Hello Jim, Stefan, and all,
Jim's screenshot definitely shows the 'Alpha' (RSDN) signal. It's
often difficult to tell which of the lines is the theoretic
'center' frequency - depending on how the various stations from
Russia arrive at your QTH, the carriers may be in-phase or out of
phase (i.e. cancel each other).
But you can alternatively check the sampling rate by fractions of
a Hz (or even a milli-Hertz) if NAA or NML is sufficiently strong
at your QTH. I have checked both here (as far as the signal
strength permits) against a GPSDO, and their center frequencies
seem to be very accurate (like most of the European navy
transmitters, too).
How to use these VLF MSK transmitters to 'calibrate' the
soundcard's sampling rate (in software) is described here:
http://www.qsl.net/dl4yhf/speclab/frqcalib.htm#MSK_signals
There should be two peaks in the spectrum shown in the
calibrator's scope window. These are located symmetrically around
the carrier frequency of the MSK signal, after the signal has been
squared. The difference between the two narrow peaks depends on
the transmitter's bitrate.
All the best,
Wolf .
Am 30.12.2013 17:20, schrieb hvanesce:
Stefan,
My stable/accurate time reference (GPSDO)
should arrive in two weeks; in the meantime I am hoping to use
11904.76190 Hz (per your
suggestion, thanks) to assess my soundcard clock frequency
offset. I have been guessing (based on comparison with
another uncalibrated but stable oscillator) that the
frequency offset of my soundcard gives less than 1Hz error
at 11904.76190 kHz.
I have attached a screenshot
captured over the last 24 hours, showing a modulated signal
centered at an indicated frequency (red marker) of
11905.1884 which would have a 0.426 Hz offset from
11904.76190 Hz.
The signal seems to be fading
about 40dB on a 24-hour cycle, with a minimum at ~ 2000 UT
(clock times in my screen capture are Arizona time, UT – 7
hours).
Could the modulated signal
shown here be the 11904.76190 Hz signal?
73, Jim AA5BW
