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Jim, thanks for this
interesting plot. As the trace is still on my screen here, I decided to follow
your footsteps, and generated the attached plot. It shows Ossi's
frequency offset (mHz from 8970 Hz, blue), signal level (arbitrary dB
units, red), and approximate noise (dB in 1.5 x 0.95 mHz, green). The ascii
data are also attached.
As Mal and Rik say, we would expect some ERP
variation from a balloon antenna, equally affecting all receiver sites.
Ossi does run a local grabber about 10 km from his transmitter (screenshot
attached). Unfortunately the spectrogram colourscale does
not differentiate minor ERP variations. The outage at 11:20 had
been reported yesterday.
The interesting large variations in Jim's plot
(about 6 dB pp) do not seem to appear here. This would hint towards a
propagation effect, which seems odd as the timescale (half hour period)
is a bit too fast for ionospheric Doppler at that range. As the signal
at M0BMU was apparently not too far above the noise, some fluctuations
might have been contributed simply by the stochastic noise vector
addition.
Today Ossi is transmitting again. He is about
10 dB weaker than yesterday so probably running "barefoot" without the
balloon.
Best 73,
Markus (DF6NM)
Sent: Tuesday, February 08, 2011 12:09 AM
Subject: LF: Re: OE5ODL over different paths
Dear Ossi, Markus, LF Group,
I was quite interested to
notice the sharp dip in OE5ODL's signal at around
1430utc today, and in
light of Markus' comments, I used the cursor
facilities in SpecLab to
manually read off the signal levels, avoiding the
noise bursts. I also did a
quick field strength calibration of the
loop/receiver - the resulting plot
of field strength vs time is shown in the
attachment (the vertical axis
should say "dBuV/m"). As well as the deep null
around 1430, the signal level
seems to rise several dB during the day,
peaking around 1800 - 2000, and now
starting to fall off. Also, a downwards
drift in frequency of about 1.5mHz
can be seen.
Cheers, Jim Moritz
73 de M0BMU
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