[time-nuts] Expected 10 MHz offset from a GPSDO?

Hal Murray hmurray at megapathdsl.net
Fri Aug 19 15:24:35 EDT 2016

listertim at gmail.com said:
> Connecting the 10 MHz output to the Channel A input (on the 5334B) or the
> frequency input (on the 5370B) and setting 50 Ohm termination and AC signals
> but without any other input or external reference results in a frequency
> that is off by about 0.1-0.2 Hz. Is this amount of offset expected or a sign
> something is not right with the GPSDO? 

Your GPSDO is more accurate than your counter.  You are measuring the 
frequency offset of the crystal in the counter rather than the GPSDO.

You may have to stand on your head to understand what I'm trying to say.  It 
will be obvious once you see it.

If/when you power cycle the GPSDO (without power cycling the counter) you can 
watch it shift when it locks up to GPS.  If you disconnect the antenna it 
will stay unlocked and you can watch the crystal in the GPSDO drift as it 
warms up.

If you unplug the counter for a while but leave the GPSDO powered on, you can 
watch the crystal in the counter warm up.  (Turning it off isn't good enough, 
it keeps the crystal warm even when the switch says off.)

If you have a GPIB connection to the 5334B, you can get a few more digits by 
asking it to count for 99 seconds.  If you get that working and your lab is 
not air conditioned, you can see the temperature effects on the 5334B.

These are my opinions.  I hate spam.

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