Dear Stefan, LF Group,
This capture is taken from your home QTH, rigt?
Yes, this is the same QTH and equipment as used for your lests last week,
although without the 9kHz bandpass filter connected.
It looks nice and very clear with very low QRM, at least above 5 kHz.
Usually there are more spectral lines due to mains-borne QRM. But the low
local noise level gives a better picture of the QRN.
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.
The antenna/preamp response is flat between about 3kHz - 22kHz, and the
shape of the noise floor spectrum looks quite similar to that displayed on
Paul Nicholson's web pages, so I think the plot reflects the actual noise
level reasonably accurately. The loop is oriented E-W, while several of the
utilities are approximately N-S from this QTH, so these would be stronger
if an omni-directional antenna were used
You could easily lock your soundcard to GQZ at 22.1 kHz to
make an quasi atomic accuracy RX out of it
For the type of tests done so far, the long-term drift that occurs does not
matter much, but the short-term fluctuations that I experienced in the sound
card with a period of ~1 - 2minutes probably do significantly reduce the
SNR. I have not yet tried the SpecLab locking facility yet - definitely
something for the next test!
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?
I had not seen this before here - will have to have a look.
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...
Should be no problem here...
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 ;-)
...But keep watching out for smoke and flames ;-)
Cheers, Jim Moritz
73 de M0BMU
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