"John" wrote in news:1155400389.854352.27800
@p79g2000cwp.googlegroups.com:

Hello all,

I am new to the group and have a question.

Does anyone know a good source of information on small (less than
.1wl), shielded (coax) magnetic loops? In particular, I would like to
know design equations (are ON4UN's formulae correct and complete?). Why
do most people use RG-59 rather than a thicker coax (shielding, C/ft?)?
Why is 20' for 160 meters the norm? Discarding mechanical
considerations, wouldn't thicker coax provide greater efficiency?

In a receiving antenna, efficiency is not as important as in a
transmitting antenna, especially on 160 and 80m where the noise floor is
usually far louder than the receiver's front end. A little antenna
attenuation may actually HELP with intermod distortion and other receiver
problems.

I've made working loops for both bands from LMR400 that can actually be
hung out and used for transmitting. They are about 4 feet in diameter
and performance is so-so, but they work. I used the internal capacitance
of the coax to resonate them (a lot of cut and test with the analyzer)
and matched them with a large gimmick capacitor of flat phone wire wound
onto the loop near the feedpoint.

Look up Ted Hart's small loop design. Mine are similar, only I did two
turns for the 160 loop (it's actually physically smaller than the 80m
loop by a bit).


--
Dave Oldridge+
ICQ 1800667