Category Archives: Antennas

Tube VS Pipe

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Tube VS Pipe In the manufacturing industry one often hear terms such as pipes or tubing. To those working in this industry it is often not clear what the difference is between a pipe and a tube. After all they’re both just hollow cylinders, so many people think that the word has the exact same meaning. That is however wrong. There are a couple of key differences between tubes and pipes:

Tube and Pipe Differences

Tube and Pipe Differences

1. A pipe is a vessel – a tube is structural

2. A pipe is measured ID – a tube is measured ODA hollow cylinder has 3 important dimensions which are: The outside diameter (OD)The inside diameter (ID)The wall thickness (WT) These three are related by a very simple equation: OD = ID + 2 * WT

3. One can completely specify a piece of pipe/tube by supplying any two of these numbers

From the Jan/Feb issue of Branch 68 NZART “Ragchew” Newsletter

11M Tiltover Antenna Mast

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This design actually began when we bought another house and moved about 8 years ago. The house had a patio with a louvered roof supported by the house on three sides and with a wooden 4″ x 4″ square support pole for the far corner. Sadly the support pole was rotting out where it was seated in the concrete. It had to be replaced and I decided that it must be replaced with galvanized square steel section. That idea then morphed into the base of a tiltover mast for a Tri-Bander antenna. The photographs below will tell the story of how the mast was actually constructed. The upper and lower sections of the mast are 6 Metres long and the lower section is 4mm and the upper section was 3mm in thickness. The bottom 3.2 metre support pole is 90mm square section. All three sections were purchased fully galvanized from a local steel supplier. There is about a 2 metre overlap when the upper section is fully extended. There are few specific measurements because the mast was designed specifically for my patio roof support but the basic principles are there. Rough drawings of the rotator mounting platform and the lugs are also shown.

Rough sketch for the mast.

Rough sketch for the mast.

Rotator Platform Details

Rotator Platform Details

 

Details of lug fittings all made from scrap mild steel.

Details of lug fittings all made from scrap mild steel.

Once the lower section was completed, it was bolted to the pergola roof and mounted in place to replace the old wooden pole.

The lower section mounted in place ready for the upper section. Note the 2 logs at the top of the pole where the temporary gin pole is mounted to raise the lower section up ready to insert the hinge pin.

The lower section mounted in place ready for the upper section. Note the 2 logs at the top of the pole where the temporary gin pole is mounted to raise the lower section up ready to insert the hinge pin.

You can see the mount on the top of the pole. You can also see two lugs up near the top of the pole where I attached a Gin pole. This allows me to place the top section of the mast horizontally on the ground to attach a cable from the #2 lower winch temporarily bolted to the base of the lower section. It is simple to wind up the winch and raise the upper section up to the hinge where a 3/4″ stainless steel bolt can be pushed through and secured.

The centre of the upper mast section showing the lifting lug above and the hinge lugs below. of course, all exposed raw steel was painted with galvanizing paint before mounting in place

The centre of the upper mast section showing the lifting lug above and the hinge lugs below. of course, all exposed raw steel was painted with galvanizing paint before mounting in place

 

This is the lower mast pulley at the top of the lower mast. It is of Ocean Yachting grade and NOT cheap plastic as are all the pulleys. The long bolt is only temporary and a shorter one was used in final assembly.

This is the lower mast pulley at the top of the lower mast. It is of Ocean Yachting grade and NOT cheap plastic as are all the pulleys. The long bolt is only temporary and a shorter one was used in final assembly.

Due to the upper and lower square mast sections having a considerable "Gap", we welded in 1/8" "Shims" on the four sides of the upper mast to prevnt a lot of side play and rotation of the upper mast within the lower mast.

Due to the upper and lower square mast sections having a considerable “Gap”, we welded in 1/8″ “Shims” on the four sides of the upper mast to prevnt a lot of side play and rotation of the upper mast within the lower mast.

The upper section is then horizontal and tilted over ready to attach the rotator and mount the antenna. The Gin pole is then removed and the #2 winch cable is attached to the end of the upper section and the mast can be moved from horizontal to it’s vertical position. The winch cable and winch is then unbolted and removed after the upper mast is secured to the lower mast. It isn’t obvious from the photos but the extender cable is routed as follows:  Cable goes from #1winch to top, over the pulley, down inside the mast in the spaces between the upper and lower sections to the bottom pulley, The over the smaller lower pulley and back up to top of bottom section where it emerges and is anchored with a bolt! The smaller #1 winch, when wound extends the upper mast to it’s full 30+ feet in height with about a 2m overlap.

Looking at the bottom of the lower mast with the bottom of the upper mast fully inserted. Not the pulley which allows the #1 winch to crank up the upper section.

Looking at the bottom of the lower mast with the bottom of the upper mast fully inserted. Not the pulley which allows the #1 winch to crank up the upper section.

Although the mast is self supporting, I have attached 3 x 3/16″ nylon guy ropes to prevent swaying in heavy winds. The mast has withstood 120 Kph gusts quite easily over the past few years.

Mast Hinge with 3/4" SS hinge bolt inserted

Mast Hinge with 3/4″ SS hinge bolt inserted. The upper section lifting log can be plainly seen protruding from the upper surface of the upper mast.

I decided to mount the rotator on it’s own platform and sleeve which fitted over the top of the upper mast section. It is simply secured with a couple of bolts which allows the rotator to be easily removed for service.

Rotator and sleeve assembly.

Rotator and sleeve assembly. The #1 winch for extending the mast is shown mounted on the lower mast section. The plate for the #2 temporary winch is shown further down the mast section.

Sleeve, rotator and antenna mast in place ready for a Hex beam. Note the halyard pulleys and shackles ready for mounting and raising other wire antennas and attaching the guy ropes.

Sleeve, rotator and antenna mast in place ready for a Hex beam. Note the halyard pulleys and shackles ready for mounting and raising the other wire antennas and attaching the guy ropes.

The mast originally held a Hex Beam which works well for several years until it fell apart due to the harsh Hawkes Bay U.V. sunshine perishing the nylon cable ties which held the element wires in place. I decided at that point to built a copy of the Force 12 C3S which would be light, cover 5 bands with no traps and would give reliable service for many years. the story of the C3S construction is here Force 12 C3S in another section of this website. The C3S has been a great performer for me.

Original Hex Beam in place on the new mast.

Original Hex Beam in place on the new mast.

ZL2AO and ZL2TJ finishing the mounting of the Force 12 C3S ready to raise in place.

ZL2AO and ZL2TJ finishing the mounting of the Force 12 C3S ready to raise in place.

Mast raised in place with the new copy of the Force 12 C3S.

Mast raised in place with the new copy of the Force 12 C3S.

 

The mast has been an interesting project. I have some basic welding skills but my mate Morrie, ZL2AO is an engineer and knows what must be done to make sure a mast of this size stays intact while raising it and stays in place in high winds. He did all the welding for me.

The final antenna is shown in place in the photos below. Morrie and Carl helped me put the antenna in place on the top of the mast. 36′ elements are a lot to contend with the antenna on the ground in your back yard while trying to avoid trampling plants in your wife’s flower garden!!!! The whole project took a lot of time but not a lot of money. The total cost for the mast was around $650 USD and the C3S yagi was about half that price.

73 de Lee, ZL2AL

Universal Balun

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Baluns may be would in all sorts of configurations to change impedances and change input/output line feeds. One of the two most popular baluns are the 50 Ohm Un-balanced to 200 Ohms balanced configurations. The other is the 50 Ohms un-balanced to 50 ohms balanced configuration. The first balun 50 Ohms to 200 ohms are often used to feed Of Centre Fed dipoles and G5RV and antennas while the second balun 50 ohms to 50 ohms simply provides a match and keeps RF off the feedline. Both configurations require the same initial toroid and windings to cover to HF bands from 3 t0 30 Mhz with little actual loss.

One toroid wound the same but connected differently for two different applications.

One toroid wound the same but connected differently for two different applications.

The photo shows how the windings are wound on the toroid which must be robust enough to handle 1KW and be wound with fibreglass tape to prevent the copper windings digging in on the edges of the toroid and shorting a few windings or arcing into the ferrite toroid under higher power transfer.

The finished toroid Balun ready to to be sealed in it's plastic box and connected into the dipole antenna

The finished toroid Balun ready to to be sealed in it’s plastic box and connected into the dipole antenna. This particular version used 16 Turns of #14 wire evenly spaced around the  T-43 ferrite core. The core was 55mm in diameter and 20mm thick. Amidon in the USA and many other suppliers around the world sell them.

 

 

The finished balun should be put into a suitable plastic box sealed from weather and rain with suitable connections to each leg of the dipole and and with an SO-239 socket for the coaxial feedline.

Baluns are not difficult to wind and are very much less expensive than buying a commercially made unit.

73, Lee ZL2AL

Miracle Antennas

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Over the years every ham has read the advertisements about the various incantations of various types of vertical antennas. “Pick me, pick me, pick me” they all shout. And of course they are backed up with the usual testimonials. Published gain figures are dubious as they are often compared with antennas we have never heard of at locations that don’t exist. Of course we can always search eHam reviews to get a better idea of what any given antenna is like. Even after you have done your research and made your purchase, your results will vary as your soil will be different, your height above ground, whether or not you have used radials and the list goes on. The other variable that cannot be underestimated is the skill of the op. A really good op using a poor antenna will usually outperform an unskilled op using a great antenna. Indeed – mileage does vary.

One local trader on our main NZ trading site is currently listing OCF (Off Centre fed) Windom antennas and making outrageous claims in his advertising pitch to get you to buy his antenna. The vendor suggests that we look up K4(Callsign withheld). I have just researched the DXCC lists and he appears NOWHERE on any recognized DXCC or CQ listings in any mode. If the antenna works as well as he says it does, he would have the plaque on the wall. Surprise, surprise. “Work 200 countries in a weekend” sounds good when you read the advertising copy. It would be foolish to believe that the antenna would do it for you.

At the end of the day, the OCF antenna actually does work OK but uses a bit of jiggery pokery to the lengths of each side and a few well placed ferrite cores to make you think that it is more than a dipole. It isn’t a dipole as we all know! It is a dipole of suspect parentage.

Advertising is advertising. Claims are claims. Our trader is using the same techniques that the purveyors of women’s anti-wrinkle cream use. It is the same language that Proctor & Gamble have used since the last century to sell toothpaste, which after all is simply cream and a bit of abrasive that makes you feel good when you blind the women you are chatting up in the pub. And visa versa.

Over selling radio antennas is the not the sole domain of our trader. Gotham Antennas in the USA sold untold 23′ lengths of aluminium in the 1950s. Man, you were nowhere until you had a Gotham vertical. “Work the world with a Gotham vertical” was the slogan And did it work; just ask the man who owns one. (It did, after a fashion if your put attached radials and mounted it above the garage roof and used an antenna coupler. Sorry, you don’t get that info in the ad!!)

Original Gotham Advertisment in the 1950s

Original Gotham Advertisment in the 1950s

The USA was not the only country that they had the ultra compact answer to the 4 el full size yagi. The Partridge Manufacturing Company in England marketed a 6′ tube wound with wire indoors in the corner of the shack that they said would outperform anything. And of course the testimonials where there on the page to backup their claims. And of course, thousands of hams around the world bought the “Joystick” but there wasn’t much joy after you paid over your money. Just a pain in your bank account.

A home brew version of the "Joystick"

A home brew version of the “Joystick”

An original "Joystick"

An original “Joystick”

So the cry is “lynch the trader, hang em high and bring out the Fair Trade Act”. Being drawn and quartered at least would satisfy our thirst for blood.

Is this going to stop the vendor from printing his advertising crap? I doubt it. What will stop this sort of thing is every club that has newcomers to the hobby making sure that the vendor’s products and claims are well known at club level. Clubs and locals have contacts with most new amateurs and can do that. It comes back to what I mentioned a few months ago about mentoring the newcomers, getting close to them, advising them that antennas can be made that will work well for a fraction of the price.

What I am saying here is to look at the adds, do your research and the ask around in your amateur community for opinions and what they use. It wont be long before you will realize that you don’t get something for nothing in this antenna business. Gain is hard won by plenty of resonant wire or alloy up very high and rotatable.

Complaining about rogue traders in the ham section of eBay or Trade-me and burying your head in the sand with newcomers is not smart which is why these traders survive. They may not get a lot of repeat sales, but he survives. I won’t discuss pricing, as that is a whole new can of worms that I have no intention of opening except to say that every trader must make and is entitled to a profit to stay in business either on turnover or markup. Oil companies do it on turnover and jewellers do it on markup.

At the end of the day… it is and always has been Caveat Emptor. As experienced capable amateurs, we can mentor newcomers and cut down on this sort of trading abuse.

DX IS!

73, Lee ZL2AL

Refurbishing Trap Antennas

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Refurbishing Old Trap Antennas

Hygain, Mosley, Cushcraft and others use traps to get the antenna to perform on several bands. In principal, trap antennas are still a very good compromise antenna for a compact multi-band design. But in time, the traps deteriorate and problems arise. The owner usually buys another antenna and sticks the old antenna underneath the house in a disassembled state where it deteriorates further. At the extreme end you end up with a pile of traps, with no labels or part numbers and with the plastic end caps cracked and quite useless. Worse, you have no idea what frequency that traps actually resonate on and whether they should reside on the director, reflector or driven element.

Trap resonance
The manufacturers rarely design a trap to resonate where you think that they will resonate. A 15M trap that you may think should resonate on 21,200 Mhz will often be designed to resonate around 20.500 Mhz. Why? If the trap resonated in the middle of the band, then extreme voltages would exist at high power levels which will warm the trap and cause arc-overs to damage the trap. When the trap design resonates below or above the antenna design then those voltages are not a problem. You can research the Hygain trap frequencies on the internet. Typically 13.6 Mhz, 20.6 Mhz and 27.4 Mhz are common. Think about it. The length of the elements determine the resonance of the antenna, not the traps! A common trap (if you will pardon the pun).

Trap maintenance
Traps are assembled in the factory and can be disassembled. That’s a given. HyGain put a little dimple in the aluminium outside cover to hold them in place. The dimple may be drilled out and the trap coil will slide out of the outside cover. A little more theory here: The outside cover is actually the capacitor for the trap. The air spacing to the coil is the dielectric, or insulator. After the trap cover is removed from the coil you will see the ends of the aluminium wire joined to the tubes with a set screw. It is almost a certainty that the galvanized steel screw is corroded and the connections will be compromised electrically.

Now is the time to do something about it. Clean the wire loops, clean the tube surface that they touch and fit new stainless self tapping screw with star washers which will bite into the metals and make good contact. Before the coil is slid back in the shroud capacitor, take a stiff brush and clean the trap and end tubes in the kitchen sink with a good detergent. You will have purchased a set of new end caps from the manufacturer and now the traps may be re-assembled good as new.

There is a drain hole in each shroud. Make sure they are facing down when the antenna is up on the tower. A trap full of water will cause major embarrassment to the owner and is a source of great amusement to the next door neighbour when it is on fire! If you decide to use a balun, be aware that the standard HyGain BN-86 balun is not a good choice if you run 1 KW. They fail. They are fine at 500W. They should be mounted BELOW the boom, not above. And make sure you enlarge the drain holes when you check the internal soldering connections.

Trap Resonance
I have already discussed resonance above, but how do you determine it’s resonant frequency? The shroud, being a capacitor of under 50 Pf in value is very susceptible to surrounding objects which will detune the trap. The best way of measuring a trap frequency is to tie a loop of thin nylon fishing line around each end tube of the trap and hang it from the ceiling so it is in free space about stomach level ready for measuring. Then use your grid dip meter with its coil end on to the end of the trap tube about 10 or 15mm away. You may find that only one end will give you a resonant dip. take several measurements and get a precise average.

Don’t hold the GDO. Stack some boxes or a chair or whatever to get it in that position so you don’t have to hold it. You simply have to adjust the GDO looking for the dip. And it will be a challenge to find the dip because the “Q” of the trap assemble ywill be around 300 and the dip will be minuscule and very sharp and very easy to miss. Eventually you will find it. Write the frequency on the shroud with a pencil and move on to the next one. You will eventually will have 6 traps in pairs. Some traps will have different end tubes on them and you will know where they go. Download the manual and study it. Eventually it will make sense and you will be able to sort out what the trap is you have in your hand that has no label.

Antenna re-assembly
Where tubes fit into each other and fit into traps, the aluminium must be cleaned and shine for a good electrical connection. Elbow grease and steel wool will do the job. The insides of the tubing may be cleaned with a round file or a rifle bore cleaner. Old tubing clamps should be disguarded and replaced with new stainless steel clamps. Finally, a very fine coating of UTILUX jointing compound (Most electrical wholesalers have it in stock) or the like should be applied to the tubing surfaces before clamping.

An antenna refurbished and repaired in this way will give many more years of service. I have refurbished several HyGain TH3s, TH4s and TH6s this way and they worked as good as new.

73, Lee ZL2AL

Rebuilding Aluminium Antennas

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I’ve rebuilt a lot of HyGain and Mosely antennas over the years and recently built a copy of a Force 12 Tribander from assorted scrounged corroded tubing. Aluminium corrodes over time and it’s a problem. There are a few things that you can do to take the work out of corroded tubing.

1) Most hardware stores and some engineering supply companies have a 3M product which fits into an electric drill chuck. The abrasive wheel part is a course raspy hard synthetic wheel designed to remove paint. It comes with it’s own arbour shaft and the abrasive wheel is about 120mm diameter and about 30mm thick. It takes all the work out of restoring the outside of any badly corroded alloy tube. One wheel will last long enough to restore the shine to most 3 or 4 el.

2) The second problem is cleaning the inside end of tubing. You just can’t get at it easily and you need to so that good quality contact is made with the next tube that slips inside. I solved the problem by going into a gun shop and buying 2 brass wire brush rifle pull throughs normally used to clean barrels. They are about 90mm in length with brass bristles and have a 1/4″ shaft. The small one will clean the inside of 3/8″ up to about 5/8″ tubing. The larger one for a 12 gauge shotgun does the larger tubes. To use them, I soldered on a 6″ long, 1/4 dia shaft extension onto the pullthrough shaft and put the shaft in a cordless drill running at slow speed. it works a treat and the tubing insides are sparkling clean!

3) For the past 20 years i have used a electricians conduction compound made by Utillux It’s P/N is H-2397 Jointing Compound. It preserves and conducts between the metal tubes. Brilliant.

4) I don’t rely on clamps any more. Although I use them and tighten them, I also use 1/8 Pop rivets in the same way that Force-12 do to secure the elements in their antennas.

5) Have a look at /3219/building-a-multiband-yagi/ on my website and you will see some ideas for clamps. The standard muffler clamps drove me crazy for years. I don’t use them now. I don’t have to endlessly pull the antennas down re-tighten the clamps any more and the elements stay where they should be for years.

73, Lee ZL2AL

Building a Multiband Yagi

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When you are a new ham it doesn’t take very long until you realize that DXing on the higher bands is a tough ask if you only have minimal wire antennas. Over the years I have had many commercial antennas including the classic HyGain 204BA and the HyGain TH6DXX. These are very big antennas which require very big towers to hold them up. A few years ago it was time to move to a smaller residence and the TH6DXX had to go. Our new property has a smaller footprint which limited the size of the antennas. I struggled to break the pileups with a small mast and trap dipole and decided to build a 35 foot telescoping mast with a small yagi on top. I decided to build a copy of a very successful commercial antenna which utilized 2 elements each on the 10M, 15M and 20M bands. It also worked on 12M and 17M with unity gain. This particular antenna design has no traps and the 6 elements were interlaced on the 14 foot boom. The 20M driven element is fed and the 10M and 15M elements are closely sleeve coupled to the 20M element which meant that only one feedline is used. The design appealed to me. The write-ups on eHam looked good so I started accumulating used aluminium tubing for the project.

Unexpectedly, a local ham generously offered me a Hex Beam which was smaller, lighter and basically was a two element yagi on each of he HF bands. It had nearly the same specs as the yagi I was about to build. I accepted the offer and with the help of some local hams it was up on top of the new mast. The HexBeam worked very well indeed. My DXCC totals on 12M went from 42 entities to 187 in 18 months. I could work most of the DX that I could hear. Although I wasn’t the first to break the pileups the Hexbeam worked quite well. My amplifier helped of course. Over the 18 months it was up we had several robust wind storms. Nothing of hurricane force hit it but one day I noticed a wire hanging down. I also noticed that 10M didn’t work very well and was tricky to use even with the tuner. Over the past 6 months, more wires separated from the spreaders and are hanging down.

Existing HexBeam with wire elements in disarray

Existing HexBeam with wire elements in disarray

Strangely, the antenna still works on 20M and 15m but the performance is off to say the least. The other problem is that when I feed power into the antenna, the SWR fluctuates and the amplifier protests. I made the decision to carry on building the new yagi. It seems to me that solid aluminium tubing will probably stay up longer with fewer problems. I dislike disconnecting wire dipoles and loops from masts and lowering antennas to change them.

Element construction
I cannot believe how much aluminium tubing is stored under ham’s houses, in their back yards or in garages. Used aluminium tubing works just as well as brand new tubing. It simply has to be cleaned up. As I started this project I sourced much of the tubing that way. In metric countries like New Zealand, new tubing is supplied in metric sizes. Many old antenna designs and old tubing lying around is in Imperial size. The two sizes are generally not compatible for sections to slide into each other. The equivalent size of 1 inch in metric is 25.4 millimetres. And if you wish it to slide into the next size up it will be .4 mm too large and won’t fit. Generally a tapered element consisting of sliding tubing must be all metric or all Imperial size. You may have a metric sized Director and an Imperial sized Reflector.

This particular antenna design uses 25mm (1”) tapering down to 10mm (3/8”) sections in 1.2 metre (4 foot) lengths. That is very convenient as the new lengths come in 4.8 metre (16 foot) lengths from the factory if you choose to buy new and you get 4 sections from each full length. The surface of old aluminium tubing is a bit of a challenge to clean up. A little fine emery cloth (240 grit) or steel wool will do the job quite nicely. Cleaning the inside of the tubes was a big problem until a friend suggest rifle cleaners. The rifle cleaner is 10mm diameter and has about 3 inches of brass bristles along it’s shaft. The shotgun barrel cleaner is about 1 inch diameter for larger tubing. I soldered a 6 inch brass shaft on to the cleaners and used a cordless drill to ream and clean the inside of the old corroded tubing. The result is magic and finished in a few minutes! You can see the result in the photo below.

The element packs and boom made from new and used alloy tubing.

The element packs and boom made from new and used alloy tubing.

The elements are cut to size, measured, double and triple checked for correct measurement and each element is bundled and taped ready for final assembly. Each element section is “pop riveted” into the next section with two 1/8″ pop rivets. I also used conductive grease for each joint. Each element is in 3 sections. The centre section is clamped to the boom and each of the 2 outside pop riveted sections are inserted into each end of the centre section. The outer two multi tubed sections are hose clamped to the centre section to allow for final adjustment. It also allows easy assembly on the day of placing it on the mast or tower.

Element to Boom Clamps
I managed to find a old “U” shaped piece of aluminium that looked like it would be perfect for the right angle clamp side pieces.

angle pieces cut from scrap aluminium

angle pieces cut from scrap aluminium

The material was 3/16” thick and high tensile alloy but was large enough to make five sets of clamps. All I had to do was buy a section of 3/16” x 3” x 10” flat plate and cut sections for the element support plates. All cutting was done with a hand jigsaw fitted with a good quality metal cutting blade.

Cutting the plate

Cutting the plate

The cut leaves the alloy a bit rough but it is easily cleaned up with a small hand grinder with sanding pad or a file may be used. The boom was exactly 2.0” diameter so I set up a length of scrap 2” square steel section, clamped the side angle pieces in place and then clamped them to the top plate. The square section may be seen in the photo along side angles that were just cut. The “G” clamps held the angle pieces and the top plate together while the four 3/16” holes were drilled. The 3/16” pop rivets held the whole clamp together ready to be pop riveted to the boom.

Finished Boom to element Clamp

Finished Boom to element Clamp

This antenna design called for 2 full size elements for each band. The 20M driver element was split in the centre and made a bit differently with a longer support plate. Each element was electrically insulated from the boom with sections of plastic electrical conduit slipped over the element middle. The photo below shows all six finished element clamp assemblies sitting on the boom.

Six elements sitting temporarily on the boom before being moved into place and riveted

Six elements sitting temporarily on the boom before being moved into place and riveted

Making the Driven Element
Feeding a Yagi with power while obtaining a good match for the radio has always been a problem. Over the years Gamma matches, Hairpin loops, Delta matches and other methods have given way to 50 ohm coaxial cable feeding the split driven element through a balun. The split element needs some type of insulating rod at the feed point into the ends of the two tubes. I could have bought a small length of fiberglass tubing, but a local store was selling fibreglass handled hammers cheaply and they would do very nicely.

Cheap Hammer!

Cheap Hammer!

The handle was covered in rubber but with a little work with a small grinder, the fibreglass centre support took shape and fitted into the tube ends.

The Fibreglass Centre Rod emerges

The Fibreglass Centre Rod emerges

Rod inside tubing ends and split PVC spacer in place

Rod inside tubing ends and split PVC spacer in place

A couple of bolts to attach the balun and some weatherproof sealing tape finished it off and it was mounted on it’s clamp plate ready for connection to the balun.

The finished split driven element ready to go into DX battle!

The finished split driven element ready to go into DX battle!

The photographs tell the story. In retrospect, a correctly sized fibreglass tube would have been easier.

Balun Construction
Baluns come in all forms and sizes but sometimes the simple coil of coax cable works very well indeed. Many articles have been written on the diameter and the number of turns but I settled on 6 turns about 5 “ diameter and wound them inside an old plastic tube. The data is from an article written by Ed Gilbert WA2SRQ

The Completed Coaxial Balun Place

The Completed Coaxial Balun Place

I have used this type of Coaxial Balun previously and it works very well. Most articles on balun construction suggests that winding the turns over a short piece of PVC is the way to go. Winding the turns inside the tubing is much easier and the naturally slide into place. And then the turns are secured in place with plastic cable ties. I made up a clamp from thin scrap aluminium which is held in place with 1/8″ pop rivets. The balun is virtually immovable. Connections to the driven element are sealed with amalgamating sealing tape to prevent moisture creeping back down the coaxial cable. This system worked well for me on another similarly constructed 20 metre yagi I built a few years ago and I have used it on other similar antennas.

Mounting the Elements to the boom

Drilling the rivet hole in the boom. Note the F Clamp at the back holding the assembly in place

Drilling the rivet hole in the boom. Note the F Clamp at the back holding the assembly in place

The next stage of mounting the elements is not all that difficult. I clamped the boom in the jaws of a work table ad then marked where the elements would be mounted. I check the measurements again and then again a 3rd time. I placed one of the 20M elements on the boom and clamped it so the bracket wouldn’t rotate as you can see in the photo. It was a simple matter to drill out the 1st 3/16″ rivet hole and fix the rivet.

The 2nd hole was on the other side angle and it was riveted. Now in place, the clamp couldn’t move and the remained holes were drill out with the cordless drill and the clamp was secure.

The photograph below shows the three close spaced driver elements mounted on the boom and their angle plates riveted.

10M, 20M and 15M Clamp Assemblies with insulated elements

10M, 20M and 15M Clamp Assemblies with insulated elements

 

The mast to boom plate was made from an old used piece of alloy “U” section. The section it wide enough on both sides to fix a pair of 2″ “U” bolts in place to hold the mast and boom together. One of the problems with “U” bolts and muffler clamps is that the mast or the boom will, over a period time start to rotate within the clamps. If you tighten the clamps you end up on a never ending spiral of constantly tightening the nuts on the U bolts which will distort the mast or the boom. This can easily be prevented with a single 3″ bolt through mast and plate. Another is placed through the boom and plate. This absolutely prevents rotational movement and the U bolts do not need to be tightened beyond limits. You can see the whole assembly below.

Mast to Boom section plate with long bolts to prevent rotation. The small holes on the boom are there as the boom was previously used in another application.

Mast to Boom section plate with long bolts to prevent rotation. The small holes on the boom are there as the boom was previously used in another application. NOTE: The “Mast” marking on the horizontal tube actually marks the centre of the mast placement. The vertical tube is the mast and horizontal is the boom section.

Time to Finish the Project

During the past week, the mechanical parts of the antenna were finally finished and it was ready to erect. Morrie ZL2AO and Karl ZL1TJ came over to give me a hand (More than a hand actually!) to pull down the old Hexbeam and replacing it with the new Tribander. The mast is a tilt over design that I built a few years and in very short time it was lowered over with a winch . A second winch allows the top section of the mast to be wound down about 20 feet into the lower section which makes life a bit easier. Karl and Morrie wrestled with the old Hexbeam until it was on the ground.

The Old Hex Beam being removed.

The Old Hex Beam being removed.

The Hexbeam actually failed because the plastic cable ties which held the hose clamp and wires to the fibreglass rods. I suspect that the failures occurred because of the 2400 hours a year of sunshine we get in this area of New Zealand.

We assembled the rest of the driver elements and stood the 12′ mast up vertically to mount into the antenna rotator.

The 3 Driver elements in Place

The 3 Driver elements in Place

All was going well so we cranked the mast off the ground and placed all the Reflector elements in place, did some final mechanical checks and it was ready to winch up to vertical. We cranked it up at about 25 feet and looked at the SWR and it was excellent on 20M but 500 Khz high on 10M and 200 Khz high on 15M. Various discussions centered around “we should do this with a calculator” and one was soon on the table with much head scratching etc. I made the call to wing it and pulled out the 10M DE by 4″ and the 15m DE by 2″ . Feeding the yagi through an 80 foot length of RG213 good quality cable showed the following results after the element length adjustments. 20 metres came in at 1:1 and 50 ohms at 14,152 Mhz The results were excellent with SWRs of 1.1 at 50 ohms on all 3 bands and just where I wanted it.

17M and 12M are a different story and need to be dealt with at the shack end. A few years ago I built a vacuum variable antenna coupler that will match almost anything. A few minutes winding turns counter dials and both 17M and 12m were able to be matched to the transmitter. NOTE: That does not change the SWR on the line. it simply allows you to use the antenna on those bands with power losses. In fact, 17M and 12M work rather well as a high dipole with unity gain. You couldn’t do the same thing with a typical trap tribander as the traps get rather warm working on bands they are not designed for.SWR Readings When you build an antenna from a patterned design you really cannot predict how it will behave in real life. An antenna analyzer doesn’t give you the whole picture either. You actually have to use it on the air to get a “feel” of how it performs. We cranked up the antenna into position at 35 feet and it was ready to have a listen. I was hearing a few signals on the bands but high noon in ZL is not all that exciting. Looking at the cluster there was a bit of DX around.

In place ready to go!

In place ready to go!

A few spins of the rotator on various sigs showed that the F/B looked good at a couple of S-Units and forward gain was just under an S-unit. It some very steep nulls off the sides. What I was experiencing is about what the design parameters had predicted for this antenna. I had a look at the cluster (around 0100UTC) and 9L1A was on 28,029 about 549 with a very smart op on the other end. With a rush of blood to the head I fired up the Alpha and gave him a call. The second call got my report and he was in the log and a big grin on my gob. Throughout the rest of the afternoon and evening I cruised the bands and made plenty of contacts at will. Even marginal signals were reasonably easy to work. My log is below.

My Logbook for the Afternoon.

My Logbook for the Afternoon.

The antenna’s performance is very satisfactory. It is not a pair of stacked 204BAs. It was never intended to be. It is a light, easy to handle design that offers good performance on 20, 15 and 10M and is basically a high dipole on 17 and 12M.

Finally up in place. Lean, Mean and NO TRAPs!

Finally up in place. Lean, Mean and NO TRAPs!

Nevertheless it works very well and has directivity. The joy of this antenna is that I will never have to worry about traps failing. It will also handle any power from my Alpha amplifier with ease.

The Antenna in Place up 35'

The Antenna in Place up 35′ The pole in the foreground supports my 30M full wave loop and the end of the 80M/40M Trap dipole

Since most of the materials were mostly salvaged from old alloy tubing and angles. Anything that I couldn’t find had to be commercially sourced the final cost was about 15% of a new Force12 C3S imported into New Zealand.

This is the end of the project and I am not sure what will follow next year.

73, Lee ZL2AL

 

HF Antennas & Feeder Lengths in Metres

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This handy chart was developed by Gary, ZL2IFB. It is a very simple way of finding out what length of wire you need for your particular frequency. Thanks Gary!

Band CW SSB ¼ wave ¼ – 5% ¼ x 0.66 ½ wave ½ – 5% ½ x 0.66 Full wave F – 5% F + 10% F x 0.66
160m 1.825 41.07 39.01 27.38 82.13 78.03 54.76 164.27 156.06 180.70 109.51
1.850 40.51 38.49 27.01 81.02 76.97 54.02 162.05 153.95 178.25 108.03
80m 3.520 21.29 20.23 14.19 42.58 40.45 28.39 85.17 80.91 93.69 56.78
3.800 19.72 18.74 13.15 39.45 37.47 26.30 78.89 74.95 86.78 52.60
40m 7.025 10.67 10.14 7.11 21.34 20.27 14.23 42.68 40.54 46.94 28.45
7.100 10.56 10.03 7.04 21.11 20.06 14.07 42.22 40.11 46.45 28.15
30m 10.105 7.42 7.05 4.94 14.83 14.09 9.89 29.67 28.18 32.63 19.78
20m 14.020 5.35 5.08 3.56 10.69 10.16 7.13 21.38 20.31 23.52 14.26
14.250 5.26 5.00 3.51 10.52 9.99 7.01 21.04 19.99 23.14 14.03
17m 18.075 4.15 3.94 2.76 8.29 7.88 5.53 16.59 15.76 18.24 11.06
18.120 4.14 3.93 2.76 8.27 7.86 5.51 16.54 15.72 18.20 11.03
15m 21.020 3.57 3.39 2.38 7.13 6.77 4.75 14.26 13.55 15.69 9.51
21.250 3.53 3.35 2.35 7.05 6.70 4.70 14.11 13.40 15.52 9.41
12m 24.900 3.01 2.86 2.01 6.02 5.72 4.01 12.04 11.44 13.24 8.03
24.950 3.00 2.85 2.00 6.01 5.71 4.01 12.02 11.41 13.22 8.01
10m 28.025 2.67 2.54 1.78 5.35 5.08 3.57 10.70 10.16 11.77 7.13
28.500 2.63 2.50 1.75 5.26 5.00 3.51 10.52 9.99 11.57 7.01
6m 50.100 1.50 1.42 1.00 2.99 2.84 1.99 5.98 5.68 6.58 3.99
52.050 1.44 1.37 0.96 2.88 2.74 1.92 5.76 5.47 6.34 3.84

Where a full wave in metres = frequency in Hz divided by the speed of light (299,792,458 m/s)

Reduce dipoles by ~5% for end effects. Add 5-10% to full wave loops. Trim all antennas to resonance.

Lose one third physical length for velocity factor of typical coax. 73 de ZL2iFB