----- Original Message -----
From: "J. B. Weazle McCreath" <[email protected]>
To: <[email protected]>
Sent: Sunday, May 22, 2005 12:11 PM
Subject: LF: Re: Loop antenna problem W1TAG suggestion
-- 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.
This is probably the best approach for your loop, or any series or parallel
arrangment
I use a parallel resonating approach on my 80 m perimeter vertical loop and
never had a problem.
G3KEV
| 