Found myself ordering a Trimble 10MHz GPSDO the other day.
I have a Thunderbolt but don't want to dedicate it to a
receiver because it's handy in the lab.

Andy wrote:
> The four-byte packet format has been selected so it is
> flexible enough to allow a timestamp to be included in
> the stream, and possibly some info on the block size,
> with blocks suitably labelled with a header for alignment

You might consider the packet format used by vlfrx-tools, which
(correct me if I'm wrong Wolf) can also be read by Spectrum Lab.
It has the fields you need and a magic number to sync on.

Rummaging through my junk box, there's enough parts for a
simple 137 kHz rx, one axis.  I've a spare BT878 card which
captures mono 8 bit samples at 448k/sec.  If I mix PPS and
a 137kHz pre-amp output, with a bit of luck that will give
coherent broadband reception at LF with absolute phase.

Then we can do some measurements to see how steady and
repeatable signal phase can be.  We might find that longer
paths are better.

Where's the natural noise floor at 137kHz? I guess it's around
10nV to 100nV per root Hz, depending on time of day, season?

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Paul Nicholson
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