You can find quite a bit of discussion about small loops if you search
the archives of this group. That, however, may confuse you because
some folk seem intent on making absolute statements about things they
don't really understand. Reputable books will tell you that the
"shield" is actually the antenna, and to gain the advantage of
rejection of local predominantly e-field noise, you must make the loop
very symmetrical. I know that Jasick's Antenna Engineering book has a
good chapter on loops, and King, Mimno and Wing's "Transmission Lines,
Antennas and Waveguides" has a good qualitative discussion of them.
There are various programs out there to help you determine the
performance of small receiving loops. I've found one on Reg Edwards'
web page to be useful.

Cheers,
Tom

John wrote:
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?

I found ON4UN's book lacking on this antenna.

Thanks in advance,
John, N9RF

Le 12 Aug 2006 14:59:50 -0700,
"K7ITM" a écrit :

You can find quite a bit of discussion about small loops if you search
the archives of this group. That, however, may confuse you because
some folk seem intent on making absolute statements about things they
don't really understand. Reputable books will tell you that the
"shield" is actually the antenna, and to gain the advantage of
rejection of local predominantly e-field noise, you must make the loop
very symmetrical. I know that Jasick's Antenna Engineering book has a
good chapter on loops, and King, Mimno and Wing's "Transmission Lines,
Antennas and Waveguides" has a good qualitative discussion of them.
There are various programs out there to help you determine the
performance of small receiving loops. I've found one on Reg Edwards'
web page to be useful.

Cheers,
Tom


The Balanis have an extended chapter on loops, but nothing on shielded
loop. But it is a very interesting reading in all cases, as well as
other books too.

John wrote:
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?


I think at it is because RG-59 is cheaper. The parasitic capacitance
don't have a big impact on a small loop because you will have to use an
additional capacitor to get the antenna to resonate on the frequency you
want to receive.

Cheers,
Dominique

I found ON4UN's book lacking on this antenna.

Thanks in advance,
John, N9RF