Dear J.B., LF group,

>Dear J.B., LF Group

>I think the problem here is the size of the coupling loop, which is only

>slightly smaller diameter than the main loop.

Hi Jim, LF Group,

My antenna is based on the successful design by Steve, VE7SL, with

only two differences, 1) my pickup loop is shielded, and 2) I used #12

wire rather than #20. Could those two differences make that much of

a change in the loop operation? I know that all other things being the

same, using the larger gauge wire would have raised the Q, but would

it change things so drastically that I'd have to use a smaller diameter

pickup loop?

Steve suggested that I use a simple non-shielded pickup as he used

on his antenna. I tried that, but I found little or no difference between

it and my shielded pickup. Both where spaced about 6 inches inside

the main loop, just as on his antenna, which works fine. That's what

is puzzling me, why does it work OK for him but not for me??!!

I don’t think the alterations in loop construction would make a major difference – the loading of the loop is not very critical provided it is in the right area, changes in Q will make some difference, but not a huge difference. There are other things that can make a big difference. One is receiver sensitivity – loops produce relatively small output so require an RX with good sensitivity (or a preamp). Amateur-type RXs vary enormously in sensitivity at LF, a few are quite good, most are lousy, 20dB or more down on their HF performance. So this is a possibility, unless you have measured the sensitivity and know otherwise. Another possibility is that the input impedance of yours and Steve’s RXs are greatly different, producing different loading impedance on the loops.

The tuning adjustment should give you a very sharp peak – if not, either the impedance matching is drastically wrong, or something else in it’s construction is reducing the Q of the loop.

If I go the transformer route as you and several others have suggested,

do I need to physically remove the pickup loop or simply disconnect it?

The coupling loop should make little difference provided it is left open circuit.

Cheers, Jim Moritz

73 de M0BMU