500 and 1000 feet for a 1/4 wave vertical and around 52,000 feet for a true 1/2 wave L/Tee Vertical) (Fresnel Zone) is out of reach for all of us.

The linear loaded voltage fed Tee Vertical antenna places the highest current point at or near the top of the support structure gaining the following advantages. The elevated highest current point of the antenna is above allot of the local vertically polarized noise field. At my QTH my 1/4 wave inverted L noise level was always S9 to +5 over. With my linear loaded voltage fed Tee Vertical, the noise level has been reduced to S1-2. Of course the actual amount of noise reduction will vary from QTH to QTH. Another advantage of elevating the highest current point is, reduced radiated signal absorption and pattern distortion, away from omni-directional. In a sense you can say that the highest current point is getting a better omni-directional look at the radio horizon. Actually though it’s best to have the highest current point say approximately 25-50% below the flat top to assure vertical polarization. Remember the linear loaded voltage fed Tee Vertical is a DX antenna with a null overhead and therefore little high angle radiation close in for rag chewing.

Another advantage of elevating the highest current point, per the ARRL Antenna Handbook edition #15, is the reduction of capacitively coupled transmitted signal loss between antenna and lossy ground. Logic dictates that placing distance between the highest current point of the antenna and lossy ground possibly reduces capacitive coupling losses in the near field. Of course though due to the wavelength involved, the reduction in loss will be not the same on 160 meters versus say 40-10 meters.

The agreed upon standard for the number of ground radials for least near field loss for a 1/4 vertical antenna is 120 1/2 waves but you see a diminishing point of return after approximately 24 1/8 wave or 16 1/4 wave radials and there is virtually no difference (approximately 0.07 db) between 50-60 1/4 waves and 110-120 1/2 waves. Also basically your ground radials need not be any longer then the length of the vertical section of your antenna. An alternative to ground radials is an elevated counterpoise, which will be covered further into the text.

Radiation resistance, which as stated previously is a measure of transmitting antenna efficiency, is obviously a very important but difficult to accurately measure variable, basically the higher the value the better. Once again the proper definition of radiation resistance is; the total power radiated as an electromagnetic radiation, divided by the square of the current at some defined point in the system.

A 1/4 wave inverted L with a vertical section of 50 feet, will have a very low radiation resistance, around 15 ohms (very inefficient), increasing to near a theoretical 36 ohms as you approach a vertical length of 1/4 wave. Take this 15 ohms of radiation resistance and couple it with a poor ground radial system say 50% efficiency at best and you still have a very inefficient signal radiator. By the way, if you feed a 1/4 wave vertical at one end then the feed point impedance becomes the same as radiation resistance. However bend the radiator like an inverted L and the two are no longer the same.

Another method used to improve radiation resistance is to employ a capacity hat top loading system. A traditional capacity hat in the form of at least three flat top or sloping wires spaced approximately 120 deg apart and tied together at their ends in a ring shape, is employed to make up for the missing part of a short vertical antenna. Basically each top hat wire length should be at least the same length as the missing part of the vertical. On 160 meters an 1/8 wave vertical with an approximate length of 64 feet should have a three top hat wire lengths of 64 feet. This method of top hat loading increases the radiation resistance of the short vertical, (much like a linear load which is normally placed at the bottom of the vertical) only even better and moves the highest current point up the vertical portion of the antenna. The highest current point on my voltage fed Tee Vertical is elevated approximately 60 feet above ground using this method. If at all possible mount the top loading wires as high on the ends as in the center because dropping the wire ends effectively shortens the vertical section of the antenna. At my QTH the best I can do is to get the ends of the top loading wires 70 feet above ground versus 80 feet at center.

There are several methods that can be employed to reduce near field ground losses and in some cases increase radiation resistance and henceforth transmitting antenna efficiency, excluding the laying out of dozens of ground radials. One is to place 3-4 ground radial wires into an above ground counterpoise system (for a typical backyard 1/4 wave inverted L antenna). Four 1/4 wave wires approximately 15-30 feet off the ground, can rival 120 1/2 wave radials on the ground, as far as connection losses (which can 10-40 db) and lowest takeoff angle but not necessarily concerning near field ground losses (which has been measured at approximately up to approximately 5 db by W8JI). Unfortunately though raising radial wires into an elevated counterpoise also effectively shortens the vertical section of the antenna, similar to top loading wires.

It would seem logical that the linear loaded voltage fed Tee Vertical antenna would require a less extensive ground radial or counterpoise system in the near field at the antenna feed point, as the antenna is much longer than a 1/4 wave and has the highest current point elevated well above the ground surface and also well away from the feed point on the ground surface. However there will still be “some” losses in this nearer field but just further out from the antenna feed point. The problem though is that it’s difficult to get enough wire in the ground to overcome the ground losses at the further distance, on a typical 1/4 acre suburban lot.

Another method is to lengthen the transmitting antenna. As mentioned earlier, in theory the radiation resistance measured at the end feed point of a 50 foot vertical section inverted L is around 15 ohms, a linear loaded 1/4 wave L is near 16 ohms, a full 1/4 wave vertical is 36 ohms, a full 3/8 wave vertical is 300 ohms and a full 1/2 wave vertical is 1000+ ohms, a very efficient figure indeed! Basically as you lengthen the radiating element the radiation resistance increases and it decreases as you shorten it, it also varies with the diameter of the radiator. Antenna input impedance varies according to where you feed it. The added length of the antenna can be placed in a linear load configuration.

As mentioned earlier, the average backyard 1/4 acre location makes it difficult to overcome signal losses further out in the near field (maximum concentrated ground current is approximately 3/8 wave length out from the feed point with a 1/2 wave vertical) on 160 meters. Reducing signal losses in the far field at the first reflection point (Fresnel Zone), which is around 52,000 feet for a true 1/2 wave vertical, is completely out of reach for all of us.

To recap the various methods of improving antenna efficiency and performance; lengthen the antenna past 1/4 wave using a linear load, add a capacity hat in the form of a three wire flat top, elevate the highest current point, use a radial counterpoise system.

So that’s it in a nutshell, the linear loaded voltage fed Tee Vertical can overcome most all the inherent weaknesses of the “average 1/4 acre city lot” backyard 1/4 wave inverted L.

Now let’s discuss the benefits of using the linear loaded voltage fed Tee Vertical on 80 through 10 meters, as a multi-band antenna. As the length of a transmitting antenna exceeds a full wave on the operating frequency interesting things begin to happen. Gain starts to increase and the radiation moves inward towards the axis of the transmitting wire, versus the 90 degree broadside you see on a half wave dipole at 1/2 wave height. As the transmitting antenna continues to become even longer in comparison to the operating frequency, multiple lobes of radiation form on the wire in response to the numerous highest current points that exist.

Using the Tee Vertical antenna as a multi-band antenna on 80-10 I’ve had very good results. On 17 meters I have worked 100 DXCC countries with minimal time and effort.

It is strongly recommended that a high voltage handling parallel network matching device be used to load up the linear loaded voltage fed Tee Vertical antenna. Also as a tuner will see at least 1,000 ohms of feed point impedance on 160 meters with a linear loaded voltage fed Tee Vertical, your average store bought Tee network tuner can’t deal with such a high impedance and voltage. My matcher is a parallel network consisting of high power components, one 700 pf split stator 5 kw variable capacitor and a 28uh 5 kw roller inductor.

It is also recommended that the parallel network tuner at the antenna end feed point be fed with a high quality run of Belden 9913/RG-8U or Belden 9258/RG-8X coax back to the radio shack. For 80 through 10 meter operation, it is recommended that you use 450/600 ohm ladder line from the antenna end feed point, to a “balanced” network tuner just inside of the shack.

Attaching one 1/4 wave radial for 80 through 10 meters, to the ground side of the tuner and tuning the radials for maximum current with say the MFJ-931 Artificial Ground removes 100% of any stray RFI in the shack to zero. I have found a minor amount of shack RFI on 40 through 10 meters using the linear loaded voltage fed Tee Vertical but have gotten rid of it easily using the above mentioned method. Also making up some stub lengths of wire that make the total length of the antenna on each band of operation an odd quarter wave multiple, moves the first highest current point at the matching network and removes all shack RF.

I’m constantly experimenting with different radiator lengths and layouts. As of 10/01/02 my configuration of the linear loaded voltage fed Tee Vertical/Doublet antenna is:

A linear loaded voltage fed Tee Vertical antenna with the entire vertical section and linear load section made out of 450 ohm ladder line. The vertical section is 80 feet high, with a 47 foot linear load horizontal section one foot above ground that terminates in the tuning doghouse, to a legal limit plus rated home brew parallel matching network and driven against one 1/4 wave radial on the ground, four 10 foot long ground rods and a 150 foot deep well casing. The capacity hat is comprised of three 144 foot wires using #12 stranded wire, spaced one foot apart and sloping down to 70 feet.

Of course the ground rods and well casing don’t do much if anything as far as reducing near field ground losses and are actually part of my DC lightning ground. My ground system is sitting over very wet and highly conductive muck soil with swamp and ponds in the near field and Fresnel zone of the antenna. I also have a near zero local QRN level even on the transmit antenna, lucky me!

I’ve also had similar good performance with a voltage fed Tee Vertical using three 200 foot capacity hat wires, a 52 foot vertical section, a 75 foot horizontal linear load one foot above ground, with nine 1/8 wave counterpoise wires 5 feet above ground.

Per the EZNEC 5.0 modeling program, my 80 foot Tee Vertical has a near perfect textbook circle radiation pattern, with 1.95 dbi gain at a takeoff angle of 20 degrees, a 3 db beam width of 51.2 degrees, F/B of 0.30 db, feed point impedance of 628.6-j19350, a 1 mile mV/m of 134.22 using 1000 watts, with the highest current point elevated at approximately 60 feet above ground. However for all intents and purposes the highest current is nearly equally distributed along the 80 foot vertical section thanks to the capacity top hat and 47 foot linear load horizontal section one foot above ground. See links below for model diagrams of the Tee Vertical antenna.

If you zig zag sections of wire, that can’t be placed in a vertical position, versus using a coil, it’s much more efficient then a coil and radiates to a certain extent. Actually, if the linear loaded sections are designed right, they can add to the current on the vertical section, of a 1/4 wave L. It’s an idea I borrowed from VE3DO and discussed in ON4UN’s book “Low Band DXing”.

Remember once again, the linear loaded voltage fed Tee Vertical is a DX antenna with a null overhead and therefore virtually no high angle radiation close in for rag chewing. Put your linear loaded voltage fed T antenna on a pulley and you can lower it at will, roll up one leg (100 feet) of the 200 foot flat top into a ball or place an isolation relay to electrically remove one leg, the antenna then becomes and inverted L electrically and performance wise.

However thanks to the creative ingenuity of Joe Dube, K4TR of Brooksville, FL., who owns D & G Antennas there is another option. Joe came up with the idea of turning our linear loaded voltage fed Tee Vertical into a ladder line fed all band doublet/dipole. By flipping a switch which actuates a SPDT 12 volt relay at the antenna feed point in the dog house, the Tee Vertical becomes a 160-10 meter horizontal doublet with lot’s of gain.
K4TR D&G ANTENNA MFG & SALES

At times due to the nature of propagation on 160 meters during propagation disturbances, a low dipole can outperform a Tee Vertical on DX and is also quieter. I also have the added benefit of switching to the regional big signal cloud warmer low noise dipole to overcome high summertime lightning induced QRN for rag chewing. I use the dipole antenna set up in conjunction with a good performing Time wave DSP-9+ for summer operation. Click on the link below to see a diagram of the remote relay switching arrangement.

Having field tested the K4TR’s doublet aspect of the antenna design on 80-10 meters during the summer of 2002 I can verify that it works very well as and all band rag chew and DX antenna. I use a homebrew Tee network matching box to tune out inductive reactance.

Also last but not least, a personal observation concerning short monopoles. When I model a 52 foot vertical with one 200 foot top hat wire using EZNEC 3.0 on 1830 kc, then add two more 200 foot top hat wires, the near electric field in V/m RMS increases, the total electric field at 1 mile increases and the feed point impedance increases a little. When I conduct the same modeling exercise on 180 kc I see the same results as at 1830 kc but cannot verify it in the field. With no top hat wires attached a 52 foot vertical antenna obviously has capacitive reactance and therefore inductive top loading wires are needed or a linear load or at a last resort a lossy coil. With the 52 foot vertical and three 200 foot top hat wires the antenna feed point becomes inductive and feed point impedance high enough for the necessity of a parallel matching network. When you feed a 90 degree monopole at it’s ground end the feed point impedance and radiation resistance are basically synonymous, lengthen the monopole to 135 or 180 deg and of course feed point impedance and radiation resistance become different but the added “electrical” length does seem to increase radiation resistance.

I’ve done extensive experimentation with radials on vertical antennas on 160 meters during the past 18 years.

Back in 2001 a MF broadcast engineer friend of mine using professional broadcast measuring equipment, took near field measurements of the electric field in V/m RMS. The antenna was a 1/4 wave inverted L with a 64 foot vertical section and (1/8 wave) 64 foot long radials laying on the ground surface.

I found the following:

There was little measurable difference between 0 and 4 radials, a small measurable difference between 4 and 8 radials, a medium measurable difference between 8-16 radials, a large measurable difference between 16 and 32 radials, a small measurable difference between 32 and 64 and no discernable measurable difference between 64 and 120 radials.

We then conducted another experiment using conventional (1/4 wave) 128 foot radials and found the data to be exactly the same as the 1/8 wave radials. To me this proved the theory that the radials need not be any longer than the vertical section is tall.

I have never had the opportunity to do the experiment with a full 1/4 wave vertical.

This statement will be controversial. Using a voltage fed electrical 1/2 wave tee antenna with a 64 foot vertical section and three 200 foot long top hat wires, in the near field we measured only a very small difference between 1 radial and 64 1/8 wave radials. We measured no difference between 1 radial and 64 1/4 wave radials.

The ground conductivity was pretty good at the location of the experiment. It was a typical Florida hammock swamp that had been filled in but always had black mucky soil and a high water table. The conductivity was approximately .03 S/M with a dielectric constant of approximately 20. I’ve always presumed that the results might be different over ground with poor conductivity.

Here are some modeling results for the linear loaded voltage fed Tee Vertical antenna using EZNEC 5.0. Click on the links below to see the results. Link #1 shows current distribution which is very similar along the length of the 80 foot vertical section but peaks at approximately 60 feet up, link #2 shows takeoff angle and total pattern.

article by W4HM originally available at http://www.wcflunatall.com/w4hm9.htm

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Buddipole vs Dipole

Today during our Club annual  “Filetto Day” , a parody event of the famous ARRL Field Day,  I’ve been able to compare my Buddipole Antenna, with a home made 20-40 Wire Dipole antenna.

I want to share here my experience that should be considered just a simple personal test.

The Wire Dipole won the comparison. Signals were much more stronger compared to the ones received on the Buddipole tuned on the 20 meters band. QRM sounded higher on Buddipole.

The comparison has been conducted, in a mountain top, at 1500 meters a.s.l.,  by switching the antenna to a Yaesu FT-857D, while listining to stations calling and listening to several QSOs on 20 meters band only.

The Buddipole used is a commercia multiband antenna, self supporting thanks to the original tripod, and has a small dimensions.

The Wire dipole is easy to home made, is not multiband as the buddipole and requires a larger area to be setup. I used a fiberglass fish pole as supporting mast.

The post Buddipole vs Wire Dipole on 20m appeared first on IW5EDI Simone - Ham-Radio.

The Double Bazooka Antenna is simple to build broadband dipole antenna

Someone consider the double bazooka antenna to offer a 3dB improvement over a common dipole antenna. The only caveat is that an antenna tuner must be used.

The design is easy to replicate and uses common materials. It is mostly made of RG58U coax, #16 automotive wire, rope suspension, and any plastic that can be cut into insulators.

This antenna can been used on 80 through 10 meters by cutting it to the center frequency.

The post Double Bazooka Antenna appeared first on IW5EDI Simone - Ham-Radio.

Just found this two old antenna drawings for a four and a seven elements yagi antenna by WB7PMP.

Looks interesting plans but have not yet attempted to build them.

The post 50 MHz 4 and 7 elements Yagi Drawings appeared first on IW5EDI Simone - Ham-Radio.

PY1BEK Vertical antenna for ham radio – 40-meter ham band (7 MHz)

This self-supported vertical antenna was made with aluminum tubes of 3 m in length that have an external diameter of 32 mm and a wall thickness of 1.2 mm. The total length of the radiating system is 10.33 m and its square-shaped base measures 25 cm on a side.
To the theoretical length (1/4 lambda) was added 4% due to the width of the antenna.

The various lateral stabilizing and connecting rods of the tower are made from rectangular shaped aluminum bar (17.0 mm x 6.5 mm) and are secured to the tubes with pop-rivets that are 1/2″x 3/16″ in diameter.
Those rivets are much better than bolts and nuts – completely free of galvanic corrosion (same metal) and the pressure achieved with an hand tool will be more than sufficient to make a solid mechanical and electrical connection good for many years.

Here is a summarized list of materials: a total of nine (9) 3.0 m aluminum tubes have been used, one (1) 50mm diameter PVC tube, 2.5 m in length, 12 meters of aluminum bar (the stabilizing rods), 140 aluminum pop-rivets, and 9 inox steel braces of 45 mm in diameter.
The total weight of the radiating system is less than 15 kg, perfectly supporting winds of 90 Km/h as a lower limit in a computerized simulation and without the necessity of stays.
Since the revision date of this article, the antenna is already more than 3 years old and its efficiency is the same as when it was mounted.

The unions between the aluminum tubes was made with small pieces of copper pipe 20 cm in length and whose external diameters fit perfectly in the interiors of the aluminum tubes.
Small longitudinal “ridge” cuts (10 mm) on the tips of the aluminum tubes have allowed them to be firmly pressed, with the inox steel braces, onto the copper pipes and make good electric and mechanical contact.
The four insulators of the base of the antenna are made with Brazilian “TIGRE” PVC reducer unions.
Four (4) sections of weldable PVC (brown core), 50 mm in diameter have been used, with 60 cm of length embedded in the center of the concrete base and on the exterior tips (80 mm) two reducer unions have been joined with “TIGRE” PVC glue.
In the center are positioned 32/40 mm reducers that are then coupled via 40/50mm reducers to the 50 mm diameter PVC.
Glue is also applied on the tip of the pipe displayed above of the concrete mass.
In these insulators the four feet of the antenna are placed.
They are introduced 30 mm inside of the lesser sleeve, until they’re jammed inside.
Completing the setting, four screws of 3/16″ x 2″ cross the interior of each insulator, thus securing the antenna to the support.
The tower properly set has an upper part formed by a 6 m mast with a single tube sliding portion of 5m by which Standing Wave Ratio (SWR) adjustments can be made. After the adjustment, single inox steel brace will keep the upper mast in position.

The support insulator was buried to the soil with concrete (cement, rock dust, and 20mm stone aggregate at ratio of 1:4:4) in a squared hole of 40 cm width and 80 cm deep. In the deep end of the hole four linked 2.4 m copperweld poles had been inserted and interconnected with 25 mm2 flexible cable so they will be part of the grounding.
Measurements made with a milli-ohmmeter resulted in a 3.6 ohm when all the poles were in place.
Beyond the copperweld poles, a system of 13 radial of 10 m length, using sections of flexible copper wire (1.5 mm in 2 sections) were attached to the ground terminal.
These wires are embedded and hidden to a depth of 10 cm underground and complete the grounding.
The fact that, as embedded, the radials lose their resonance means that their exact length is not very significant.
However, their combined effect on impedance is not negligible. In practice, the ground impedance obtained was around 20 ohms.
This was then added to the theoretical impedance (35 ohms) of the 1/4 wave antenna which then became close to the 50 ohms necessary for correct adaptation to the coax cable RG-213. With the low Q of the antenna, the SWR over the whole band was well below 1.2:1.

In the top, an element was placed as a driver for the 50 MHz band, transforming the upper part of the antenna to a 1/2 wave radiator for 6 meters (3 DB of gain over isotropic). The J-Pole was made with copper pipe of 15 mm diameter and whose length was 1.47 m. It has an independent coax cable of RG-213 that goes down into the interior of one of the tubes of the antenna. This element for 50 MHz does not interfere with the main antenna that continues to resonate at 7 MHz. The SWR at 50.500 MHz is 1.0:1 and reaches 1.2:1 between 50.000 and 51.000 MHz.
My next experiment will be in making a radiating system with a J-Pole for 10 meters whose photos will be published upon its successful completion.

More information on vertical antennas can be found at this excellent site of L. B. Cebik, W4RNL.

Also, I would sincerely thanks the impressive cooperation of Ken Beck, WI7B helping us with this English translation.

73, Sergio Valente, PY1BEK

http://svcglobal.com/antena/index.html

The post Vertical antenna for ham radio 40 meter band appeared first on IW5EDI Simone - Ham-Radio.

While evaluating HF multiband vertical antenna I found this interesting review about the CHA250B by Comet.

I saved for further reference, author is K3DAV whose site is gone qrt.

Comet CHA250B HF Vertical 

By David – K3DAV  (2/7/2012)

There are a few compromise HF vertical antennas within the same class as the Comet CHA250B on the market.   

     “BUTTERNUT” makes the HF6VX, but you need to buy extra kits to add some of the bands. That
doesn’t make much sense.

     “DIAMOND” has one similar to the Comet called the BB7V. It has a cheap design with a separate
add-on load coil with a flimsy wire that connects the coil to the main element. That doesn’t
make much sense either.

     “GAP ANTENNA” makes the TITAN-DX. But in reality, it is a center fed vertical dipole. Only the
top half is a main radiator. And this thing has way too many ugly radials sticking out in all
directions that can break off in the wind.  This thing is an eye-sore.

     “HUSTLER” has the 6-BTV. Not a bad antenna, but it is loaded with several power robbing
band traps.  Again this makes no sense.

     “HY-GAIN” has the AV-18AVQII, but again with all of those power thieving traps for certain
bands, and a separate add-on load coil for 80 meters. What’s up with that?

     “JETSTREAM” makes a real look-a-like, copycat version of the CHA250B called the JTV680. But
the JTV680 is made of thinner lower grade aluminum that will break easier in the wind, and
the coil is basically a fat 50 ohm resistor type that sucks power away.

And every one of those antennas have high SWR throughout the HF band that requires you to have or purchase an antenna tuner.  That means they all have a poor impeadence match which robs even MORE of your power. (Except the JTV680 which just uses a big fat resistor to rob your power.)

Then there is my favorite.

The little antenna that could.

Just to reassure you, I do not work for NCG Company, (the parent company of Comet antennas), and they do not pay me for this review. I am just so impressed by the performance of the CHA250B, that I thought it was worth a page on my website. So take every word I say here as pure and quite honest. And I never exaggerate.

The Comet CHA250B HF Vertical.

I fondly call it my 24 foot dummy load.  The design of this antenna is so simple it is almost stupid. At first glance, it is pleasing to the eye. Nice shiney aluminum standing tall, and that’s it. No big ugly radials anywhere from head to toe. More importantly, there are NO FREQUENCY TRAP COILS to suck away your power.  The entire length is one continuous piece of aluminum tubing, and the whole element radiates RF at all times.  Actually, it kinda looks like an old style CB antenna. My first thought was, how can this thing work? It’s just a balun with aluminum tubing far too short for frequencies below 15 meters. But after my experiences using this antenna, I can tell you, IT WORKS pretty damn good. At least much better than I ever expected it would.

A diagram of the matching transformer built-into the big round black housing within the mounting bracket.

Before you decide to purchase one, keep in mind that this antenna is a compromise antenna. It will not give you top performance like a monster yagi or a perfectly cut dipole up high. But if you are space restricted like me, and want a good HF vertical to get you talking on HF, this is the one antenna to own. As I have told many hams who laugh at this antenna, “You may not give the guy in Australia a big 20 or 30dB signal, but I gave them an S-9 signal, and we had a very nice QSO.” And isn’t that the whole point of ham radio? Making the contact, and possibly a new friend? Also keep in mind that you can NEVER use a linear on this antenna. It can handle a maximum of 250 watts SSB, but only 125 watts on AM & FM. This antenna is for the space restricted ham who only uses the 100 watts of power out the back of the radio.

These are quotes from the NCG website about their own product….

• “If you have the space, budget and desire to erect a full size antenna system we suggest you do so… bigger IS better. However…if you live in an antenna restricted area and must manage with antenna or space restrictions, or you simply wish to operate incognito,  you will be forced to make significant antenna compromises.  The CHA-250B will make the most of these circumstances!”
• “The Comet CHA-250B is a newly design broadband vertical with NO GROUND RADIALS. This antenna is EXTREMELY easy to assemble, requires no tuning or adjustments and VSWR is under 1.6:1 from 3.5MHz – 57MHz!”

And for you guys who already have yagis or dipoles on huge towers, the CHA250B is a good standby, or can be used as just a good omnidirectional monitoring antenna to see what’s on the bands. This antenna is quiet with great ears. And it covers the entire HF spectrum, so it makes a fantastic general coverage antenna. It also covers TX on the MARS/CAP frequencies.

The CHA250B comes in 5 pieces. Assembly took me 20 minutes. The entire antenna is 6068 aircraft aluminum, and fits together easily.  Each section going up fits inside the one below it. Two of the sections are pre measured with pre tapped holes for inserting a small sheet metal screw. The other two sections must be measured to set them correctly. They too slide inside the lower section, but are held in place with a hose clamp. You only need to measure the element a few inches from the bottom end that slides into the other section. The instructions give you the exact measurements to use. Mark the measurement with a marker or a scratch, then insert the element exactly to the mark, then tighten the clamp. Then you are ready to raise the antenna into it’s new home. From opening the box to complete installation took about an hour.

The specifications for the CHA250B are very simple. Here is how the NCG website list them.

Broadband: TX 3.5 – 57MHz RX 2.0 – 90MHz
VSWR: 1.6:1 or less
Max Power: 250W SSB, 125W AM-FM
Impedance: 50 Ohm
Length: 23’5″
Weight: 7 lbs 1 oz
Connector: SO-239
Mast Size Required: 1″-2″ diameter
Max Wind Speed: 67MPH

The following is the measured wavelengths on particular bands for the CHA250B. No tuner is needed except for 160M as this antenna is not designed for use on 160 meters.

At 1.900MHz this antenna equals a 0.045 wave. (Ant. Tuner Required)
At 3.600MHz = 0.084 wave.
At 60 meters = 0.120 1/8) wave.
At 7.100MHz = 0.166 wave.
At 10.130MHz = 0.236 (1/4) wave.
At 14.200MHz = 0.331 (1/3) wave.
At 18.170MHz = 0.424 wave.
At 21.200MHz = 0.495 (1/2) wave.
At 24.950MHz = 0.582 (5/8) wave.
At 28.500MHz = 0.665 (2/3) wave.
And finally at 50.000MHz = 1.165 wave. Too long for 6M, but still works.

NO TUNER REQUIRED FOR HF. NO KIDDING!

The entire antenna is just over 24 feet tall including the base load coil and mounting bracket. The coil is built into the bracket, and is the most important part of the antenna. The coil is built like a transformer, and provides a nice 50 ohm load on all bands. NO JOKING! I put my MFJ-269 analyzer on this antenna including the 60 feet of coax into the shack. I can spin the tune dial on the analyzer from 3.5MHz continuously scanning the entire HF spectrum through 54 MHz, and the SWR never goes above a 1.6. It is usually near flat except for a few band edges. When I checked below 3.5MHz or above 54MHz, the SWR starts to climb fast. But between those two frequencies, it is great. Even on 60 meters. I am not exaggerating. It really is that good. You do not need a tuner with this antenna on any HF band. As I said, the load coil is a transformer, but it acts sort of like a dummy load. They take a tap from the coil through capacitance to feed the main element.

There is only one exception, and that is on 160 meters. The CHA250B is not designed to cover 160M, so a tuner is necessary. See down below for more details about this antenna and 160 meters.

No counterpoise or radials required. REALLY!

But they can help.

Because of the load coil design which uses the coax or metal mounting pole as a counterpoise, you do not need ground radials or counterpoise wires with the CHA250B. It works quite well without them. I can tell you this from my experience. My first contact on this antenna was a ham in Scotland on 20 meters. I only use the 100 watts from my Icom 746PRO. We talked for about 15 minutes and he gave me a signal report of S-9 to 10dB. I had about the same on him. He never seemed to have any problems hearing what I said, as he always responded to the points or questions I made. I knew at that point that this antenna was pretty good. By the way, I only use LMR-400 coax with all of my antennas including the CHA250B.

I used to talk with a few guys in a free-for-all QSO just before sundown every night on 75 meters. 3805kc to be exact. I am in central PA near Harrisburg. The others were all around PA with one guy in upstate NY. He would get an S-5 or S-6 from my little antenna over 120 miles away. But after the sun went down, I talked up and down the eastern seaboard. A friend close by to me suggested I install a couple of counterpoise wires. So we cut 2 wires, one at a 1/4 wave on 75 meters, and the other to a 1/4 wave on 40 meters. My friend in upstate NY said my signal went up to an S-9, bordering on 10dB. So it made an improvement. This is something to note about the CHA250B. It can run without the counterpoise wires, but it helps to add them.

BUT! There’s A Bonus Feature I didn’t Count On.

160 METERS.

The CHA250B antenna is not designed to work below 80 meters. At least according to the manufacturer. But just out of curiosity, I tried it on 160 meters. Keep in mind that my CHA250B is only 20 feet from it’s mounting bracket to the ground, and I use LMR-400 coax. So as they say, “your milage may vary”. The SWR on 160M is right on a 3.0. I hit the button for the auto-tuner in my 746PRO, and in 5 seconds it tuned it to flat. So far on 160 meters, I have worked NY, NJ, IA,OH, IN, VA, and NC. Not too shaby for a 23.8 foot dummy load. I know it is nothing compared to a good 160M dipole, but it works and I made contacts.

As for performance the CHA250B actually covers the frequencies as advertised, but it has it’s limits. I have found the CHA250B to work very well on 75/80, 60, 40, and 20 meters. I have now worked all continents (Except Antartica) on those bands with it. Usually with good reports. I have even broken through pile-ups with just 100 watts. But as you go above in frequency, the performance slightly drops off, but not so bad that you can’t still make good DX contacts. I find 17 and 15 meters to be pretty good. 12 and 10 meters is fair to OK, but it could be better. But even though the manufacturer says it works on 6 meters, it is fair to poor on 6 meter performance. It is over a full wave on 6M, so I didn’t expect too much up there. My old GP-15 was 200% better on 6 meters. But it does work there.

So I have come to certain conclusions on my antennas. The CHA250B works very well for me on 160 through 20 meters. So they are the bands I use this antenna for. I have a Solarcon I-MAX 2000 for 17 through 10 meters. The I-MAX 2000 is the best vertical antenna for these bands. It performs better on 17 and 15 meters, but a whole lot better on 12 and 10 meters than the CHA250B. And I already have a Comet GP-9 for 2M/440, and a Dominator 6M for 6 meters.

I know of several hams that have purchased the other brand name verticals I mentioned at the beginning of this article, and they were not all that happy. I talked them into trying the CHA250B, and they were very surprised at how well it works for what it is. They all agreed it was an improvement over their original HF vertical purchases. All of us so far believe that it works at least better than we thought it would for a compromise antenna with such a simple design.If you have any questions about the CHA250B contact me at kedav@msn.com

The post Comet CHA250B Review appeared first on IW5EDI Simone - Ham-Radio.

If you have ever tried transmitting on HF from a tall block of apartments, where it’s just not possible to erect a substantial aerial system, then this article is for YOU!

If you have never had to try…consider yourself extremely fortunate!

The limitations imposed are not so much that of limited space (although this can be a problem) but strict Rules and Regulations that prevent the erection of any beam or vertical rod aerial.

However, the very fact that the signal is going to leap into space from a good height above ground can be, in certain respects, a bonus, so all is not lost.

It IS possible to install an aerial…a wire aerial and using low power to enjoy some interesting contacts. The satisfaction of making contacts can be most rewarding.

What we need to do is be a little sneaky here. By this, I mean that we should just fit a length of wire, discreetly, tune it up and have a go! Perhaps you have already discovered or learned from others that applying in the normal way for permission will, almost certainly, result in the request being denied.

Let us now consider a few things obvious to some but which may have never occurred to others. A thin gauge wire against a pebble-dashed or concrete building, when fairly high above ground, will go virtually un-noticed, providing it is fixed into position quietly, during darkness and does NOT cause any flickering of neighbours’ television screens while they are watching Coronation Street!

The key factor in NOT giving any interference is in using an ATU (Antenna Tuning Unit) AND a Low Pass Filter which should allow low HF (High Frequency) signals to pass through, as we want these to radiate, but should suppress any VHF or UHF (Very High Frequency and Ultra High Frequency) signals or harmonics from the lower frequencies which could cause interference to television reception. One of the Golden Rules in determining this is that should you be giving yourself any flickering on any television channel then you can be fairly certain that a neighbour is also getting it and that is not acceptable!

Keep it simple!

A true Long-wire would be several full wave-lengths at the operating frequency. Such an arrangement is impractical for our requirements and in any case would fire straight off the end heading into space or down to the ground! What we are seeking is to send out a lobe that covers an area of the planet likely to include other radio amateurs.

Ideally, we should use a length of wire that is at least a quarter wave-length long, but preferably longer, at the lowest frequency we wish to operate on. This would mean a wire at least 130 feet long for Top Band or 1.8 MHz, but in practice I suggest that you aim for a length of 90 feet or as much as you can reasonably get away with.

As shown in the diagrams, #12 or #14 gauge wire is suitable because it will be strong enough yet hardly be visible. Stranded wire is preferable to hard drawn (solid) copper wire as it is more flexible and resistant to fracture from movement in the wind.

The Vertical will radiate the best pattern, so this would be my first choice.
If you have access to the roof, with the help of your wife or friend, lower a length of twine or strong nylon fishing line down to the point where someone is able to grab hold of it and pull slack into the room or balcony. Now join this line to an end of your wire. If using nylon line which is slippery, tie a knot using several turns and tape around the end to stop it from slipping and becoming free!

Once the end of your wire has been pulled up and your assistant has grabbed hold of it, go up to the roof and get the end fixed into position as soon as you can. This may involve some leaning over, so don’t attempt this if you are nervous of heights and if you do attempt this TAKE GREAT CARE!

You need a strong support point which in turn will invariably require the screwing in to the masonry of a hook, screw or masonry nail. Any of these is going to require either a short burst with a masonry drill (battery operated portable drill) or several taps from a hammer. I would prefer the drill myself. (If it were me doing this, I would be inclined to do this fixing one night and then wait several nights before pulling up the wire and attaching it to this fixing). I would feel inclined to attach a wrist strap to any drill, hammer or tools used for this task rather than risk an item slipping from my grip and dropping. TAKE THE GREATEST CARE!

The observant among you will have noticed that in the diagram, I suggest the use of “Blue Tack” to keep the wire away from the actual structure and stop it flapping about. This should only be a temporary step until you are satisfied that this can work for you. The best method of support is to use TV stand-off insulators at the far end (top) of the wire and two or three along the length. I appreciate that this might not be possible unless you are friendly with the dwellers in apartments between yours and the roof. Before fitting anything permanent though, I would want to make sure my aerial is going to work, so a cable-tie from wire end (small loop) to the fixing screw/eye will be fine for tests.

If there is a drainpipe running down the building and close to your apartment, you might want to consider passing your wire through a length of thin plastic pipe and secure this to the drainpipe where, if it is the same colour, it will look like part of it. Keep an eye out though for maintenance workers and if you see one showing more than a passing interest in your pipe, offer him a cup of tea and biscuits and explain your dilemma…he’ll probably wink at you and say no more!

There are no hard and fast rules regarding working out length except as said earlier, this wire should be longer than a quarter wave-length at the lowest operating frequency. Use this formula to work out how long your wire needs to be at the lowest quarter wave frequency:

L (length) = 234/F (frequency in MHz)

/ = Divide

As an example, suppose you wish to operate the wire at 14,250 KHz (14.25 MHz).

Length = 234 / 14.25 = 16.42 or 16feet 3 and a half inches. (Approx)

Because your wire will be end-fed, it is going to have high impedance so you will need a tuner and SWR meter between the end of the wire and your transceiver.

See the diagram for details of how to make a simple tuning device that should tune up any random length of end fed wire. Using low power, say 5 watts or less, then any tuning condenser which has vanes, removed from an AM Wireless, will do the trick. Just remember that the wider the gap between vanes, the higher the power it will handle.

For the variable inductance, if you can find a “roller-coaster” at a Radio Rally, that would be ideal. Failing that, make a former about 2 inches diameter (kitchen roll core?) and around 6 or 7 inches long (why doesn’t this guy use metric?) and use #14 gauge or thicker.

Wrap your wire around the former with a gap of a sixteenth or eighth of an inch between turns. When using the finished coil, a short lead with crocodile clip (as shown in diagram) can be used to change contact from one part of the coil (inductor) to another. Experiment with different combinations of coil coupling and tuning capacitor settings. Make a written note of which settings give best match for given frequencies.

NEVER MAKE ADJUSTMENTS OR COME INTO CONTACT WITH THESE PARTS WHILE TRANSMITTING RF!

I knew a Radio Amateur who lived in a tall block of flats not far from where I live. He tried many frequencies but found he could achieve excellent results from the 40 Metre band. This was the band he used until he became Silent Key. He found he could have regular contact with UK stations and European neighbours during the day time. In the evenings and particularly in the early morning (0100+) he could work DX and had confirmed contacts from as far away as Tierra Del Fuega which is down by Cape Horn at the tip of South America. Eric accepted his lot and was happy to be able to work anything at all. His aerial was a wire around his living room skirting board under the carpet! He used CW and less than a couple of Watts for all his contacts!

Inverted Vertical

Choosing which of these two aerial methods to use will depend on how high in the apartment block you live. You could try both of them. The simplicity of this second way is that you can easily lower your wire, with a small canvas bag of sand as a weight at the bottom. This will keep your wire straight while you are lowering it and also keep the wire from swinging too and fro once it’s in the final position. You could also use a section of broom handle or similar with a V notch cut in one end to keep your wire away from the building structure. If you feel particularly paranoid, you can lower this when it gets dark, use it, then bring it back up before going to bed.

There is not much else for me to tell you, but I always get a feeling I may have forgotten something!

Ah, just remembered…should you fail to achieve a low SWR (standing wave reflection) no matter what you do, you may wish to consider using a counterpoise. This is, in effect, the second part of a half wave dipole so if you want to give it a try, cut a length of wire equal to the length of your main aerial. Connect it to the Earth/Ground side of your tuner and spread the wire along the corridor and under carpets in your apartment. This can be insulated and can improve your signal considerably. What it does is provide the simulated ground which is missing because you are living so far above it!

As with my previous article, readers must be prepared to solve their own problems. There are plenty of books in the Library or at your local Radio Club that will give additional information on these and other designs. I do NOT pretend to be an “authority” on the subject, so please just accept these humble offerings as an incentive for you to try things out for yourself.

You must also take responsibility for your own actions as neither myself, the Website Author should be deemed responsible for any use or misuse of this information or for being the cause of any adverse circumstance!

Si fallatis officium, quaestor infitias eat se quicquam scire de factis vestries
(If you fail, the secretary will disavow all knowledge of your activities)

This article, by Mel Fisher G4WYW, was found on http://www.southgatearc.org/articles/g4wyw/apartment/apartment.htm

The post HF antennas for high rise dwellers appeared first on IW5EDI Simone - Ham-Radio.

First, please excuse my artistic abilities. The diagrams are basic but show the rudiments of this excellent aerial, which is ideal for the newcomer to HF and those on a small budget as well as those with little space to erect large arrays!

Please note that my calculations are worked out using feet and inches because that’s what I grew up with! The reader who understands the Metric System should have no difficulty in converting to Centimetres and Millimetres but this article will use Feet and Inches.

Before outlining the construction, I would just add that when I was first licensed, I tried various aerials, verticals; inverted V’s, inverted L’s and wire dipoles. I finally gave this design a go. It was a brilliant success and I had a confirmed (QSL Card) contact with CE0ERY Hector on Easter Island on 30/04/1984 quickly followed by VK’s, ZL’s, and a string of exotic DX throughout the Indian and Pacific oceans.

YES using this same design I am about to explain to you in the following paragraphs!

WHAT YOU WILL NEED

You will need some wire…I have always found that old or new house wiring cable is an excellent source of wire but will need to be stripped from the grey outer insulation. The red and black pair of wires needs to be further stripped from their coverings. If you don’t fancy this task, it will still work, BUT it’s better to use naked copper wire for best results.

Here’s how I strip wire in long lengths.

First I use side cutters and cut into the wire from the end, trying to keep close to the bare earth wire that is in the centre of the cable and which runs along the length.

Once I can get a grip on the end of this earth wire with a pair of long nose pliers, I twist a few turns around the nose of the pliers and gently pull. Soon there will be enough slack grey outer sleeve to allow it to be held in place with the feet standing on it firmly. I have also tied the end of the grey insulation (with red and black wires) to a door handle or vice handle.

Once the thin earth wire starts to strip it usually comes easily as long as a steady firm pressure is applied and sudden jerks are avoided. When the thin wire has been removed from the entire length, having acted like a cheese cutting wire, the red and black should peel out without any bother.

The 75 ohm twin feeder that I used was cadged from a BT worker that I spotted while driving home. I approached him and told him what I needed some for and asked if he might be able to oblige. I made sure that he spotted the couple of old One Pound notes that I held in my hand. He cut me off a generous length but refused to take my money. I told him I owed him, thanked him and rushed home to start making my aerial.

You will also need a small square or oblong rectangle of insulating material such as Perspex or Paxolin. I didn’t have any so I made do with some plywood which I drilled and varnished until I was able to obtain some better material later. It is also possible to use a custom centre piece complete with female coax socket for the feeder and two wing nuts (butterfly nuts) at each end of the T-piece where all the bare ends can be twisted together and connected. This is the quickest method and gives reliable results but regular swinging in any wind WILL eventually cause breakages at the connections! A proper centre piece with female SU socket is not too expensive but you’ll experience greater satisfaction if you make up the part yourself.

To avoid becoming confused, it is preferable to work with one pair of quarter wavelength wires at a time and to use a short strip of masking tape folded and pressed together over the end of a length of wire and marked in Biro 10 M and 15M and 20M as appropriate.

After you have ended up with pairs of wires, all cut to length ready for connecting to your centre piece, the next thing to do is to connect all the ends together and to the feeder.. Look at the enlarged diagram showing the centre-piece to understand how this is done. Basically, the end of each wire is passed through two holes, an overhand knot (one turn over the wire and through the loop) pulled tight will prevent the wire from being pulled out of the centre piece. Strip off about half an inch of insulation from each wire end after the knot has been tied and connect all the ends on one side of the connector centre piece and to this should be added one side of the 75 ohm Twin Feeder which is commonly used as telephone wire leading from telegraph poles to the house and which is a superb match when used as a feeder or Transmission Line for this aerial design.

After fitting, joining and soldering the joints, each bare wire and soldered joint should be covered by a blob of bathroom sealant or other rubberised substance which, when dry, should offer some protection from weathering. It will pay dividends to check and perhaps redo this each year with your annual inspection and maintenance. What do you mean, you don’t do annual maintenance?!

Although the final choice is completely up to yourself as to which band you have at top, bottom or in the middle, the results I achieved came from having the shorter 10M pair at the top, the 15M pair in the middle horizontal position and the 20M pair at the bottom working as an inverted ‘V’. The reason why this design gives such good results is because of this: At ten metres the 10M section acts as a half wave dipole but at the same time the 15M section also radiates some lobes and the 20M section acts as a full wave dipole on 10 metres in addition to the radiation from the actual 10M section.

Now that you understand how each section interacts with and reinforces each other section, it is time to look at how the individual lengths are worked out.

L (length) = 468/F (frequency in MHz)

/ = Divide

As an example, suppose you wish to operate the 20M dipole at 14,250 KHz (14.25 MHz).

Length (overall of half-wave) = 468 / 14.25 = 32.84 or 32feet 8 and a half inches.

(You will see that I have approximated the inches. Such a small inaccuracy will not make any noticeable difference!)

Divide 32.84 by 2 to give 16.42 feet, the length of each quarter wave section that makes up the half-wave dipole length.

Purists may wish to add an inch and a half to allow for the knots at the support points at each end. Where the bare end of a wire connects to an insulator such as an egg type insulator, pass the wire through and around the insulator then twist the end back over the main wire with a series of small twists or turns. (Bare wire!) The length in this case will be to the centre of the bend where the wire curves back on itself at the insulator and NOT to include ALL the total length of wire providing it does indeed connect back on itself and in effect is shorting itself out!

So there you have it. The formulae to work out your own individual measurements and the instructions for putting it all together.

PLEASE REMEMBER NEVER TO ALLOW ANY OF THE SECTIONS TO BE CUT AS A HALF WAVELENGTH FOR A BAND FOR WHICH ANOTHER SECTION IS THREE HALFWAVES!

For example, if you cut the lowest dipole for 40M, you would not wish to cut another section for 15M as they would interact giving a wrong feed-point impedance in addition to a skewed radiation pattern.

In practice there will be small differences in impedance and standing wave ratio (SWR) in each different location. This is due to conductivity of soil, height above ground, wire type and other tiny factors which we have all experienced in our hobby as Radio Amateurs from time to time.

In conclusion, I do not claim this as my design. Indeed, it can be found in varying forms in a number of books on Antenna Design. I have just presented it in a way that I hope may be attractive enough to cause you to give a try to making one. I have tried to explain in such a way that you can picture the finished aerial in your mind.

If you are unwilling to construct an aerial that resembles a Union Jack flag in wire, you CAN build it so that all sections lay alongside of each other BUT ONLY if the insulation is retained on each wire component. It won’t work quite as well as the described aerial but it will work.

I have used 75 Ohm Co-axial Cable in place of the twin feeder and it still worked surprisingly well. Once you are satisfied that it exhibits low SWR (standing wave reflection) at each frequency it is cut for, you can just get on and use it without the need for an ATU (antenna tuning unit) except for at the band ends. I am of the opinion that far too much fuss is made about SWR measurements that hardly deflect a needle of a meter. You can fire up into an SWR of 3.0 and there will be hardly any difference in the received signal at the other end of the contact!

Your Transceiver will soon let you know if things are not quite right!

I might have been extremely lucky, but I just made mine, stuck it up, ran the twin feeder to my transceiver (Yaesu FT 401-DX) and started using it straight away with good effect.
I DID have a good earth rod though, driven into the ground to a depth of six foot (6′) which I would advise you to have no matter which type of HF wire aerial you use. On the night that I worked Easter Island, I called many times without getting a reply. So I went and sprinkled a packet of salt over the top of my earth rod and splashed more than ten washing up bowls of cold tap water over the area. When I returned to my station and called again, I was answered immediately and Hector said how pleased he was to hear and work a ‘G’ station. We exchanged reports of 5/5.

The reader is expected to resolve his/her own problems and the writer does not accept any responsibility for wrongful use of the information provided. All information is supplied in good faith.

Get cracking now… and good luck with your CQ calls!

This article by Mel Fisher G4WYW, was found on http://www.southgatearc.org/articles/g4wyw/tri_band/tri_bander.htm

The post An effective 3 Band Wire DX Antenna appeared first on IW5EDI Simone - Ham-Radio.

Article by W2BRI

After many requests by Ben W4KSY*, someone I consider to be my loop mentor, I decided to post a page about my 80 meter magnetic loop. The idea for this loop began with my purchase of a new vertical antenna. Now when you think of 26 feet of antenna, it doesn’t seem that large until you put it together. Now add a couple of 1/4 wavelength 80 meter radials, and the vertical antenna solution starts to get big. Now, I’m into efficiency, and I wanted to string four radials five feet above ground at 90 degrees, and set the whole system up in the best possible way. However, when I moved into my new house, I had the disturbing reality that I had many power lines running across my property and I also didn’t have close to the room for 1/4 wavelength or even 1/8 wavelength radials (even for 40 meters). So I figured I’d never get on the low bands and I’d have to live with 20 meters forever. Don’t get me wrong, I love 20 Meters.

It’s no secret, I am a big fan of Force-12 antennas. I own a Force-12 C3SS triband beam, and can’t complain a bit about it. I call CQ on that antenna, and I get five people coming back to me almost every time. While I was at the ARRL conference last year I met Tom, N6BT one of the owners of Force-12, and picked up his book “Array of Light.” The book chronicles his experiences designing, building, and putting up thousands of antennas (yes, thousands!). It is a great book in my opinion, and a must read for those interested in understanding the ‘reality’ of antennas. As I went through the book I found a chapter on magnetic loop antennas and their high efficiency. The wheels in my head started turning, and I thought, I could manage putting up an 80 meter loop in my backyard. Maybe 80 meters isn’t out of my grasp.

So I picked up the phone and called Tom at Force-12 and asked him what he thought. He told me sure, he’d be happy to build a loop for me but the capacitor arrangement and the loop support would be my problem. I agreed and after several emails back and forth and a couple of months (and dollars), I received a very large box on the door steps of my house. The box was filled with 2 inch 4 foot lengths of aluminum. Each piece was tapered at the end so it would fit into another piece with about 3 inches of overlap. Then a bolt was inserted between the connected pieces, and each section was completed. the corners had a similar tapering, and it took a whole 15 minutes to put it together by the garage.

At first I used coaxial stubs for a capacitor. Tom suggested this strategy. You can cut coax and use it as a capacitor — take several different lengths of coaxial stubs equaling different amounts of capacitance, and move from band to band. I even loaded the loop onto 160 meters, but that’s another story for later. I built two wooden supports for the loop with my friend Steve, and we attached the loop into place. I was ready for 80 meter action.

Great, I had the loop built, but getting it to match and work was a whole different story. I had read many articles by Ben W4KSY about loops, so I thought since I was having some problems I’d ask him via email what to do. Well he was kind enough to instruct me about how the feed system works (the one from Tom was too small), and how to re-work it and what to expect. We emailed a bunch of times and I finally got it where I wanted it, 3.863 at 1.1 VSWR with about 10 KHZ in either side of bandwith (remember, with loops you don’t want a whole lot of bandwith — but this was an acceptable range).

With excitment that first night I turned on the rig to 3.863, and heard a bunch of guys in the bay area (from my QTH in Los Angeles). I popped my call in with 100 watts, and they came back first time around. I heard everyone in the round table, and everyone heard me. Night after night, QSO after QSO, 99% of the time, everyone hears me and I hear them. No problem. And this was during summer conditions. I worked many stations regularly from Oregon to mobiles in Wyoming, stations in Arizona, and others up and down the coast. Now when the propagation changes in early fall I am working stations farther out, Texas, Colorado, and Oklahoma. I am looking forward to winter conditions to give more reports.

I eventually upgraded the capacitor to a Jennings vacuum variable 5-750 pf with a over 12KV rating (cost around 200 bucks), and fixed on a motor to drive the capacitor up and down the bands. The motor controller is in the shack and I use a pair of DPDT relays connected to momentary pushbuttons to pulse the motor onto frequency. It works like a champ.

So, can you work 80 meters with a 12×12 loop 6 inches off the ground, yes! And you’ll have a blast doing it.

For more technical explanations I plan on adding more info relating to large loops on the site, and will be happy to email.

73,

Brian, W2BRI

this article was previously available at  http://www.standpipe.com/w2bri/80meter.htm

The post Magnetic Loops by W2BRI appeared first on IW5EDI Simone - Ham-Radio.

Co-Phasing

Co-phasing or “stacking” has long been a way to get high gain from antennas. Co-phasing involves placing two (or more!) identical antennas either side-by-side or one over top another (“stacking”) at a certain distance apart (usually a 1/2 Wavelength or more) and feeding the antennas in-phase. The result is 3 db more than just a single antenna. In my opinion, this is the absolute way to go with beam antennas instead of going with say, 8 elements beams, it would be much better to go with co-phasing two 4 element beams. If you look at the gain figures for a 8 element beam, you see that you will end up with more gain if you co-phasing 4 elements instead. If you are considering co-phasing antennas for your mobile, better check out the “Mobile” section first.

Before I get into the details of co-phasing, lets consider what antennas we should considered co-phasing. The reason I say this is because co-phasing would not make sense on certain antennas, when you could just use another type of antenna (with more gain) that would be simpler. For instance, you could take two A99’s (1/2 Wave verticals) and co-phase them, but, why? It would be more simple to get a 2 element yagi, and mount it vertically. It would have more gain than two co-phased A99s (and I hope you are not taking their advertised gain figure of 9.9db and adding 3db onto it, if you think co-phasing two A99s gives you 12.9 db (more than a 4 element beam!) you better go back and read how much gain your A99 really has in the “Verticals” section).

Lets look at the pattern of a single 1/2 wave vertical and the effect that co-phasing has (by showing the pattern of two co-phased 1/2 wave verticals). As you can see in figure 1 the pattern is now focused mainly into two directions. If you want to have a pattern that is focused into two directions only and do not want the single direction only that the 2 element yagi gives you, you could make a yagi that does not have a reflector element, but two director elements. This would have more gain than two co-phased A99s and take up a lot less space. Figure 2 show a possible arrangement for phasing two 1/2 Wave vertical antennas.

Figure 1 – Comparing the patterns of a single 1/2 Wave vertical and co-phased 1/2 Wave verticals. This is the result of co-phasing any two omnidirectional antennas.

Figure 2 – How you would mount two 1/2 Wave verticals (or 5/8 Wave verticals) if you wanted to co phased them. Maximum signal strength is straight into and out of the figure (towards you, and straight in front of you).

The only antennas I could really recommend co-phasing are beams with 3 or more elements. The work involved is serious, and with other antennas, there are simpler solutions to stacking.

Why co-phase antennas then? Well, co-phasing beams with 3 or more elements results in seriously high-gain. If you are serious about phasing your antennas (any antennas, do not let my ideas and opinions stop you from co-phasing your antennas) then lets get started.

Getting Down to Business

First off, stacking takes a lot of planning, time and money. More planning than anything. Starting off with the distance you should use, let me discuss what good stacking distances are. Most text books say that the spacing between co-phased antennas should be at least 1 wavelength (36 feet!). But in practice at 27MHz, we see that stacking at 36 feet is tough. The rules go like this, for higher gain antennas larger stacking distances are needed to realize the full 3 db gain increase. This means for your 4 element beam, to get the whole 3 db increase you should get them as far apart as practical. I have instructions from Antennas Specialists (the maker of the Moonraker 4) on how to stack 2 Moonraker 4’s. The distance they recommend is at least 24 feet. If it were me, folks, If I were going to attempt this, I would get it out to at least 27 feet. There is no sense in putting up huge antennas and keeping them so close. For lower gain antennas (the A99 (1/2 vertical) for example) it would be perfectly acceptable to stack at 1/2 wavelength apart (18 feet). I would not recommend co-phasing any CB antennas under 1/2 wavelength though (except for mobile antennas where you can only go so wide). What happens is the radiation patterns overlap so much, see figure 3, that there is no effect from co-phasing. The pattern combines and ends up the same shape as a pattern from the single antenna. It is necessary to separate the two patterns far enough that overlap is not great, and then you will get the effect of the pattern reforming and creating a much narrow front lobe as shown in figure 4. Its as simple as that.

Figure 3 – On the left is the radiation pattern of co-phased beams that are too close to each other (say 9 ft apart). The pattern on the right show the pattern of single beam. When stacking distances are too close, there is not really any effect from stacking, the pattern remains the same as having a single antenna.

Figure 4 – The result of stacking beams with a wide enough spacing. You can see that the near field patterns of the single antennas just touch (this requires wide spacing, say 36 feet or more), the resulting pattern is re-shaped and has the full 3db increase.

Lets look at some possible physical arrangements for co-phasing. Figure 5 shows two cubical quads stacked side-by-side. This is the most common arrangement. A stacking boom must be made to support the two antennas. HERE is the plan for a stacking boom designed by Antenna Specialists. I do not know of anybody that commercially makes a stacking boom. Another possible combination of stacking two antennas is shown in figure 6. This is okay if you only need really high gain in one direction, because if you require that this arrangement be able to be rotated, the WHOLE tower will have to turn! It has been done, but the construction problems are formidable. You can even stack more than 2 antennas at a time. Any even combination of antennas can be co-phased. Figure 7 shows an example.

Figure 5 – Possible physical arrange for co-phased cubical quads. They really aren’t stacked (one on top of the other like figure 6) but most people still call these “stacked” beams.

Figure 6 – Another way to mount beams if you want to co-phase them. This is a set of 4 element Yagi’s mounted over one another. As you can see, the whole tower would need to be rotated in this arrangement. You can buy commercially available tower components to solve this more easily than rotating the whole tower, but it is expensive! I recommend mounting them side-by-side like figure 5

Figure 7 – You do not have to stick to just co-phasing two antennas. Any even combination of antennas can be co-phased. The gain of this setup is monsterous! If this were 4 element quads you would have 12db + 3db + 3db = 18db. You only get 3db for adding another set of antennas. Would this every be a great setup. If you every do this, you better tell me so I can come see it while its still up! I had pictures of stacked Moonraker 6 antennas that I need to scan in. The antennas only survived a week on a West Virginia mountain. The stacking boom was made from a piece of 40 Foot Tower!!!

I will leave the construction planning of supporting such huge antenna setups to you! I would suggest using aluminum for the stacking boom and use guy cables (3 of them) on the stacking boom made of phillystran. Phillystran is a insulating material that will not stretch and is invisible to RF. Hey, if you are going for it, do it right! Minimize the effect your supporting structure has on your antennas patterns. Steel guy cables cause undesirable pattern interference. HERE is another document from Antenna Specialists on how to orient your Moonraker 4 antennas on the stacking boom. HERE is one last document of a crazy guy climbing a skinny tower to put rather large stacked Moonraker 4’s up.

The All-Important Step

Now that we have down the distance we should use and the arrangements we can use to stack antennas, most importantly we must get the feedline right! You must feed your antennas properly. It is not called co-phasing for nothing. If you use random amounts of coax, your beam will be fed out-of-phase with one another..let’s just say this is not what you want!

Figure 8 shows the all important arrangement of coax you must use to feed your phased antennas right. A odd multiple of 1/4 Wavelength 75 Ohm coax must be used. Check out the “Coax Basics” section for information on cutting coax to certain lengths.

Figure 8 – The most important step in getting your co-phased antennas to work right. 75 Ohm coax is used as an impedance transformer to match placing two 50 Ohm loads in parallel back to 50 Ohms. Note this is only for co-phasing two 50 Ohm antennas. I am not going to cover harnesses for more than two antennas, if you are going to co-phase more than 2 antennas at a time, you better be reading more than just my web page for co-phasing! Also….each side of the harness must be the same length

I will go over some common coax types here to help you out. Please, please, do not “assume” that you can just cut your coax close enough and you can just adjust the antennas. This step will make or break your setup. You must verify your coax type, get the right velocity factor and cut it right. Again pick a frequency in the middle of where you talk…or pick the exactly frequency you use most.

Here are some examples (for common 75 Ohm coax):

More example. Say we have built our stacking boom for our Moonraker 4’s 27 feet long (our Moonrakers will be 27 feet apart boom to boom) and we got RG-59 Foam Coax to use for the co-phase harness. We must make each leg to the antenna (from the Tee connector) 21′ 3 1/4″. As you can see, if we stretch that out straight across we are going to have a ton of excess coax, we only need 13 1/2 foot for each leg, but we have to use 21′ 3 1/4″ on each side to match them up right and feed them in phase. Take the excess and spiral it down the stacking boom. Do not do it in a tight coil, but make a long wide-spaced spiral around the stacking boom towards each antenna starting after the Tee connector.

Tuning the antennas

Before you place your antennas up on the stacking boom with the co-phase harness you should adjust each one individually. I would place it up on the stacking boom where it will be, then hook the coax straight from the radio to it (preferably use 1/2 multiples of 50 Ohm coax from the radio to the tee connector, or antenna in this case) then tune the antenna for whatever ever frequency you are centering your design on. Remember, your antennas have to be adjusted for the exact same frequency and the co-phase harness must be cut for that frequency also. So after you get both antennas adjusted to have the exact same SWR curves as one another, you are ready to connect up your co-phase harness. Be sure that you have oriented both antennas in the same manner. For instance if the gamma match is pointing right on the right antenna, be sure that it is ALSO pointing RIGHT on the left antenna. If you have followed these directions, your array should be close to where you tuned the individual antennas for. It will not come out exactly where you tuned the individual antennas for because the odd 1/4 wavelength multiple of coax is going to induce confusion to your SWR meter again (only 1/2 wave multiples give accurate readings)… but remember the actually SWR at the antennas feedpoints in theory will be were you set them for. If SWR is way out of whack, you may have to go back and readjust your antennas again. Or, try rewinding your co-phase harnesses again in a different way. Instead of making wide space wraps around the stacking boom, run the coax straight down to the antenna from the tee, and wrap a tight coil around the stacking boom right where it connects onto the antenna. The wraps of coax should be touching each other. This acts as a RF choke (prevents RF from flowing on the outside of the coax) and prevents feed line from interacting with the antenna pattern. This may be the cause of your problems. If you antenna uses a gamma match or balun you should not have this problem though. But, may the force be with you!

Article by Scott scott2RP789 originally available at http://signalengineering.com/ultimate/co_phasing.html

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Angle of Radiation

Most of us think that our antenna’s “shoot” the signal straight off the end (if its a beam), at right angles from the antenna. I have even seen some operators (mainly ones who live in valleys) bend their mast so that their antenna does not sit with the boom parallel to the ground (don’t do it, read on). They hope to shoot the signal up out of the valley. Well, this is not how things work. The angle that the signal comes off the antenna, is mainly controlled by how high the antenna is from the ground. This angle that the signal takes off the antenna is sometimes called the “Angle of Radiation” or “Take-Off Angle”. You can see what I mean by take off angle by looking at figure 1. Most of you probably thought the signal came off at a 0 (Zero) degree angle, right? You would have to have your antenna over 500 feet in the air for this to happen!

Figure 1 – The angle of radiation. This figure shows a vertical antenna, but the concept is the same for all types of antennas. The shaded area shows the most useful angles (10 – 20 degrees). To get this angle of radiation you will need to have your antenna from about 70 ft – 25 ft, respectively.

Quite simply, the higher then antenna is, the lower the angle of radiation. Why is this angle of radiation important? Simple. Lower angles of radiation are better for two things. One, low angle of radiation is great for long distant groundwave talking. If you concentrate your signal at a lower angle, it travels farther on the ground before it finally bends (the earth actually curves away from the signal) away from the earth. Secondly, a lower angle of radiation strikes the ionosphere (the part of the atmosphere that your signal bounces off when you are talking “skip” (DX)) at a lower angle, and thus is able to “skip” to a DX station with less hops. For every hop a your signal it has to take, the more its strength is reduced. So, if you are trying to talk to very very distant stations (other side of the earth), low angle of radiation is very very important. Figure 2 shows how a low angle of radiation takes a lot less hops to make it to a DX station as opposed to a high angle of radiation (figure 3).

Figure 2 – The low angle hits the ionosphere at an angle that makes it travel further for each hop. Each hop attenuates your signal a great deal. If you didn’t even know it, this is how signals travel large distances. You can see large areas are hopped over by your signal, it does not just travel on the ground. The ionosphere is charged (given the ability to reflect signals) by the sun (sunspots). This is why skip is influenced by the the sun.

However, if you mainly want to communicate with DX stations that are close to you (DX stations that are say 500 – 1000 miles from you) with the strongest signal, your best bet is to have your antennas lower. A higher angle of radiation (caused by have your antennas low) makes a stronger signal for close DX stations. Keep that in mind when your neighbor with his antenna on his roof crushes you with your Moonraker 4 on a 70 foot tower to a DX station a few hundred miles away. Antenna height plays an important role!

Figure 3 – The high angle travel less distance each hop. You can see, the first hop is much shorter resulting in stronger signals to closer stations (500-1000 miles). Technically, at this high of an angle you signal would be attenuated too much to talk after about 4 hops, so your signal would never make it as far as this figure shows!

When we say that antenna height determines angle of radiation, this is a generalization. This rule holds for all antennas. But, lets say we have a 4 element beam at 40 feet and a 1/2 vertical at 40 feet also. Do these antennas have the same angle of radiation? No, they do not. Actually, vertical antennas have lower angles of radiation than beams when mounted at the same height above ground. Verticals are great DX antennas for this reason (to make your vertical antenna an even better DX antenna read the “Earth Ground” section). Quads have a lower angle of radiation than Yagi’s when mounted at the same height also.

So lets put things in to perspective. What is “high” and what is “low” for 27MHz? Generally for a low angle, you want to get your antenna over 1 Wavelength from the ground (36 feet). Its best to get it up around 60 – 70 feet. If you live on a mountain top, or your home is elevated above the surrounding landscape, you can use the lowest minimum height (36 – 40 feet) because the lower ground around the antenna fools the antenna into thinking its higher and makes a low angle of radiation. Conversely, if you live in a valley where the surrounding landscape is elevated around your antenna, you must go as high as possible (I know that is obvious, but you can’t think if your antenna is 70 foot up in the air you are getting a low angle of radiation – your antenna “knows” its low compared to the surrounding landscape). Now if you wanted a high angle of radiation for strong contacts to close DX stations (500-1000) miles, you can set your antenna about 20 – 36 feet about the ground. Do not go below 18 feet though, because your antenna will start losing its radiation pattern (it will turn into an inefficient antenna).

Article by Scott originally available at http://signalengineering.com:80/ultimate/angle_of_radiation.html

The post Antenna Performance : Angle of Radiation appeared first on IW5EDI Simone - Ham-Radio.