Larry Kayser wrote:

Brooks Shera published an excellent article in QST on "disciplining" a
frequency standard to the GPS 1 PPS signal.

I have built a standard based on this design and it performs very well.

Schematic, PCB (Eagle format) and Gerber files are available on request.
Shera's original PIC software runs fine on my board.

Be careful with those brand-x GPS receivers though. The accuracy of
the 1pps output can be as bad as several microseconds or even worse.
The long term accuracy is probably good enough but we know nothing
about how the jitter behaves. There are GPS receivers designed specifically
for timing applications. The 1pps pulse from a Motorola Oncore UT+ doesn't
jitter more than 30ns around the true second. Brooks Shera told me that
my old Rockwell NavCore-V wasn't good enough (spec'd accuracy 1us) so
I bought an UT+ instead.

73
Johan SM6LKM