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Message-ID: <7D653C9C42F5D411A27C00508BF8803DCB99B8@pdw-mail-r1.dstl.gov.uk>
From: "Talbot Andrew" <ACTALBOT@dstl.gov.uk>
To: "LF Group \(E-mail\)" <rsgb_lf_group@blacksheep.org>, 
 "PLX \(E-mail\)" <Peter.Martinez@btinternet.com>
Subject: LF: GPS Locked PSK
Date: Tue, 12 Feb 2002 12:46:19 -0000
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I am now in a position to transmit GPS locked and timed PSK signals using
the high power transmitter giving around 100mW ERP - at least it should be
that power when the weather eventually stops raining.  A  lower power Tx is
also available for microwatt ERP levels.  
Software driving the DDS module can generate any of these types of PSK data
:

	Pure binary code, specified as Hex or by its 1/0 sequence.
	ASCII - non differentially coded in the Varicode alphabet as used
for PSK31.
	As above, but differentially coded to remove the phase ambiguity but
giving 2* error rate.
	CW representation,  where key down = 0 deg, key up = 180 deg
	    - Ideal for visual decoding on a time / phase plot but less
efficient than varicode.

Data rate can have any bit period that is an exact multiple of one second,
and timed to UTC pulses.  For decoding purposes it may be convenient to
define a time reference, such as the hour, where the data sequence starts;
and also to define the start polarity at that point.

Frequency using the GPS locked reference can be any exact multiple of 1/1024
Hz (so all 1Hz values are possible)  but could have up to 20 degrees of
phase jitter on it over a period of a few seconds.  The effect of this is to
give 1Hz sidebands at a level of -40dB.    A more short term stable source
can generate Caesium, MSF or TV sync locked frequencies that are based on
6.5536 MHz / 2^32, so exact Hz multiples are available every 25Hz.  I prefer
not to have the Cs tube runing for extended periods as it has got to last a
lifetime and I don't know how many hours are left in the tube.

So if anyone is ready with vectorscopes, PSK demodulators etc.........

Andy  G4JNT


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