Wolf,
Thank you for the information. I opened the link that you provided and read most of the document; this is a big help. I am in the early stages of familiarizing with the Spectrum Lab manual, and did not realize that Spectrum Lab had such user-friendly synchronization options; they are most impressive. I will experiment with synchronizing to NPM, NAA and NML (those three signals are often within 5dB of one another here). The sample rate and frequency calibration document to which you provided a link will be a big help.
I am also waiting for delivery of a Thunderbolt GPSDO, and I noticed and reviewed the very thorough description of 1pps GPSDO interfacing and configuration, in your sample rate and frequency calibration document. Sincere thanks to you for all of this great software and the excellent documentation, it is all much appreciated.
73, Jim AA5BW
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
