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
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