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

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

Shielded loops are needed only when a small loop is used for
direction-finding purposes. It is then an angle-measuring instrument.

Shields serve no useful purpose on ordinary receiving and transmitting
loops. They reduce efficiency. All that is needed is a bare loop
conductor.

For multi-turn receiving loops download program RJELOOP3

For transmitting magloops download program MAGLOOP4 from website
below. Download in a few seconds and run immediately.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

"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

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

Try reading this John

http://www.w8ji.com/magnetic_receiving_loops.htm

73 Tom