The Octo is working quite nicely with vlfrx-tools.
Getting less than a uS timing jitter on a good clean PPS.
The card actually delivers 8 input channels but chans 7 and
8 are silent.
To get the thing running, update your RPi firmware with
rpi-update
and then edit /boot/config.txt to add the line
dtoverlay=audioinjector-addons
and reboot. Then,
cat /proc/asound/cards
should report the interface is present as card 0.
A suitable vtcard command is
vtcard -d hw:0,0 -r96000 -b32 -c8 -L /run/vtcard.log -Bv @raw
-B puts it into background. I put the log file into ramdisk
/run, otherwise on my RPi at least, it produces card overruns
when vtcard occasionally blocks when writing its log file to
the SD.
Spectrum seems to be quite clean. The card runs reliably,
I've had no errors or overruns in 5 days of operation.
vtcard, vttime, and a single channel vtsid use about 25%
of a quad-core RPi capacity, so 3 cores are idle on average.
vttime should have six channels specified for input, ie
vttime -m ppsbase+,w=auto -c6 -L vttime.log -Bv @raw:1,2,3,4,5,6 @timed
where -c6 tells vttime that the PPS is on chan 6. If you try to
start it with all 8 channels, then vttime can't quite keep up
and it gives regular timing breaks as @raw overruns.
Measuring a 9765.625 Hz reference from a GPSDO through the Octo,
I'm seeing about a degree of phase jitter which isn't bad.
Plenty good enough for amateur radio coherent reception.
Monitoring for certain types of SID need a little better than that.
Conclusion: worked well but no longer available.
--
Paul Nicholson
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