[time-nuts] Yet another GPSDO - locking to 10MHz

Murray Greenman Murray.Greenman at rakon.com
Sun Jun 27 15:14:22 EDT 2010


I have a design which locks a high performance 10MHz OCXO to a 10MHz
source which should work equally well with the LEA5, or any source of 5
or 10MHz.

I designed it for use with a distributed factory GPS reference which has
picked up noise, hum and phase modulation, in order to deliver a high
quality but GPS locked reference direct to equipment. The design adds
nearly three orders of improvement.

Essentially it divides the incoming 10MHz by 16384 and compared the
phase with a similar division from the OCXO, within an ATTiny2313 micro.
The phase detector is a D-flip-flop type implemented in software (in
interrupts), and it delivers a locked reference with ADev around 10e-12
for Tau between 1s and 20s. The micro also keeps a real time clock and
does various background monitoring and telemetry tasks. There is PC
monitoring software as well. There are only four chips in the design.
While I can't share the code (belongs to my employer), the idea is
simple enough and I could share the schematic.

Eight of these units have been built. I used the excellent Rakon
STP2402E OCXO.


Regards,
Murray Greenman ZL1BPU





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