Dear Mike, LF Group,
I monitored the beacons around 137.77kHz last night using SDR-IQ receiver
and loop antenna - background noise was quite high due to a mains PSU
problem with the PC, but it was still possible to receive signals from the
US beacons reasonably well. As you can see from the screen shot, the
presence of G3XDV's beacon only about 10km and a few Hz away does not
greatly impair the reception of the US signals. The only significant effect
on the weaker signals is that the transients that occur at key on / key off
generate bright streaks with several Hz bandwidth overlapping the weaker
signals - these could be eliminated by increasing frequency seperation to 10
or 20Hz. Alternatively, slower rise and fall of the keying envelope would
reduce the bandwidth if these transients, at the expense of more
complication in the transmitter.
So operating local and DX beacons at the same end of the band does not seem
to be a massive obstacle to successful reception, and has the obvious
advantage that only one narrow-band receiver is needed to monitor all the
beacons, wherever you are. Perhaps it would be useful to organise some
sub-bands with 10 - 20Hz spacing between regions. Receiver performance may
also be an issue; the SDR-IQ has the advantage compared to "conventional"
receivers that the data used to generate the spectrogram effectively comes
directly from the front end of the receiver, without intervening IF, audio,
mixer stages, etc. The M0BMU QTH seems to be a good test-bed for this kind
of reception, due to closeness to G3XDV, so over the next few nights I
intend to try similar beacon reception with different RX set-ups.
Cheers, Jim Moritz
73 de M0BMU
----- Original Message -----
From: "Mike Dennison" <[email protected]>
To: <[email protected]>
Sent: Saturday, November 20, 2010 4:50 PM
Subject: LF: 136kHz Eu DX frequency - summary
...>
Is there a real problem? I don´t think there is a practical problem
at present. Activity is low and most stations are in touch with each
other via this reflector. If/when the USA gets an allocation at
136kHz, I can see a real need for some kind of plan, but that´s not
for a while yet.
...>
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