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Most who are interested in VLF will be aware of the
excellent work of Paul Nicholson, who is running a very sensitive dual-loop
receiver for VLF and natural radio in Todmorden UK. He is also actively
interested in monitoring man-made VLF signals, and has provided outstanding
reception reports on several low-power transmit experiments.
With the recent upsurge of trying to put Opera mode
to work at VLF, Paul has kindly provided spectrum data during announced Opera-4H
transmissions from DJ8WX and myself. In Todmorden, signals from the two loops
are continuously being digitized along with GPS time stamps. The loops were
combined in software for maximum SNR from the expected direction, and noise
blanking was applied. Then relevant five-hour chunks were Fourier transformed
(0.12 Hz around 8970 Hz, 54.936 µHz bin width) and emailed to me. Here the files
were fed to unmodified Opds correlation software, using a search list containing
nine callsigns from potential VLF transmit stations http://dl.dropboxusercontent.com/u/26404526/callsloc_vlf.txt.
This process has resulted in four unambiguous hits:
Receiver: Paul Nicholson IO83XQ
Opds-4H 8969.94 - 8972.06 Hz
date time call
distance frequency bandwidth snr
correlation
2014-01-02 06:14:01 DJ8WX 760km
8969.997Hz 0mHz -54.1dBOp 100% 17.2dB
2014-01-02 01:50:49
DJ8WX 760km 8969.997Hz 0mHz -55.0dBOp
100% 18.0dB
2014-01-01 16:36:38 DJ8WX 760km
8969.990Hz 0mHz -53.6dBOp 100% 16.4dB
2014-01-01 14:22:32
DF6NM 1026km 8970.000Hz 0mHz -59.1dBOp 100%
16.3dB
For comparison, my first two Op-4H transmissions on
Dec 31st had been successfully detected by Stefan in Heidelberg, but have not
produced sufficient SNR in Todmorden at the time.
Receiver: DK7FC JN49IK VLF OPDS-4H
correlation Range: 8969.87 ... 8970.23 Hz
date time call
distance frequency bandwidth snr
correlation
2013-12-31 22:30:04 DF6NM 175km
8970.000Hz 0mHz -60.3dBOp 82% 14.2dB
2013-12-31 18:07:58
DF6NM 175km 8970.000Hz 0mHz -58.3dBOp
100% 17.0dB
Today we were able to also extract transmissions on
Uwe's new frequency 8270 Hz, although the SNR seemed not as good as
before:
Receiver: Paul Nicholson IO83XQ
Opds-4H 8269.94 - 8272.06 Hz
date time call
distance frequency bandwidth snr
correlation
2014-01-05 07:18:54 DJ8WX 760km
8270.000Hz 0mHz -57.2dBOp 97% 15.1dB
2014-01-05 02:55:38
DJ8WX 760km 8270.000Hz 0mHz -56.1dBOp
100% 14.4dB
2014-01-04 22:32:14 DJ8WX 760km
8270.000Hz 0mHz -57.6dBOp 100% 12.8dB
Best 73,
Markus
(DF6NM)
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