Envelope-to: dave@picks.force9.co.uk
Delivery-date: Sat, 21 May 2005 23:46:56 +0100
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From: "John Andrews" <w1tag@w1tag.com>
To: rsgb_lf_group@blacksheep.org
References: <000c01c55a6e$8d82f740$37d0fc3e@l8p8y6> <000d01c55b45$acb45e60$ac068351@w4o8m9> <002f01c55d97$09df4840$8c802ed8@server> <000901c55d99$bb7d7cf0$0700a8c0@Laptop> <005201c55e00$e1f57ce0$8c802ed8@server>
Date: Sat, 21 May 2005 22:45:36 +0100
MIME-Version: 1.0
Subject: LF: Re: Re: Re: Loop antenna problem
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J.B.,

There is another approach you might want to consider. Skip the single turn
link altogether. Rather than the normal parallel tuning, series tune the
loop into a transformer wound on a ferrite core. The turns ratio of the
transformer will determine the Q of the loop. You might not want a really
high Q setup with a loop of that size.

I have been using a 10 turn (on the loop side) to 20 turn transformer to
couple to a 50 ohm termination. This places a nominal 12.5 Ohms in series
with the loop. A higher ratio would improve the Q, but this might be a good
starting point for you to play with. The core material in this case is #77,
but #43 or similar should be OK.

The advantage of this arrangement is that the loop remains inherently
balanced to ground, while giving you the flexibility of playing with the
coupling. You may choose to put the preamp right at the transformer
secondary, or run a coax line back to the shack. A short write-up on my
arrangement is available at:
http://www.w1tag.com/rxloop.htm

John Andrews