Whilst the antenna seemed to work well on 10 metres the SWR was a little high on 20 on the lower part of the band, meaning of course that the antenna was too short. I took the antenna down and after several trips to and from the shack to check the SWR (it must be great to have an antenna analyser) I managed to improve things across the 20m band. The problem was caused by the uppermost clamp not being tight enough, allowing the 20 metre section of the antenna to slide into the main tube thus shortening the antenna! The SWR on 10 is also nicely low, no need for an ATU on these bands. 15 metres has always been a difficult one on this antenna. Indications are that the 15metre section is too long but I have run out of adjustment on that band, if I want to shorten it any more I will have to use a Hacksaw. As it is the match isn't too bad (Around 1.5:1 SWR) but not as good as the other bands. Whilst I was working on the antenna I took the opportunity to connect the ground radials more effectively as pictured below. A good ground system is essential with the AV12 yet the manufacturers don't provide any easy way of connecting the radials. Here I have used the crimp on connectors that slide over the nuts at the bottom of the antenna.
I have an HF analyzer, but it only shows the SWR, thats only half the story, as really I would like to know the impedance vs frequency.
ReplyDeleteGood luck, my gut feel is that you need a better RF counterpoise system to balance the antenna, rather than a 'ground'.
Indeed good weather to work on HF antenna. I think SWR is not that important. As long the SWR is below 3:1 there is no problem. Even with a low SWR the antenna could be worse. Even a dummy load has a good SWR. ;-) Good luck, and let us know what the results are (when propagations will be better) 73 Paul
ReplyDeleteHi Paul and Paul,
ReplyDeleteI didn't make it clear in the blog but I have a system of around 10 counterpoise wires as well as a ground stake. They do make a difference, just as well as it took me many hours last year burying them in my lawn!
73
Kevin
Hi Kevin, It's a hell of a job, but it will benefit your radiation capabilities, that's for sure. Good luck, 73 Paul
ReplyDelete