Andy,
I found on the web a few interesting pages of the book: "Research on the DDS
to Generate MSK Signal"
<
http://books.google.fr/books?id=ITOlbhvbAbQC&pg=PA36&lpg=PA36&dq=MSK+DDS&source=bl&ots=wcQBVR20gz&sig=ETkZuXXeYofIAxL7HvqtrVULclU&hl=fr&ei=mg9cTPe-I5K94ga-hdicAg&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCgQ6AEwAg#v=onepage&q=MSK%20DDS&f=false
>
Michel - F5WK
> MSK does not lend itself to generation on a PIC. It is NOT a two tone
> mode, but a waveform that transitions back and forth around a circle in
> phase space. Do not think of MSK as frequency Shift Keying
>
> It may be possible to do it on a on a PIC. By not touching the frequency
> register, but reprogramming the phase offset register in real time at a
> fast-enough sampling rate.
>
> But it would need a high sampling rate to get it right while keeping
> alias sidebands at the sampling rate at a low enough level (sin(x) / x and
> all that)
>
> PSK31 on a PIC, sampled at 7812.5Hz (250 samples per symbol) gives sidebands
> at +/- N.Fs of < 60dBc.
>
> Andy
> www.g4jnt.com
> On 6 August 2010 09:22, Michel F5WK <[email protected]> wrote:
> Hi Graham, LF,
>> As far as I know , only wspr and ros-mf have the ability to drive a
>> pic/dds vfo , with only mf-1/7 giving a tailored mf qso mode ?
> What about asking for a mod allowing support of a DDS ?
> MSK/CMSK has only two tones, whose frequencies are known. Therefore only one
> bit of information is required for one symbol.
> The big question is how much accurate the deltaF has to be ...
> Graham, since I swapped the link between the PC and the LF/MF transmitter
> from USB to BlueTooth, the timing has slightly degraded, and as a result
> ROSmodem is not working anymore. I have to resync the timing at the PIC
> level, definitely the correct way ...
> 73,
> Michel - F5WK
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