Thread: Homebrew GPSDO
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Old 6th Mar 2021, 1:50 am   #14
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 2,369
Default Re: Homebrew GPSDO

If you want to really compare the agreement between two 10MHz oscillators and you don't want to wait for ages you could try and borrow an old HP8405A vector voltmeter.

In my old youtube video below I tried to adjust two Agilent ESGD signal generators to be as close as possible using the calibration interface for the internal 1E5 OCXO. One OCXO is fed to channel A and one is fed to channel B of the old HP8405A VVM.

In the video you can see I managed to get 1 degree of phase slip in about 8 seconds. This is a difference of just 0.00035Hz between the two oscillators.

If it slipped 360 degrees in 1 second then that would be a 1Hz error as it slips a whole cycle in 1 second.

Therefore a 1 degree slip in 1 second would mean 1/360 Hz difference = 0.00278Hz.

1 degree in 8 seconds is 8 times better than this at 0.00035Hz.

This is much faster than waiting for a long time to look for a cycle slip on a scope for example. It would also be possible to hook the phase recorder output at the back to a DVM so the error could be logged over time to look at the short term drift characteristic.
Regards, Jeremy G0HZU
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