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<p>Andrew Talbot wrote:
<blockquote TYPE=CITE> <font size=-1>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 !</font> <font size=-1>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.</font> <font size=-1>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 )</font> <font size=-1>Andy G4JNT</font>
<blockquote
style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; PADDING-LEFT: 5px"><b><font face="Arial"><font size=-1>-----Original
Message-----</font></font></b>
<br><font face="Arial"><font size=-1><b>From: </b><a href="mailto:DL4YHF@aol.com">DL4YHF@aol.com</a>
<<a href="mailto:DL4YHF@aol.com">DL4YHF@aol.com</a>></font></font>
<br><font face="Arial"><font size=-1><b>To: </b><a href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a>
<<a href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a>></font></font>
<br><font face="Arial"><font size=-1><b>Date: </b>27 May 2001 22:29</font></font>
<br><font face="Arial"><font size=-1><b>Subject: </b>LF: Modulation pattern
on 16kHz ?</font></font>
<br> <font face="arial,helvetica"><font size=-1>Hi all,</font></font>
<p><font face="arial,helvetica"><font size=-1>During some RX experiments
in the VLF spectrum a few minutes ago, using a</font></font>
<br><font face="arial,helvetica"><font size=-1>bundle of ferrite rods and
lot of wire as antenna. There was..</font></font>
<br><font face="arial,helvetica"><font size=-1>- a quite strong signal
on 16kHz, 100 Hz wide;</font></font>
<br><font face="arial,helvetica"><font size=-1>- an other signal (stronger)
on 18.3kHz, more than 200 Hz wide;</font></font>
<br><font face="arial,helvetica"><font size=-1>- the Russian Navy(?) on
18.1kHz, about 100 Hz wide with a typical FSK</font></font>
<br><font face="arial,helvetica"><font size=-1>pattern (transmitter switched
off after the transmission).</font></font>
<p><font face="arial,helvetica"><font size=-1>An old list says on 16.0kHz
is "Rugby RTTY 75", another says its "RTTY 200".</font></font>
<br><font face="arial,helvetica"><font size=-1>But the signal on 16kHz
looks more like a well-shaped PSK signal to me. Or is</font></font>
<br><font face="arial,helvetica"><font size=-1>it just a very stable QRM
in my neighbourhood..</font></font>
<p><font face="arial,helvetica"><font size=-1>Any information available
on this reflector ? If the signal on 16.0kHz is</font></font>
<br><font face="arial,helvetica"><font size=-1>really PSK, where will the
planned CW transmission be on Tuesday afternoon ?</font></font>
<p><font face="arial,helvetica"><font size=-1>Thanks in advance for any
info,</font></font>
<br><font face="arial,helvetica"><font size=-1> 73's from Wolf DL4YHF.</font></font></blockquote>
</blockquote>
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