listertim@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.

On Fri, Aug 19, 2016 at 12:24 PM, Hal Murray <hmurray@megapathdsl.net> wrote: > > listertim@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