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The main source of inspiration for this project was found <Here>
This antenna cost very little money, as all the parts were either in my junk box/collection of bits and pieces, or obtained from boot sales and charity shops.
My objective when building this antenna, was to have a portable HF antenna that would be light to carry and quick to put together. This could then be used when going on my camping and caravanning holidays, as well as some field day trips.
The antenna was initially designed for 80 meters, though I hope to
use it on 40 with some experimentation with coil taping points and changes in counterpoise.
In order to keep all the necessary parts together, I made a bag out of some surplus caravan awning skirt stitched together on the XYL sewing machine. (Don't tell her!!)
While at a local Sunday morning boot sale I came across some aluminium tubes that screwed together in order to attach a squeegee for cleaning upper floor windows. These were just what I needed for this project and the handing over of three pound was all that was needed to secure them.
The top sections of the antenna were made from two lengths of 8mm diameter solid aluminium dowel that I had among other bits and pieces at the back of the garage. At the end of one length I tapped a thread so that this could be screwed into the top of the loading coil. However when assembled it was found that when screwed in tight it still tended to wobble a bit, therefore I looked for a way to make this joint stronger. Hence the use of a counter weight taken from a record turntable arm I dismantled many, many, years ago. I tend to keep all sorts of strange bits and pieces just in case I’ll have a use for them one day. This item had been in my tin of nuts, bolts and odds and ends for more than 40 years. Finally, I found a use for it. The day you throw something away, you can be sure, will be the day you regret later!
To join the two top sections of the antenna I used a bolt spacer made of aluminium. This I cut along its length with a hacksaw and together with a jubilee clip, secured to the other end of the first top section. The final to section could then pushed into this and the clip tightened up.
The lower sections of tube that already had the threaded plastic connectors were further strengthened with an outer sleeve of tube cut from an old pair of crutches acquired from a charity shop. These pieces were held in place on one half with a pop rivet.
On the other ends, four slits were cut down the tube for about 20cm and more jubilee clips fitted. Then the end that fitted to the base of the loading coil had a metal cap with a bolt in the centre, pop riveted onto the end, which then screwed into a thread at the bottom of the coil.
Another lucky find while enjoying a stroll around a local boot sale was that of a very thick walled piece of plastic pipe and a big aluminium box with toroidal transformers, power transistor’s and some very thick aluminium plates (6.5mm) acting as heat sinks. The wiring was old rubber coated stuff and in a mess. However I was sure the parts would come in handy sometime. For £2 I felt this was a bargain and knew it would not be long before I would find a use for some of these parts. Well the tube proved ideal for the loading coil of this project and the thick plates were used to cut the discs for the top and bottom of the coil in which I tap treads for the elements to screw into.
Wire salvaged from some speaker crossover filters, was used to wind the loading coil.
The former was made ready for the wire by first sticking four pieces of double sided tape the length of the former, spaced out evenly. This was done to hold the turns in place and stop it slipping, keeping the turns neat.
The winding was best achieved by putting a cut off bolt, the same thread as that tapped in the coil former end plates, and fixing the former to the drill. Then placing the drill in a vice and operating the drill at a slow speed while allowing the wire to run of the spool with enough tension to keep it tight on the former.
The start and end of the winding being secured with solder to tabs fixed under bolts that secured end plates to tube/former.
I wound as many turns as could be accommodated on the length of tube I had. Although my original intention was to make this antenna for 80 meters, I hoped to make some arrangement for multiple taping point and additional counterpoise lengths in the future. This would then hopefully give me 40M and 20M, but possibly even 160M.
Note in the picture to the side here, one of the four lengths of double sided tape stuck to the tube to hold the turnes in place.
The antenna feed point is 50cm of the ground and insulated from it by using PVC wast pipe for the bottom section of the antenna. A BNC socket and small banana plug socket were fixed into a pipe joint for easy access for soldering connection to the sockets.
The wire seen here in the picture opposite is fixed to the bottom of the antenna inside the PVC pipe section with a solder lug and pop rivet. This wire then passing through the pipe joint to the BNC socket. The braid side soldered to the banana plug socket for easy attachment of a counterpoise.
Fitting the sockets into a PVC waste pipe joint allowed easy access to the sockets for soldering.
In order for the bottom section of aluminium tube to fit snugly inside the PVC pipe, a second short length of pipe was reduced in diameter by cutting out a small slice along its length, so that it could be squeezed to fit one inside the other, the aluminium tube was then fitted inside them both.
At the other end, four cuts were made down the Aluminium tube for about 20mm and a jubilee clip fitted.
Teeth were cut in the bottom of the PVC pipe to prevent the bottom of the antenna kicking out when guyed down.
A simple balun was made in the popular method, of winding several turns of the coax around a torrid. In the case, an old TV line transformer yoke was used.
When complete the assembled antenna was erected in the garden and length of wire for a counterpoise was plugged in at the feed point. Using an analyser I then set about finding the taping point on the coil which gave the lowest possible SWR. Experimenting with the length of counterpoise also improved this and a SWR of 1.5 and impedance of 50 ohms was achieved.
Assembled antenna with the coil tapped at the point which resonated the antenna on the 80 meter band, favouring the CW portion.
In order to give the antenna an on air test I connected up my Sparford 80 meter CW QRP transceiver which puts out about 1.5 watts and managed to make a short contact with a G3 station in Tiverton. My signal was not very strong and I was eventually lost in the noise, however I was still pleased with the result of just 1.5 watts into what is a compromise antenna.
On another one of my many Sunday visits to the local boot sale, I picked up a real of parachute cord and some large offcuts of various sizes and thickness of Perspex and nylon. These materials were perfect for making the guy lines and tensioners as well as a centre anchor point for the four guys.
Staying in our caravan at Passage Farm Nr Arlington on the River Severn and playing radio.
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