[Fwd: LF: GPS locked tests]
andre.kesteloot at verizon.net
Sat Feb 4 14:54:10 CST 2006
-------- Original Message --------
Subject: LF: GPS locked tests
Date: Sat, 04 Feb 2006 19:03:37 +0000
From: Dave Pick <dave at picks.force9.co.uk>
Reply-To: rsgb_lf_group at blacksheep.org
To: <rsgb_lf_group at blacksheep.org>
I have just received this from Peter Martinez G3PLX who is conducting tests
with phase coherent GPS-locked signals on LF. He asked me to pass it on to
the group so that you'll know what's going on!
For info, CT1DRP is now radiating a plain carrier on 136718.75Hz, locked to
GPS. To give you an idea of what this means, if he triggered his scope from
the GPS 1Hz pulse, set a timebase span of 10uS or so, and looked at his
transmitter RF carrier waveform, it first shows a positive-going
zero-crossing, then 1 sec later a negative peak, then one sec later a
negative-going zero-crossing, and the a positive peak, and repeats that 4
sec sequence with no drift.
I am receiving in a similar fashion, and I am now able to measure the
received signal phase in absolute terms. It's early days but we hope soon to
be able to stay in phase over 24 hours. That means keeping the clocks with
which we generate RF at each end in time with each other to within a few uS
over a day. The signal itself, of course, drifts late in phase at night and
advances in the morning, typically by 2-3 cycles.
The significance of the frequency he is using is that it's a nice round
number that I can lock to (I work in whole Hz and simple fractions of a Hz)
and it's a nice round number that he can generate with his GPS-locked DDS
(His DDS steps in multiples of 5000000/(2^32) and 136718.75 is 5MHz*7/256.
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