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Date: Fri, 6 Aug 2010 13:48:55 +0100
Message-ID: <AANLkTi=kLM4zePYddSs48d_K8bTA9BNwsFM_4dCHqHH+@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Fwd: CMSK Beta released
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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 <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 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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<div>MSK does not lend itself to generation on a PIC.=A0=A0 It is NOT a tw=
o tone mode, but a waveform that transitions back and forth =A0around a ci=
rcle in phase space.=A0 Do not think of MSK as frequency Shift Keying</div=
>
<div>=A0</div>
<div>It may be possible to do it on a on a PIC.=A0 By not touching the fre=
quency register, but reprogramming the phase offset register in real time=
 at a fast-enough sampling rate.=A0 </div>
<div>=A0</div>
<div>But it would need a high sampling rate =A0to get it=A0right=A0while=
 keeping=A0alias sidebands at the sampling rate at a low enough level (sin=
(x) / x and all that)</div>
<div>=A0</div>
<div>PSK31 on a PIC, sampled at 7812.5Hz (250 samples per symbol) gives si=
debands at +/- N.Fs=A0of &lt; 60dBc.</div>
<div>=A0</div>
<div><br clear=3D"all">Andy<br><a href=3D"http://www.g4jnt.com">www.g4jnt.=
com</a><br><br><br></div>
<div class=3D"gmail_quote">On 6 August 2010 09:22, Michel F5WK <span dir=
=3D"ltr">&lt;<a href=3D"mailto:f5wk@mterrier.net">f5wk@mterrier.net</a>&gt=
;</span> wrote:<br>
<blockquote style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8e=
x; PADDING-LEFT: 1ex" class=3D"gmail_quote">Hi Graham, LF,<br><br>&gt; As=
 =A0far as I know , only wspr =A0and =A0ros-mf have =A0the =A0ability to=
 =A0drive =A0a<br>&gt; pic/dds =A0vfo , with =A0only =A0 =A0mf-1/7 =A0givi=
ng =A0a =A0tailored mf =A0qso =A0mode ?<br>
<br>What about asking for a mod allowing support of a DDS ?<br><br>MSK/CMS=
K has only two tones, whose frequencies are known. Therefore only one<br>b=
it of information is required for one symbol.<br>The big question is how=
 much accurate the deltaF has to be ...<br>
<br>Graham, since I swapped the link between the PC and the LF/MF transmit=
ter<br>from USB to BlueTooth, the timing has slightly degraded, and as a=
 result<br>ROSmodem is not working anymore. I have to resync the timing at=
 the PIC<br>
level, definitely the correct way ...<br><br>73,<br><font color=3D"#888888=
"><br>Michel - F5WK<br><br><br><br></font></blockquote></div><br>

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