Hi Remember that one model for FSK is a pair of AM signals that “just happen” to represent an FSK waveform. With normal FSK if you tune to one side, you will get a nice AM carrier and sidebands. With MSK it’s a bit more complex since they to do some cute stuff to cut down the bandwidth. It’s still got a pair of spikes in the spectrum at the upper and lower shift frequencies.
Probably the best way to get a timing signal is to recover the modulation and then “subtract” it from the original in software. That would be crazy with a high speed signal. With something like this - a pc plus sound card probably can do the job. More or less - “that must have been a 1 = do this to the history buffer, that must have been a zero = do that to the history buffer”. You would need to know a bit about how they filter their data stream for it to work well. The “proof” that you had it right would be a nice clean sine wave communing out of the history buffer. Spit it out the audio output port on the sound card and take a look ….. No I haven’t thought real hard about all the implications of doing that, there might be a gotcha in there somewhere. I’m assuming that they have a pretty predictable clock on their data. Beyond that I don’t think there are any other weird assumptions. I’d probably do the “de-fsk” by a phase modulation on the buffer. There might be a practical bump in the road there. Bob On Sep 14, 2014, at 10:20 AM, paul swed <[email protected]> wrote: > OK I am use to traditional fsk that typically had a far wide shift then the > baud. > What you say would match what the tracor book says and the system is > designed for. > I still do not see why if I offset the LO to -150 hz I get a useful display > to judge timing. I am using the lissajous method. > Regards > Paul > WB8TSL > > On Sat, Sep 13, 2014 at 11:25 PM, Jim Lux <[email protected]> wrote: > >> On 9/13/14, 7:13 PM, paul swed wrote: >> >> If NAA is transmitting 200 baud then I would expect the MSK carrier to be >>> +/- 100 Hz. Not +/-50 Hz. >>> >>> >> I'd expect the total shift to be half the baud rate: 100 Hz.. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
