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 [email protected]
Thankyou and best regards,
Tom N8TL
On Sat, 01 Feb 2003 11:32:31 +0000 James Moritz <[email protected]>
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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