Date: Sat, 01 Feb 2003 07:49:48 -0500
From: "Ralph Lane" <rlane7301@comcast.net>
To: rsgb_lf_group@blacksheep.org
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Subject: LF: Re: RX loop designs
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Jim, sounds like interesting designs. I would like a copy.
Thanks,
Ralph

----- Original Message -----
From: "James Moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Saturday, February 01, 2003 6:32 AM
Subject: LF: RX loop designs


> Dear LF Group,
>
> With the recent chatter about LF loops, I finally got round to writing up
3
> of my receiving loop designs, which I have been using for the last year or
> so. They seem to be significantly different to the designs other people
> have come up with, and work well, so could be of interest.
>
> The usual problem with a tuned loop is that the bandwidth is very narrow,
> so remote tuning is needed. Resistively loading the loop increases BW, but
> reduces the loop output and SNR, so a bigger loop is needed, and also
> out-of-band selectivity is reduced. My idea was to add an additional tuned
> circuit coupled to the loop to produce a bandpass response, which can be
> designed to give a flat-topped or slightly double-peaked response covering
> the whole 136kHz band without re-tuning. This has turned out to work well,
> and the article describes one 1m^2 loop with a bandwidth of about 4kHz,
and
> a 2m x 2m loop using a single turn of tubing with a bandwidth of about
> 18kHz. With the simple pre-amp also described, the noise floor of both
> these antennas is well below the band noise even on a quiet day.
>
> The article also includes a wideband loop based on a low-pass rather than
> bandpass design, which covers 10kHz -200kHz, also a single turn 2m x 2m
> loop. This is slightly less sensitive than the bandpass designs, but more
> than adequate for general use over the LF/VLF range. The relationship
> between field strength and loop output for this antenna is predictable, so
> it can also be used for field strength measurement.
>
> The article I have written is 5 pages, with several diagrams, and is a
.pdf
> file of about 340kB. It is too big for the reflector, but if you are
> interested, let me know, and I will e-mail it to you as an attachment.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>