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Dear LF group,
recently I found that the excellent 7-band web
receiver at Twente University http://websdr.ewi.utwente.nl:8901/ also features a low frequency section (64
to 164 kHz). In contrast to the situation a few months ago, the LF band now
appears to be completely cleared of local interference, and the
receiver is quite sensitive.
By connecting the PC's audio output to
the line input by a "real" physical audio cable, I was able to perfectly
read 137 kHz QRSS3 signals on a slow spectrogram. The audio resampling
process from nominal 8438 Hz samplerate does
introduce up to +- 0.2% of samplerate variation, but the resulting frequency
instability can be mitigated by tuning to a low beat frequency (eg. about
300 Hz). The digital IF bandpass skirts can be pulled in as required. Using WSPR
v2 with an appropriate Rx-BFO setting, it was possible to successfully
decode WSPR signals that way as well.
The web-SDR waterfall also shows a strong
Loran-C spectrum around 100 kHz (mostly from Sylt, 300 km from Enschede).
This tempted me to feed its output to my "LoranView" averaging
program. With samplerate tracking to the Sylt pulses and
five minute averaging, I could detect traces from 48 different Loran
stations last night, including far away ones like Port Clarence (Alaska),
Raymondville (Texas) and Gesashi (Japan, 9582 km).
Many thanks to Pieter-Tjerk PA3FWM, for providing
us with this outstanding peace of work!
73,
Markus (DF6NM)
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