Larry:
There is no magic sense circuit design of which I am aware. My first DF
receiver used a DF96 1.5V filament valve as the sense amplifier. My next used a
germanium transistor which worked fine until I got too close to the hidden
station's antenna and all went quiet. I've updated a bit since then.
Most locally received signals have a significant vertical polarisation
component, and so the loop and sense whip can work well. The problem comes when
there is a predominant horizontal component because this can skew both sense
and bearing, as whilst a loop will respond to horizontally polarised signals it
has no directivity in that case. A small movement will generally allow better
results when one is fairly close to the target. In my experience, the real
problem arises when trying to DF skywave signals, and even more so where ground
wave and skywave are of similar strength.
There is a magic DF antenna, invented during WW1 by Frank Adcock. However, it
would be difficult (but perhaps not impossible) to make an 80m one small enough
to be carried around. Even better is the Wullenweber antenna, but that is
definitely not remotely portable.
A thousand DF hunts is quite a lot - once a week summer and winter for nearly
twenty years. I am not, and was not, saying that it is impossible to DF a
source to a particular building. I was saying, and am saying, that accidental
radiators usually couple into random conductors and that it is very easy indeed
to be misled.
73 Roger
VE3ZI
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