Dear LF Group,
I have been doing some work recently on a preselector/convertor design for
LF - The idea is an easy-to-build project to get started on LF that does
not require test gear, alignment, or coil winding. I have a breadboarded
circuit working quite nicely at the moment - the preselector has a tuned
input circuit which can be adapted to a wide range of antennas without
requiring a specially made antenna loading coil. A RX that covers LF can
use the preselector output directly, or an oscillator/mixer circuit can be
used to mix the signal up to HF. Although the up-convertor is fine for many
applications, for the narrow band modes it is obviously better if you can
use the circuit as a preselector with the main receiver tuned to LF,
because this reduces drift.
The problem is to know what gain is required from the preselector. I know
several people have measured the sensitivity of their receivers, which
varies a lot at LF - so I would be very grateful for any figures anyone has
to hand for typical amateur receivers, so that I can design in gain levels
that will suit the majority of peoples' equipment.
Cheers, Jim Moritz
73 de M0BMU
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