To: rsgb_lf_group@blacksheep.org
Date: Sat, 1 Feb 2003 08:46:43 -0500
Message-ID: <20030201.084648.-354351.0.n8tl@juno.com>
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From: n8tl@juno.com
Subject: Re: LF: RX loop designs
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Hello Jim:

I would appreciate the .pdf file for the loop commentary and designs as
mentioned 
in the attached mail.  I can be reached at   rlau@wcnet.org

Thankyou and best regards,

Tom N8TL

On Sat, 01 Feb 2003 11:32:31 +0000 James Moritz <j.r.moritz@herts.ac.uk>
writes:
> 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
> 
> 
> 
> 

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