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Message-ID: <5.1.0.14.0.20021126174220.00b19580@gemini.herts.ac.uk>
Date: Tue, 26 Nov 2002 18:22:35 +0000
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
In-reply-to: <5.1.0.14.0.20021125171906.00b9d028@pb623250.kuleuven.be>
References: <001d01c29475$f77f6140$0500a8c0@charter.net> <3DE1338E.2F1E9274@att.net> <000801c29474$a4e23300$1ee086d4@erica>
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Subject: Re: LF: loop antenna
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Dear Rik, LF Group,

I reckon your loop will have inductance of the order of 100uH, so with the 
kind of currents you are hoping to achieve, the voltage on the loop will 
reach at least a few kV. With this voltage, I believe you will need 
insulators between the wire and the tree branches to prevent them getting 
burnt away where they contact each other. Also, if you use a transformer to 
"float" the loop, this could have similar  voltages between the windings.

It is not easy to make a transformer with a large impedance ratio and at 
the same time low loss and low leakage inductance. I would suggest 
something like the output transformers used in HF solid state PAs, with a 
single turn low Z winding of tubing or strip passed through a number of 
stacked ferrite cores to get sufficient winding inductance. As an 
alternative to vacuum capacitors for tuning, you could use a variometer of 
a few uH in series with the loop - it would only need a few metres of wire, 
and if you used the same litz wire as for the antenna, it would make 
negligible difference to the loss.

BTW - if you get the loss down to 0.2ohm, the Q will be over 400  - so you 
will certainly need accurate tuning!

Cheers, Jim Moritz
73 de M0BMU