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Thanks Jim for the positive comments!
The SNR measured by opds was -58.3 dB on the
Opera average power scale, equivalent to -54.3 dB carrier power ("PEP") in
2.5 kHz. This would scale to -20.3 dB in 1 Hz or +21.7 dB in 64 µHz
(inverse of Op-4H sequence duration). Please note that the SNR measurement in
opds is not completely robust and could be pessimistic by a couple of dB.
The last figure 17.0 dB is for the SNR (peak-to-average power) of the
time-domain cross-correlation between the waveform and the callsign
template, stating the significance of the identification. In theory the
correlation result should be 6 dB below the PEP SNR, but it saturates at about
22 dB for strong signals.
Stefan also managed to detect my second run last
night:
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
The catch between Stefan and myself is that
for the ~ 180 km distance, on 9 kHz there is
normally a midday minimum due to skywave-groundwave cancellation, so the
lowest noise coincides with a low signal level. On the other hand, OK2BVG
at ~ 400 km gets both high signal and low noise at noon. Looking at Lubos'
grabber, the modulation sidebands are weakly visible in the "6000" window,
and it might even be possible to detect one another
using opds-32!
Anyhow I have now started a third Op-4H
sequence at 9:55 today, which should end around 14:16. Let's see what comes out...
Happy new year to all in the group,
73, Markus
Sent: Wednesday, January 01, 2014 10:58 AM
Subject: RE: VLF: 8970 Hz Op-4H
Congrats
Markus and Stefan!
Great
news, well done.
Am
I interpreting correctly in the following?
17dB
SNR with FFT bin width of ~ 69uHz, from ~~20uW ERP (9 meter antenna) at
175km?
I
will be celebrating VLF Opera tonight.
Happy
New Year,
Jim
AA5BW
Hi Markus, Stefan,
congrats to you, well done!
73 Joe
DK7FC JN49IK
VLF OPDS-4H correlation Range: 8969.87 ... 8970.23
Hz
date time
call distance frequency bandwidth snr
correlation
2013-12-31 18:07:58 DF6NM 175km
8970.000Hz 0mHz -58.3dBOp 100% 17.0dB
Wishing you
all a very good start into 2014!
Sent: Tuesday,
December 31, 2013 3:17 PM
Subject: VLF: 8970
Hz Op-4H
This morning
I have reconnected the VLF amplifier and coil to the antenna, and started
to transmit on 8970.000 Hz (Rb controlled). Sent a more or less
uninterrupted carrier between 12:30 and 13:30, and have started an Opera-4H
sequence at 13:41.
With 0.33
amps up to 9 m my estimated ERP would be around 20 uW. The carrier seems to
be well visible on the OK2BVG grabber (up to 10 dB in "600").
I'm now trying to reach opds-4H at DK7FC but the SNR (10 dB for
the carrier in "6000") may be just a bit marginal.
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