June 27th, 2009 by g4lds
Having recently moved to Morecambe (Good Move!!), I had my dreams of a 80 foot tower with a rotary HF beam popped as the garden is only 25 x 35 feet!!! MMM Back to plan B. Which is wire aerials that i have used to good effect in the past.
Doublet for 80 - 10 fed by balanced feeder
The doublet works I found on all bands. A dipole is really a one band aerial, cut for 1/2 λ on the band you want to work on and fed by 50 Ω coax (really it should 75 Ω as that's the correct value of a 1/2 wave dipole but rigs are 50 Ω!!) A doublet is a balanced aerial around 1/2 λ on the lowest frequency you wish to work on however in practice, it can be 85% of this value with minimum effect of efficiency. I find that a top of 84 feet (ie 42 x 2) is good for 80m upwards. I fed this by 300 Ω slotted ribbon cable. It can be feed by open wire feeder between 300 - 600 Ω shop brought or homemade.It should be fed into a balanced Aerial Matching Unit (AMU or called ATU) or to a 4:1 or 6:1 Balun to coax. I have used this both Horizontal and Inverted Vee. During a contest on 40 meters I managed to work Stateside using this at 15 feet!
Another aerial which I have used is the W3EDP. This appears to be in use from around the 1930s. Check on the net for its history. This can be laid out in really any layout with bends, kinks and it still works! It rocks on 5 Mhz as using 5 watts I have covered round the UK no problem. It again should be fed to a 4:1 balun before the AMU or a balance Z-Type AMU. Very useful for portable use, laying along a hedge, thrown up a tree.
This should be feed via a balanced AMU like a Zee match or via a 4:1 balun to an unblanced AMU. If using a balun, the long length goes to the "hot" terminal and the short to the "earthy" terminal. The notes indicate that on 3.5 Mhz, the counterpoise does not need to be connected(it acts as a endfed around 19 feet longer than a 1/4 λ), 7Mhz its a halfwave with eightth wave feeder, 14Mhz its a fullwave endfed beyond the end of the counterpoise 17', 21Mhz its one and a half wavelengths with the 17' counterpoce acts as twin feeder! 28Mhz it does neeed the counterpoise as it two and half wavelenghts long (85')
Now having used these aerials at my new QTH, I found that the local noise was producing a S8 level on HF so operating was not very successful!. My thoughts turned to going portable in the wonderful countryside and sea front around Morecambe.
Non counterpoise aerial (See table for variants)
I had read early about the non-counterpoise aerial on the G-QRP forum. A couple of years ago, you could buy a version of this aerial from Stateside via E-Bay. There has been lot of thought of what this aerial is, I think it looks and works like a "J" pole, or a Zepp or even an Off Centre Diople. A lot of work has been carried out by Pete M3KXZ (see www.outsideshack.com
) and also look on the wonderful Cebik site http://www.cebik.com/content/a10/wire/m3kxz.html
Table for different coverage
After reading up the published info and mailing Pete, i thought that this might be worth a try. I decided to build a 20-6 metre version. I cut a length of speaker cable (or called low voltage twin cable) 12.5 feet long, and a length of 24/0.2 connecting wire 12.5 feet long. I soldered this single wire on the end of one of the twin cables, making note that this would be the "hot" or radiating element. I then used insulating tape to cover the joint and to "weatherproof" the cut ends. I then wound 10 turns on a ferrite core to act as a 1:1 balun or RF insulator at the "feed point" of the aerial. I then used insulating tape on the soldered joints and to avoid the winding moving, I used Tye-wraps.
1:1 balun or feedpoint for my portable non-counterpoise
Having made this I connected around 10 feet of twin cable to act as ribbon feeder to an AMU which had a 4:1 balun built in. Having used my aerial analyser, checked that it could be resonated on 20 - 10 meters using the AMU, noting the settings. I then connected the FT-817 to see how it worked and found the noise level had dropped to S1 and signals were heard! A rush into the shack and the noise level was still S8 so the non-counterpoise was connected via a coax lead to the shack, and switching between the two aerials, the noise was there or not depending on the selected aerial!!! I moved the non-counterpoise aerial near to the house and the noise level shot up. So a quick re-think took place and I made another version for the base station, using a 4:1 balun at the feed point so I could use a direct 50 Ω coax feeder to the shack.
4:1 balun feed point of my base version of the non-counterpoise
My base version is set up with the feed point on the fence and sloping towards the house, which blends in with the rest of the domestic site. Currently the noise level is around S1-2, I am able to work on 20m upwards. During recent sporadic E openings on 10 meters, I worked from North to South Europe. Later I tried the portable version on the stone jetty here in Morecambe, wound helically around a 6m pole, I heard around Europe and Stateside on 20m. (would have tried longer and maybe tried working but the batteries went on the '817!
My next plan is to make a 50 foot version for operating on 40 meters upwards but firstly I need to find out the local noise one source is from the street lights and I hope to get the local authority to find the cause. the other local
- My portable version wound on a kite winder
source I hope OfCom will help in deaing with.The next version, I may make from 300 Ω ribbon cable as it may be more weatherproof!
UPDATE (28 July 2009)
Have re-read the notes and replaced the 4:1 balun with a 1:1 choke ( 8 - 10 turns on a ferrite bead) and will try this out now. First tests make it seem a bit "more lively!". When can afford it! will replace this with 450Ω ribbon as it should decrease the losses
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