Dear LF group,
I too can hear this - it has always been there since I started on LF,
and does sound like very weak CW, but is never readable. I can
hear it at any time the noise level is fairly low, and it is normally
always visible on spectrogram displays.
I had a look at it last night using Spectrum Lab and Argo at their
higher resolutions, and it is not actually CW at all - it consists of a
dozen or so carriers irregularly distributed between about 135.998
and 136.001kHz. Some of these are rock steady, others were
drifting up or down by a fraction of a hertz over the two hours I
observed them. The different frequencies beating together gives
the "CW" effect
The spread in frequencies and the amount of drift would be
consistent with an assortment of crystal oscillators on the same
nominal frequency - perhaps it is a harmonic of some popular baud
rate or similar?
Cheers, Jim Moritz
73 de M0BMU
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