Hello Gerhard, Ossi, and group,
This info just arrived here from the yahoo VLF group, not sure if it was
already forwarded to the LF group. 73, Wolf DL4YHF .
VLF transmit activity from Austria
Date: Mon Jan 24, 2011 5:48 pm ((PST))
OE3GHB's signal is a moving target! The frequency drifts
quite a lot but yesterday (24th) for a couple of hours the
drift was fairly linear and I could apply a suitable de-chirp.
Integrating 12:00 to 14:00 in 138uHz resolution with a chirp
rate of -1.05uHz/sec produces a peak of about 0.18fT crossing
8969.9676 Hz at 12:00,
It's a pretty marginal sort of peak, but the frequency coincides
with Gerhard's local spectrogram at 12:00 and is not present
before the transmission.
The required de-chirp was first estimated by counting pixels
on Gerhard's spectrogram, then polished by running several
spectra with a range of nearby values. Actually the chirp
rate giving the highest peak was the original rate estimated.
Without the de-chirp, his signal is spread across some
50 spectrum bins and is almost completely lost in the noise.
There's a spurious signal here at 8969.95683 Hz, visible without
Gerhard's signal is just visible as the broad hump between -0.03
and -0.04Hz. The bin amplitudes there are not individually
significant against the prevailing noise, but 36 adjacent raised
bins does indicate the presence of something and if the excess
power was concentrated into a single bin the amplitude would
be between 0.3 and 0.6fT. I guess the drift rate is just not
linear enough to fully concentrate the signal.
The range to JN88hl is 1422.5 km, so a little further than
Ossi. I think Gerhard must be putting out quite a nice
signal but it is lost because of the frequency drift.