11M Tiltover Antenna Mast

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

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

The iKeyPad

The Icom series of radios from the IC-746 Pro on to the latest 7800 radios have a 4 memory digital voice and CW  keyer built into the radio. These may be accessed by using the menu to access the keyer, make your recording and using the front panel “F” keys to trigger the individual memories. Sadly, the procedure becomes tedious and rather uncomfortable during a 48 hour contest where you might press the various “F” keys hundreds of times by having to reach across your keyboard, paddle and operating desk. The back section of every Icom manual shows the circuitry for an external keypad. The circuit is consisting of 4 resistors and 4 SPST pushbutton switches and a short 2 wire connection into your microphone plug. Finding a suitable box for the switches is a problem and while looking at an old Apple mouse on the shelf the idea came to me that it’s smooth ergonomic design would be great to have my hand on for long durations of time.

The Apple mouse disassembled with switch holes drilled in upper shell. Lower shell still has circuit board and USB cable attached (All to be removed)

The Apple mouse disassembled with switch holes drilled in upper shell. Lower shell still has circuit board and USB cable attached (All to be removed)

The APPLE Corporation under CEO Steve Jobs were designing some beautiful computer gear years ago and this old mouse was a product of that era.

It was easy to use a small thin bladed screwdriver to lever a few tabs and the mouse fell apart in pieces. Discard the circuit board and USB cable which leaves you with a shell and a base. Find 4 suitable tactile easy to push SPST switch push buttons. The electronics parts suppliers have many types to choose from. The red button is for memory No.1 The quality of the plastic is very good and is not prone to splitting. Start the holes with a small drill bit and slowly increase the size as required. Mount the switches in place and solder the 4 resistors in place. Connect the cable with a 3.5mm plug on the end. Any old old audio cable with the plug attached cut to length will do. I secured the cable in place with a dap of glue from a hot melt glue gun. The inside of the top shell is shown below.

Upper shell with switches, resistors and new cable in place.

Upper shell with switches, resistors and new cable in place.

The upper and lower shell halves should be mated together again. A little super glue will hold them in place if you the tabs don’t align as they should. The finished iKeyPad is shown below.

The completed iKeyPad ready to use.

The completed iKeyPad ready to use.

The next thing you must do is connect a small lead from inside your microphone plug to a female 3.5mm socket so that you can plug the iKeyPad into it. Pin 3 is the resistor nework and Pin 7 is the ground for most Icom radios. The only thing left to do is go into the menu system in your Icom radio and allow the keypad feature to work instead of the microphone scan feature. Another menu item will allow the iKeyPad to operate the 4 memories on both CW and SSB modes. The original Icom circuit of the external keypad is below.

Icom Keying circuit

Icom Keying circuit

Operation is a pleasure. Accessing memories from a keypad is so much easier than pushing buttons on the front panel. The inbuilt Icom digital voice and CW keyer is a pleasure to use. The Icom voice keyer sounds absolutely natural and all audio level parameters are adjustable. Make sure the compressor control is off when you do your recordings. The cost of the iKeyPad is nearly nothing if you can find an old Apple mouse. Of course, any mouse of any brand will also work fine if the housing is suitable and comfortable.

73, Lee ZL2AL

 

Icom PS20 Power Supply Conversion

There are a lot of “orphan” Icom power supplies that you see at the ham car boot sales and flea markets. They usually go very cheaply because they were originally purchased with the Icom 701 and the Icom 720. Both these models of radios have had problems over the years and their owners have moved on. Even though the radios are gone, the power supplies are heavy duty and built to last which is why there are plenty of them still out there. There are two models. The IC PS-701 was the original and it had a large transformer and very good filtering. When the IC720 was marketed, Icom sold the matching PS20 power supply and it is a newer, switch mode design. Even though many cheap switchmode supplies have a bad reputation, the Icom design was very well engineered with the switchmode components in a rugged diecast alloy box with a heat sink on the back. No RFI noise at all with the advantage of plenty of overload protection and excellent voltage regulation. The PS 701 is not really suited as it’s output voltage is 17 VDC unloaded and measures about 15  VDC fully loaded. It could be used if an on board regulator was installed. I have not looked at the internal circuitry of the IC-701 but suspect that the radio has in internal regulator. For our purposes I will only concentrate on the PS20.

I picked up a model PS-20 cheaply a while ago and thought that it would make an excellent power supply for any of today’s modern radios as the design is rated 13.8 volts at 20 amps. The cabinet is well constructed and it has a good quality speaker behind the front panel.

Conversion to a universal supply requires removing the very large DC cable from the back, moving the ground post, installing a pair of terminal posts and putting a switch on the front panel.

The back panel with the new 13.8 V terminal posts install and the Ground post moved to the right

The back panel with the new 13.8 V terminal posts install and the Ground post moved to the right

The original design has one small slide switch on the back panel to sever the line voltage input. The only way of turning on the supply, other that connecting to the Icom radio is the ground the orange wire in the main DC cable via a second switch on the front or rear panel to activate the relay that puts line voltage to the unit. After removing the top and bottom covers the conversion as follows:

1) Cut the rear cable about 6 inches out from the back panel and peel back the outside plastic sheath. This exposes a red and black wires which is the DC output. It also exposes the orange control wire.
2) Remove the ground post and place it next to the AC input connector.
3) Make up a small alloy or steel plate as shown in the photograph with two terminal posts on the plate and mount it where the old cable hole is. You may have to do a pit of filing and trimming to make it all fit. I used 4 x 3mm screws to hold the plate in place.
4) Connect the red and black wires to the two posts.
5) Mount a main Off/On switch on the front panel. I used a small rocker switch and fitted it into the plastic front escutcheon to the left of the LED an the right hand side of the panel.
6) Connect the Orange wire to the switch and the other terminal to ground on the chassis somewhere.
7) Finished and ready to turn on!

The new Line OFF?ON switch installed to the left of the Power on LED

The new Line OFF?ON switch installed to the left of the Power on LED

It is a simple and easy conversion to a quality power supply for a very reasonable price. Photos are attached

73, Lee ZL2AL

Building a Multiband Yagi

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

 

Phillips, Pozidrive and Robertson Screws

Q: What’s the difference between Phillips, Pozidrive and Robertson (square) screws?

A: Philips drive screws are the screws that have cross-slots that look like an X, stamped into the head. Patented in the 1930’s, these were a vast improvement over the antique “slotted” screw, which tended to cam-out easily and were difficult to drive with power drivers.

Robertson (square) drive screws were patented in Canada in 1908 and address problems that the Phillips driver doesn’t quite solve. They allow the screw to be placed on the driver prior to the screw being placed in position. What this meant was that for the first time you could start a screw overhead or in a tight spot without an extra hand holding the screw onto the driver.

Pozidrive screws are the European answer to the Phillips shortcomings. The differences are subtle. At first glance it appears to be a Phillips, but on closer examination you’ll notice a second set of cross-blades at the root of the large cross-blades. These added blades are for identification and match the additional makings on the head of Pozi-drive screws, known as “tick” marks. So the marks are for identification. Identification of what?

Two features of the Pozi-drive screw and driver combination make it unique, and superior to the Phillips. First, the tip or the Pozidrive driver is blunt, which also helps it to seat better into the recess in the screw, unlike the Phillips which comes to a sharper point. This becomes a problem as the tooling that forges the recess in the head of the screws begins to show signs of wear. The recess becomes more and more shallow, which means the driver will bottom-out too soon and will cause the driver to cam-out.

The second unique feature is the large blades on the driver have parallel faces, where the Phillips blades are tapered. The straight sides of the driver allow additional torque to be exerted without fear of cam-out. Knowing this, we can see why a Phillips driver will have problems driving a screw with a Pozi-recess, as a Pozi-driver would have little luck driving a Phillips head screw. One more tip. In a pinch it is possible to drive Pozi-drive screws with a Phillips driver, but you will need to grind down the tip slightly, and expect some slipping to occur.

73, Lee ZL2AL

Pozidrive, Philips & Robertson Differences

Q: What’s the difference between Phillips, Pozidrive and Robertson (square) screws?

A: Philips drive screws are the screws that have cross-slots that look like an X, stamped into the head. Patented in the 1930’s, these were a vast improvement over the antique “slotted” screw, which tended to cam-out easily and were difficult to drive with power drivers.

Robertson (square) drive screws were patented inCanadain 1908 and address problems that the Phillips driver doesn’t quite solve. They allow the screw to be placed on the driver prior to the screw being placed in position. What this meant was that for the first time you could start a screw overhead or in a tight spot without an extra hand holding the screw onto the driver.

Pozidrive screws are the European answer to the Phillips shortcomings. The differences are subtle. At first glance it appears to be a Phillips, but on closer examination you’ll notice a second set of cross-blades at the root of the large cross-blades. These added blades are for identification and match the additional makings on the head of Pozi-drive screws, known as “tick” marks. So the marks are for identification. Identification of what?

Two features of the Pozi-drive screw and driver combination make it unique, and superior to the Phillips. First, the tip or the Pozidrive driver is blunt, which also helps it to seat better into the recess in the screw, unlike the Phillips which comes to a sharper point. This becomes a problem as the tooling that forges the recess in the head of the screws begins to show signs of wear. The recess becomes more and more shallow, which means the driver will bottom-out too soon and will cause the driver to cam-out. The second unique feature is the large blades on the driver have parallel faces, where the Phillips blades are tapered. The straight sides of the driver allow additional torque to be exerted without fear of cam-out. Knowing this, we can see why a Phillips driver will have problems driving a screw with a Pozi-recess, as a Pozi-driver would have little luck driving a Phillips head screw. One more tip. In a pinch it is possible to drive Pozi-drive screws with a Phillips driver, but you will need to grind down the tip slightly, and expect some slipping to occur.

73, Lee ZL2AL

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Spraypainting Homebuilt Radio Equipment

Building homebrew equipment is no easy feat. The “Look and Feel” and the cabinet housings are the problem. I manufacture mine out of aluminium sheet and then spray paint them myself. It’s not difficult to get a professional finish. Here is the steps you must take.

The problem with aluminium sheet is that when it is rolled in the mill it has an oily substance over a smooth surface finish. Basically, paint will not adhere to the surface. I first use a small orbital 1/3 sheet woodworking sander to roughen up the surface. Use 220 grit “wet and dry” auto sandpaper and use it dry. It will take the gloss off the alloy and render the surface with tiny “swirls’ patterns. Then wipe the surface with mineral turpentine to clean it ready to spray. The swirls will disappear when the paint goes on.

Your local auto supply store will have a great selection of spray paint. I prefer Nissan hammertone charcoal grey touchup spray paint. It matches my Yaesu gear and is about $12.00 a can. Pick up a can of etch primer at the same time.

Procedure:
Place the panels or cabinet to be painted in your kitchen oven and bake for about 20 minutes at 40C and use a clean cloth to remove from the oven. Spray on the etch primer. It will hit the aluminium surface and dry in seconds. Put it back in the oven and turn the oven off to bake the primer on and cool down.

While it’s still warm about 35C and the surface is dry to touch, remove the item and spray lightly but evenly with the colour spray. Do not attempt to cover everything the first coat. Wait till it dries and cools and then spray the second or top coat on. You may want to place it back in the oven at 30C for 20 minutes again, turn the oven off and let it cool down. Remove from the oven and leave the item for a few days until the surface is cured and hardened and then you can step back and admire a perfect homebrew paint job. This is an example of what can be done with a spray can and a little ingenuity and your wife’s oven. Note the “reflection” on the top panel

Homebuilt Antenna Tuner

One of the problems with homebrew gear is the lettering. I use “Dekaset” rub on lettering in white to stand out from the black background. It is also available in black for light coloured front panels. If you spray a cabinet, the front panel will have to be a lighter shade of grey to make the letters stand out. After the letters are placed in position, a single coat of polyurethane varnish put on with a tiny artist’s brush will insure that they don’t rub off with use. The finished product will look professional and will enhance the look of your radio shack

73, Lee ZL2AL

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Vacuum Variable HF Tuner

Vacuum Variable Antenna Coupler – by Lee Jennings ZL2AL

Dean Straw K6BV provided the inspiration for this antenna tuner in the 21st edition of the ARRL Antenna Book. I have always liked building antenna tuners and must have built 30 over the past 60 years. They are simple electronically and mechanically elegant devices. Dean’s tuner design took no prisoners.

His design placed the balun on the input side so to prevent heat stress and loss rather the one on the output side. Dean’s reasoning was sound and I decided to build one. Large antenna tuners with traditional wide spaced capacitors can build up very high voltages and the minimum capacity becomes an issue on the higher bands. It was constructed very slowly over 18 months with 12 months on the shelf while I thought about solutions to the problems

Antenna tuners of this capacity made by several manufacturers cost well over $1000 and some of their designs and construction are quite minimal. I made the decision to use vacuum variable capacitors and high quality components throughout.

Main Componenets

Alan of MaxGain Systems was offering 500 pF Jennings “seconds” vacuum capacitors at half price as they wouldn’t meet the 12 Kv spec but would stand 6Kv easily. The EF Johnson rotary inductor, large switches and standoff insulators were found at radio flea markets. A friend donated the large turns counter dial. MaxGain Systems was the source for the two matching turns counter dials and I found the Russian fixed capacitors on eBay. Total cost was around $500 USD. Compared with commercial tuners the cost was substantially less and the performance and ratings was much more.

Front Panel Design

Design plays an extremely important role in how we see objects and how they operate ergonomically. We all see some wonderful examples of bad design in the flea markets. We see boxes with different sizes and shaped control knobs placed in bizarre positions on faded and corroded raw aluminum front panels with little or no lettering to identify what the knobs actually do. Little thought has actually gone into the panel layout by the constructor. Perhaps the unit wouldn’t have ended up in the flea markets if he had thought about it before he built it.

Some considered thinking along with a full size paper sketch or drawing layout working out the problems is easier that hacking away at aluminum and hoping it will work. It usually doesn’t. There are two principles in the design and layout of any homebrew equipment.

1) Balance.This simply means that you strive for placement of a matched set of control knobs equidistant from the edges of the panel in a sort of grid pattern. For example; if the design requires 5 or 7 control knobs then one of the knobs must be in the centre of the horizontal line and the others spaced equally away from the centre one. The same applies for odd numbers. The centre is a space and each knob is spaced from the centre. You can play around on paper until you find the right balance or “look” The idea is simple but vital.

2) Finish. What we see is what stirs us and motivates us to purchase. It is why commercial radio equipment is so successfully marketed.  Multi millions of dollars are spent in the design of radios. Finish, colours and the positioning of controls and buttons is vital when it comes to the overall look and feel of the finished unit. The manufacturer has paid attention to the very small details of his design. An amateur home constructor may not be able to duplicate commercial equipment, however, with a little effort you can turn out a nice looking and well functioning unit.

Internal Layout

Once you have determined where your components are situated on a plan view then it is a simple matter to determine how their controls will project from the front panel and at what level. Dean Straw’s design had a sub chassis spaced  above the floor of the cabinet which meant that the vacuum variables had to be positioned as close as possible to the sub chassis plate and equally spaced from the side edges. The original main roller inductor’s mounting plates were much too high so new brackets were made to bring the inductor height down. The space between the inductor and either capacitor was small but placing the switches at the height of the turns counter dial plates made the controls look “balanced”

Wiring

Internal Wiring to Componenets

I didn’t worry about the wiring inside the tuner. Simple RF wiring practices were followed. Extremely high RF voltages exist but the rule was to maintain a 12mm spacing between any component and anything else. RG213 coaxial cable is good for a few kilowatts inside it’s copper sheath braid. I removed the braid and used the inside conductors to connect the components. When an antenna tuner is in operation at a KW there is a lot of RF floating around in the cabinet so maintaining shield integrity became complicated and didn’t seem worth the effort. To date a flashover has never been experienced even with 1.5 Kw into the unit. I did some primitive testing with odd loads by attempting resonate a 30M loop with 7.1 Mhz and 3.5 Mhz RF. My MFJ RF Analyzer showed some rather very high and very low impedances at those frequencies but the antenna coupler took care of the match nicely. The true test of its abilities is attempting to resonate a 40M dipole on 1.8 Mhz. It did the match OK but I would sure the efficiency would be very poor. The antenna tuner passed its “real world” testing without any component failures.

The original design had a separate inductor for 10m. The reason was that the original air spaced capacitors had a high minimum capacitance which resulted in very few turns on the roller inductor at resonance. I was prepared to add one in if necessary but the 5 Pfd minimum capacitance of the capacitor resulted in resonance on 24 and 28 Mhz with several turns left on the inductor. The SWR measurements into a dummy load showed 1 to 1 SWR on those bands.

Construction

Lower and Upper Cabinet Shells

To construct a metal cabinet is not all that difficult. You do need some metal working tools. A small cheap drill press, cheap 4” angle grinder with 1.0mm thin disc and a good quality cordless drill is invaluable. Hand tools include metal set square, scriber,  2 foot S/S rule, a pair of small “C” clamps and a set of good quality sharp HSS drill bits. If you want to use the counter sunk screws, a counter sink bit, 3mm tap and 4mm tap is required.

Once you have determined the size of cabinet for your project, it would be worthwhile to have the top and bottom shells (3mm thick aluminium) cut to size and folded in a sheet metal shop. The cost is minimal, it will be perfectly cut and folded square. The rest is fairly easy. The top and bottom shells are secured on their sides with 30 x 3mm flat. I simply clamped one on the lower shell. Drill and tapped the holes, put in the screws and then added the top shell and repeated the same operation. Everthing lines up perfectly.

If you choose not to tap the inside plates and angle, you can use nuts and lockwashers to secure them. The uprights are 20 x 20 x 3mm alloy angle as are the top and bottom angles to secure the front panels. Once the basic shell is made, you can measure the exact size of the front and rear panels and have your local sheet metal shop cut them with a metal shear from 3mm sheet aluminum. Drill and tap the front and back panels and the cabinet is complete.

One good source of commercial surplus cabinets are the HP line of test equipment manufactured in the 1960s. They all had that same look and feel with the brushed alloy handles on each side and may still be found on the surplus markets or in flea markets for next to nothing. The cabinets however, when stripped of components are excellent for Linear amplifiers, power supplies and large antenna tuners. It is well worth while hunting down the right cabinet for your project and rebuilding with a new front panel.

Back Panel Layout

The back panel was laid out to match the switches and wiring from the front panel.  Placement of  the SO-239 sockets and feed through insulators are not critical. Although my back panel is not balanced, the sockets are placed in a horizontal line that your eye sees first. The two outside coax sockets are equidistant from the edge of the sides. The feed through insulators and the 25mm standoff insulators that support the sub chassis were all picked up from a flea market for a few cents each. And yes, I washed them in detergent and cleaned them of 70 years grime before installation!

Winding the Toroid

Toroid Details

The ferrite toroid is about 65 or 70 mm in diameter and 25 mm thick. The exact dimensions are not all that critical as long as the mix is acceptable for 1.5 to 30 Mhz. Amidon will have one. There seems to be a lot of mystique about winding a toroid. Before any winding on the form takes place you should wrap the form in two layers of fiberglass tape to prevent the edges of the toroid digging into the wire insulation.

In practice the winding is fairly basic with two parallel windings of 14 turns of #12 gauge Formvar insulated copper wire. After estimating that each of the two lengths of wire would be about 1.3 metre, I put two nails in each end of a long board close together. I wound the ends on the nails which gave me two tensioned wires touching the length of the board. A hot melt glue gun was used to bond the wires together every 50 or 60 mm. I then cut the ends of the wires off the nails, passed the wire pair through the toroid to the centre of the wires and then wound each pair end on 7 turns and adjusted for even spacing around the toroid. An old white nylon kitchen cutting board which I cut up and use for antenna insulators was used for the toroid end disks. I used a 50mm hole saw and cut two disks, one for each side of the toroid assembly. The hole saw leaves a neat 6mm hole in the centre of each disk. Both disks and the toroid assembly are secured with a 6mm bolt, lockwasher and nut to hold it in place on the inside back panel. The four ends of the toroid wires were cleaned and tinned before mounting so that it was easy to solder on the connecting wires.

Finish

The recessed smooth look of the countersunk Unbrako screws – front panel 3mm screws not installed showing the countersinking

Much depends on what we see in front of us and what the final use is. The surface of the panels are prepared with 400 grit wet and dry sandpaper, then cleaned with a solvent and finally sprayed with an aerosol can of your favorite colour on top of an undercoat spray. A good idea is to heat to panels in a kitchen oven to around 35C. Then the aerosol spray will adhere and dry perfectly very quickly. After spray, place the panels back in the oven and turn the oven off and leave it to cool down for a hour or so. The baked on finish will look very good indeed.  Frankly, I find it easier to choose the perfect colour  from the vast array of colours from the automotive industry and take it to my local car painter who will spray it professionally at a minimal cost. Finishing homebrew equipment involves the building and testing to your satisfaction and then completely disassembling the unit and masking before spraying. It is tedious but worth the effort.

Finish also means paying attention to the very small details. Assorted mismatched screws from your junk box really won’t do you any favors with the look of your project. A matched set of screws, either pan head or countersunk Unbracko, Philips or Posidrive will give your cabinet that professionally finished look.

The one final detail is the lettering of the control functions. The first choice is preparing the labels on a computer and printing them on transparent sticky labels. This approach only works if the panel is finished in a light colour so that dark or black lettering will be readable. Unfortunately inkjet printers cannot print labels in white to contrast with black or dark gray panel finishes.

Lettering Finishes the Project Professionally

My choice was to use “Letraset” rub on lettering transfers as I wanted a very dark gray cabinet and front panel. Although difficult to place in position correctly, they do a great job. The letters will rub off again with use unless sealed. Many have tried sealing with a clear plastic spray. Unfortunately the letters will dissolve and your hard work will be ruined. The answer is a very fine artist’s brush and a thin coat of polyurethane varnish which doesn’t react with the lettering. The finished result will add to the project functionality and look.

Summary

The finished design has turned out very well. Hindsight is a wonderful thing but I would have increased the width of cabinet by another 40mm. The reason is purely aesthetic as that would give me another 20mm spacing between each of the turns counter dials so that the switch knobs would look more prominent. The Letraset that I used was 4mm in height. Perhaps I would have used 3mm letters if they were available in white. They are minor changes but would have improved the final design appearance. Paying attention to detail is what home construction is all about.

Thanks to Dean Straw, K6BV for the electrical elegance of his circuitry. This antenna tuner works beautifully and looks great in my shack.

73, Lee, ZL2AL