Hello Stefan,
Yes, the charm of the GPS-sync'd sampling is that it allows truly
coherent transmission - even after the program was shortly stopped, PC
rebooted, generator re-fuelled, or whatever strange things may happen.
The sine wave generator will (optionally) not calculate the argument
based on the number of soundcard samples, but derived from the
GPS-derived time of day. Which, with the GPS 18x LVC mentioned before,
seems to have a resolution (not neccessarily a precision) in the
sub-microsecond range (192 kHz SR -> 5.x microsecond samples, but
internally interpolated to a higher sample rate near the slope of the
sync pulse).
At 192 kHz sampling rate, I get a standard deviation in the measured
pulse position of only 30 to 60 nanoseconds (per one-second-interval)
measured over one minute, which almost sounds too good to be true. Thus
i'm a bit sceptic, this needs more testing.
Some preliminary info about the GPS-based calibration is already
available here:
http://www.qsl.net/dl4yhf/speclab/frqcalib.htm#gps_pps_output
Note: The NMEA decoder for the soundcard is not implemented in the SL
version on my website. It will be implemented when the weather(!)
permits ;-)
73, Wolf DL4YHF
(off for a walk now..)
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