Topband: "Magnetic" receiving loop.

[Eric Scace K3NA]

Oddly enough, I am also building a portable loop antenna.  Yes, it performs worse than beverages or 
other receive antennas.  But a portable loop (~1.5m diameter) is very helpful for DFing RFI 
problems... and I have a fat S7 noise across 160m!

So far I have the loop itself done: two turns of RG-6 with the shields opened up at a point opposite 
from the feedline attachment.  It has deep (about 7 S-units) and very narrow (<10° in azimuth) nulls 
where it should.  But it's pretty deaf!  I can't hear the noise yet... only the very strongest signals.

Next steps are a resonating variable capacitor and a preamp.  Maybe I'll need a 3rd turn... but the 
books recommend keeping the overall length <0.1 wavelength.  I'd like to use this on other bands 
when chasing down RFI sources, so I put a switch in to choose the number of turns.

I've never done this before.  I'm just following the details in the current edition of "The ARRL 
Antenna Book".  Any hints will be appreciated from those with practical experience!

-- Eric K3NA