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Message-ID: <5.1.0.14.0.20030901100341.00ad1620@gemini.herts.ac.uk>
Date: Mon, 01 Sep 2003 11:23:53 +0100
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
In-reply-to: <001901c36f1a$cef98e00$045bfea9@RSGB613192>
References: <5.1.0.14.0.20030829155231.02af4b10@gemini.herts.ac.uk> <5.1.0.14.0.20030830124931.02a8cdf0@gemini.herts.ac.uk> <002201c36efa$6e12a1a0$045bfea9@RSGB613192> <000401c36f09$ae1052c0$6507a8c0@Main>
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Subject: Re: LF: Re: GPS-locked PSK tests
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Dear LF Group,

As a "confidence check" of the GPS time/frequency standard stability, I 
monitored the phase of MSF relative to the standard's 10MHz output. MSF was 
received using an SPM-19 selective level meter, with the 10MHz standard 
driving the external reference input, and the 10kHz IF output of the SLM 
was compared on a 'scope with the 10MHz signal divided by 1000. This allows 
you to see a phase change of a few degrees. So far, over about 24 hours, 
there has been no overall phase change, indicating that the difference in 
frequency is no more than a few parts in 10^12. During daylight, there were 
practically no visible variations in phase, but at night, fluctuations of 
about +/- 10 degrees occurred over a period of several minutes, accompanied 
by the amplitude of the MSF signal varying over a range of about 3dB. My 
QTH is only about 100km from MSF, so I expect the ground wave signal 
largely swamps variations caused by changing sky-wave.

I think a DSP scheme like G4JNT is using is the best way of doing these 
phase measurements in the long run, but in the mean time, I intend to 
resurrect the "vectorscope" circuit I built a while back - this should also 
be able to remove the PSK modulation from the R4 and DLF carriers, with 
suitable choice of time constant.

Cheers, Jim Moritz
73 de M0BMU