Dear Mal, LF Group,
G3KEV wrote:
...>Information is also scarce in the UK especially about receiving
capabilities, what is being heard especially alpha signals, strength,
audibility and general band noise.
If you read previous posts to this reflector on the subject, you will know
that the receive side of things is fairly straightforward. What is being
heard on 9kHz is QRN and QRM, except for very short range "induction" tests,
where the signals can be audible. If you cannot receive the "Alpha" beacons
in the UK, it probably means they are not transmitting, or your RX or
antenna have stopped working. But, although they may be interesting in
themselves, they are largely irrelevant as a measure of 9kHz receive
performance, since they are on a different frequency, are vastly more
powerful than amateur signals, and for the DX tests that have been done,
have a much wider bandwidth / shorter duration compared to the amateur
signals.
A better test of receiver performance at 9kHz is to compare the noise level
with and without the antenna. Since the RX or preamp noise level can be
strongly dependent on the source impedance, it is best to replace the actual
antenna with a "dummy antenna" with similar impedance when making this
comparison. For example, for my loop antenna, I have a change-over switch
that connects the preamp input to a small choke with about the same
inductance and resistance as the actual antenna. This enables quick
comparisons to be made between noise levels at different times and
locations, and is also a good check on the local QRM level. Obviously, you
want the antenna noise level to be at least several dB greater than that
with the dummy antenna, which is usually easily achieved.
The general band signal and noise levels are being regularly monitored at
several locations - you can see the info at http://abelian.org/. But you
already know that...
Cheers, Jim Moritz
73 de M0BMU
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