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LF: Re: Loop antenna problem W1TAG suggestion

To: [email protected]
Subject: LF: Re: Loop antenna problem W1TAG suggestion
From: "J. B. Weazle McCreath" <[email protected]>
Date: Sun, 22 May 2005 12:11:11 +0100
Delivery-date: Sun, 22 May 2005 13:07:37 +0100
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-- Original Message -----
From: "John Andrews" <[email protected]>
Sent: Saturday, May 21, 2005 10:45 PM
Subject: LF:Re: Loop antenna problem


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

Hello John, LFers,

Thanks for your suggestion on the series tuning setup.  Yesterday I tried a
simple non-shielded single turn pickup loop but it was no different than my
original shielded pickup.  I can't help but think that I'm getting led down
the garden path by something, but I'm amiss as to what!

Do you suppose that because I used #12 wire, rather than the #20 that
Steve, VE3SL, used on his loop that my Q is too high and therefore the
bandwidth is too narrow?  I think I'll wind a toroid transformer today
based on your info (I checked your website too) and see if I can get
better results.

Niels had suggested I try a capacitive divider, but my collection of caps
doesn't have anything close to the values he recommended.  I'll keep on
plugging away at it until I get it to work.





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