Dear LF Group,
I monitored VLF frequencies between 5 and 15kHz last night in an attempt to
detect signals from the IMAGE satellite, but nothing was heard or seen that
could have been it. The Alpha beacons were back on, (operators found some
coins for the meter?) and clearly audible.
However, this morning I had the computer on for other purposes at around
1000 this morning, and thought I would check to see if there was any
difference between night and daytime reception on these frequencies. I was
using Spectrum Lab's "software receiver" facility to convert the Alpha
beacon just below 15kHz down to audio, when I heard a strong carrier tuning
up on the frequency, followed by some minutes of tests and transmissions in
some digital mode. I thought this might be an intermod or alias from higher
frequencies at first, but was able to receive the same signal on my RA1792
with tuned loop - this revealed that the signal was actually on 13.3kHz,
the "audio image" response of the Spectrum lab receiver as I had it
configured. A small piece of the spectrogram is attached, showing the
carrier and a burst of the modulation. The bandwidth shown is about 280Hz,
and the separation between spectral lines is about 25Hz. The weaker trace
is the alpha beacon. I have not seen a data transmission this low in
frequency before, and the strength was not far short of that from GBR, so
must have been fairly local. The modulation looks a little like what CFH
was testing at one time last winter. Any ideas?
Cheers, Jim Moritz
73 de M0BMU 
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