Spent some time today cobbling together a receiver for
137 kHz.   System noise measures about 4nV/m equivalent
field strength in 1Hz with a BF245B front end but I've
not yet attached it to an antenna - that's usually when
the trouble starts.

The mono audio input of the BT878 video card timestamps
fairly well while sampling at 448k samples/second.  It's
a bit noisy: 3.5 uV RMS in 1Hz at the line input, which
means I needed to build in quite a bit of rx gain to
overcome the card floor.

Because it's a mono audio input I have to mix the GPS PPS
and the LF, then separate them again in software.

Hopefully soon then, some phase measurements at LF.

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Paul Nicholson
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