Another magnetic loop

[Brian Hawes]

Hmm ...

I'm very interested in electrically small loops, having minimal real estate here at home. 
I do have issues with the coupling on some of these designs.

The idea of a Faraday Shield around the coupling loop is fine. and that has to be electrically incomplete to work as an electrostatic shield and
not a shorted turn. Putting the break in the centre of the shield may or may not be better.
But -  several of the designs on the  internet, and this one too, if I read the drawings correctly, have the inner and outer connected 
at that central break in the shield.
I don't understand that. Is it correct, or just an error in somebody's design which has been perpetuated on the net?

I have run a F.E. simulation of a loop of similar dimensions and get a coupling factor k of about 0.05. Quite light. 

There are other coupling methods out there: Ferrite transformers for QRP designs. G4FON has a design which uses a 0.5-inch toroid
for 10-Watts, G4TPH uses two 1.5" toroids stacked, for 40-W. Both on 14 MHz BTW. 
I can't see why a small Ferrite transformer shouldn't handle much higher power with the right material. Amidon/Fair-Rite type 67 does it for me.

How one calculates the coupling with a 1-Metre loop passed through a small toroid, I don't know. I would like to. For me, something is
not real until I can run it as a SPICE simulation!

That copper trombone looks nice, but for my money a used Vacuum Variables isn't too expensive against the effort it saves. You just have
to haggle at Hamvention.

See some of you there!

Brian

________________________________________
From: tacos-bounces+hawes=herald.ox.ac.uk at amrad.org [tacos-bounces+hawes=herald.ox.ac.uk at amrad.org] On Behalf Of Andre Kesteloot [andre.kesteloot at verizon.net]
Sent: 07 May 2011 15:08
To: Tacos
Subject: Another magnetic loop

http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf

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