Message-ID: <01C37091.4B597AB0.g4jnt@thersgb.net>
From: "Andy talbot" <g4jnt@thersgb.net>
To: rsgb_lf_group@blacksheep.org
Date: Mon, 1 Sep 2003 13:59:08 +0100
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Subject: RE: LF: Re: GPS-locked PSK tests
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At the moment that is basically all that I'm using.  An analogue vectorscope 
made by multiplying two quadrature  1kHz waveforms by the output fom the Rx 
after passing though a 1kHz bandpass filter.  The outputs from each multiplier 
are then passed through a pair of identical 10Hz low pass filters. Everything 
up to this point is done with op amps and simple CMOS.  At this stage the 
outputs could be viewed on a 'scope in X-Y mode, but I choose to digitise them 
and process with further integration on a PC.  This allows the exact phase to 
be calculated rather than estimated from a scope trace.

There is nothing to stop the low pass filters being made much narrower and 
sticking with a simple scope to view the signal.  I can send a copy of the 
circuit of the analogue part of the electronics to anyone interested.  It also 
includes a simple LED based phase display driven from the 1kHz bandpass filter 
output, so a strongish signal can be seen to rotate around a circle of 8 LEDS.

The next stage is to do the 1kHz quadrature multiplication and avergaing in a 
PIC, but as the system works Ok as it is, that is a low priority job.

Andy  G4JNT

.

>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.
>s