Date: Fri, 6 Aug 2010 16:13:49 +0200
From: Michel F5WK <f5wk@mterrier.net>
Message-ID: <561509842.20100806161349@mterrier.net>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Fwd: CMSK Beta released
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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=3DITOlbhvbAbQC&pg=3DPA36&lpg=3DPA36&dq=3DM=
SK+DDS&source=3Dbl&ots=3DwcQBVR20gz&sig=3DETkZuXXeYofIAxL7HvqtrVULclU&hl=
=3Dfr&ei=3Dmg9cTPe-I5K94ga-hdicAg&sa=3DX&oi=3Dbook_result&ct=3Dresult&resn=
um=3D3&ved=3D0CCgQ6AEwAg#v=3Donepage&q=3DMSK%20DDS&f=3Dfalse
>

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
> =20
> It may be possible to do it on a on a PIC.  By not touching the frequenc=
y
> register, but reprogramming the phase offset register in real time at a=
 fast-enough sampling rate.
> =20
> 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)
> =20
> PSK31 on a PIC, sampled at 7812.5Hz (250 samples per symbol) gives sideb=
ands at +/- N.Fs of < 60dBc.
> =20

> Andy
> www.g4jnt.com


> On 6 August 2010 09:22, Michel F5WK <f5wk@mterrier.net> 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 transmitte=
r
> 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