On Fri, Aug 19, 2016 at 12:24 PM, Hal Murray <hmur...@megapathdsl.net> wrote: > > lister...@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. > >
Thanks to everyone for the replies, this definitely helps clear things up. I had my suspicions that I wasn't measuring what I thought I was as the resulting ADEV curve I was getting in Timelab (I forgot to mention I have a Prologix GPIB->USB interface and have been using it for logging/capture) had the '\_/' (down, flat, up) shape that I gather you get from OCXO's. I did also have a suspicion that this could lead down a slippery slope of needing another GPSDO to compare it with and then and then... ;-) (While I see there is a 5071A available on ebay right now, those are somewhat out of my budget by several orders of magnitude...) Thanks, Tim _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
