Has anyone tried one of these WARC band verticals? It's supposed to work on 60,30,17 and 12 meters, but the one I've just bought loads up fine on 60, 30 and 17, but shows no signs of life at all on 12M.

MFJ suggested that I ring their technical help people, and when I pointed out the cost of transatlantic telephone calls and that under the circumstances they should ring me (not forgetting the time difference) have gone strangely quiet.

HELP

Phil
G3UGK

It's a pretty simple design. If it tunes OK on 60,30,and 17, it points to a problem with the 12m spokes or loading coil - I'd take a very close look at them. Try checking DC continuity through the coil to each of the spokes.

Steve G3TXQ

Hi Steve

I totally agree; that's what makes it so frustrating. Ive even resoldered the connections to the 12M loadidng coil, tightened up all the nuts and screws, checked for continuity, replaced all the capacity hat spokes...

Any more ideas?

Phil
G3UGK

Have you swept the SWR over a wide band to see if the 12m resonance is there, but shifted in frequency?

Steve G3TXQ

Nothing between 18MHz and 28MHz.

I did remove one of the spokes from the 24MHz capacity hat which should have lifted the resonant frequency, but it had no effect. However, it did significantly increase the resonant frequency of the aerial on 18MHz. I appreciate it would have had some effect on 18MHz because of the interaction of all the capacity hats, but it changed it from 17.60MHz to 18.20MHz - much more than I'd have expected.

Seriously wondering whether the 24MHz coil has the wrong number of turns.

Or something...

Phil
G3UGK

Phil,

I see from the assembly instructions that - within certain limits - you can choose what length you want the radiating element to be. I wonder what yours is?

If that radiator length is too short, the top loading may be insufficient to bring it to resonance; if it's too long, it could already be longer than a quarter-wave on 12m without the top loading.

You can tell I'm now clutching at straws

Steve G3TXQ

The same straws I've been clutching

I've tried it full out and full in - no difference. But I will try again tomorrow with some intermediate settings. (Although it is supposed to work wherever it's set).

Phil
G3UGK

Well I finally sussed it out. It turns out that as supplied, with all the capacity hat radials untrimmed, the 12M section was resonating nearer 17M, thus causing great confusion. I isolated the 12M section by lifting one end of the loading coil and this enabled me to trim up the 17M section which was resonating 3MHz lower. Having got this working, I reinstated the 12M section, minus a couple of radial spokes and managed to get it in the band.

So the problem seems to be that all the supplied radial spokes for the capacity hats are WAY too long, and the initial resonant frequencies on all bands are nowhere near the frequencies to be expected according to the instructions.