[Lf] FSK on 16kHz ?

[Andre' Kesteloot]

Andrew Talbot wrote:

>  The 16kHz transmission is MSK  (Minimum Shift keying).   An
> efficient, constant amplitude, data modulation format.   There was
> quite a bit of discussion about the mode on this reflector a few
> months ago, and I remember stating that the 16kHz transmission was one
> of the most "perfect" examples of MSK I have ever seen off air ! The
> 'minimum' of MSK refers to the fact that the frequency shift is the
> absolute lowest that can be used for FSK modulation, being exactly
> half of the data rate.   MSK is a mode that must to be received
> coherently, like PSK, to take any advantage of its good signalling
> properties.   The constant amplitude nature would make MSK the ideal
> mode for our use on 137k were it not for the difficulty of
> demodulating properly.   I believe Bill de Carle, VE2IQ has been
> working on an MSK implementation for some time now, but a good system
> for the mode is still some way off. Low cost and inefficient,
> non-coherent, implementations are widely used at higher frequencies -
> a quick scan across the VHF spectrum reveals many MSK transmissions
> carrying telemetry, data, paging, and all sorts of signals.  A crude
> demodulation can be done simply using a PLL as an FM discriminator,
> but that gives a result no different from narrow shift FSK.    An off
> the shelf chipset, the CM589, makes for a low cost simple MSK data
> modem, but the implementation is geared towards high S/N paths and the
> chip will not suit our weak signal purposes.  (I've already looked at
> it ) Andy  G4JNT
>
>      -----Original Message-----
>      From: DL4YHF at aol.com <DL4YHF at aol.com>
>      To: rsgb_lf_group at blacksheep.org
>      <rsgb_lf_group at blacksheep.org>
>      Date: 27 May 2001 22:29
>      Subject: LF: Modulation pattern on 16kHz ?
>       Hi all,
>
>      During some RX experiments in the VLF spectrum a few minutes
>      ago, using a
>      bundle of ferrite rods and lot of wire as antenna. There
>      was..
>      - a quite strong signal on 16kHz, 100 Hz wide;
>      - an other signal (stronger) on 18.3kHz, more than 200 Hz
>      wide;
>      - the Russian Navy(?) on 18.1kHz, about 100 Hz wide with a
>      typical FSK
>      pattern (transmitter switched off after the transmission).
>
>      An old list says on 16.0kHz is "Rugby RTTY 75", another says
>      its "RTTY 200".
>      But the signal on 16kHz looks more like a well-shaped PSK
>      signal to me. Or is
>      it just a very stable QRM in my neighbourhood..
>
>      Any information available on this reflector ? If the signal
>      on 16.0kHz is
>      really PSK, where will the planned CW transmission be on
>      Tuesday afternoon ?
>
>      Thanks in advance for any info,
>       73's from Wolf DL4YHF.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://atanasoff.rf.org/pipermail/lf/attachments/20010528/225da1c3/attachment.html