Hi Jim,
This capture is taken from your home QTH, rigt? Or have you been out in
your car for 24 hours, just to minitor? ;-)
It looks nice and very clear with very low QRM, at least above 5 kHz.
The spectrum curve is surely a mixture out of the VLF noise floor, your
antennas frequency response and mains hum (just below 5 kHz). The MSKs
are relatively low in its level but not in its S/N, due to your band
limiting. You could easily lock your soundcard to GQZ at 22.1 kHz to
make an quasi atomic accuracy RX out of it (but the drifting carrier of
my 7th experiment was due to my upheating VFO and not due to your
soundcard drift, so its all no problem).
There is sometimes a trace arround 10,6 kHz which looks as a MSK signal
that cannot be there. I have observed the same line on my grabber. Do
you have an idea what can cause this trace on this QRG? But its all not
affecting the Dreamers Band! :-)
Since the signal (to noise) levels have been so strong in the last
experiment, i think i want to try DFCW-120 the next time, not only but a
part of the mesage. Seems to be no problem for you :-) I run F5WK's wav
file in QRSS-120 mode and it was no problem at all to see the signal...
I have inserted a switch to change the range of the antenna amperemeter
to 1A or 2A, so 6 dB more ERP is necessary to reach again the goal to
bring the needle to the catch ;-)
73, Stefan/DK7FC
Am 09.10.2010 09:53, schrieb James Moritz:
Dear Stefan, LF Group,
Thie attachment shows just over 24h of VLF spectrogram recorded using
the "wideband.usr" file you posted earlier. The period shown is
1200utc on 7/10 until 1200utc on 8/1, produced by editing 2 screen
shots together.
The noise level about 0 - 5kHz is predominantly mains harmonics, on
top of a continuum of noise that is due to impulses from an electric
fence somewhere nearby. Some of the noise is probably internal to the
PC. The baseline of the spectrum plot effectively shows the low
frequency response of the antenna/preamp.
The range 5 - 12kHz is dominated by mains-related noise during
daylight, with QRN rising during darkness. Actually, the mains noise
level was lower than usual during this period, compared to that during
last weekend's experiments.
The loop antenna orientation was the same E-W as used during reception
of DK7FC - this means several of the utilities are significantly
attenuated due to being away from the maximum directional response of
the loop.
Cheers, Jim Moritz
73 de M0BMU
1A_16kV.JPG
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