Hi *Assuming* that we’re talking about 4 to 6x10^-10, you should be able to do better than that with the piston trimmer. I’m in no way suggesting that it is *easy* to do better than that.
The bigger question is: how much value is there in doing better than that? What is the aging rate on the OCXO? How does it do in humidity / pressure? ( = when the weather changes). Do you leave the counter on all the time? Aging can anything from 4x10^-10 / day and down. Probably a 10 day number is a better target and it’s easier to measure. 4x10^-10 over 10 days is pretty good on a 10811 after a month or three. Humidity and pressure are the two gotcah’s in the 10811’s open box design. Humidity depends on a lot of things. Dirt on the boards is not good. Component coatings that have cracked over the years also not good. Pressure is going to depend if you just had the eye of a hurricane pass over. You can get into parts in 10^-10. If the counter is power cycled (like to keep the LED’s from dying …) then warmup on the OCXO comes into play. After a week off, you will be doing well to be within your 6x10^-10 after a couple days on power. ====== One somewhat goofy way around the super stable stuff on the EFC is to cut down on the range / sensitivity of the port. If all you need is 1x10^-9 of range, that’s a lot less than what you have on the normal EFC. It’s massively less than what you have on a unit pulled from the heater shell on one of the GPSDO’s. If you do a simple resistor L network to scale the voltage 100:1 (or more) that takes the voltage at the EFC (with 0-5V drive) down to 0 to 0.05V. Yes, some though needs to go into what you do, but it gets it out of the “crazy” end of things and into something you probably can do from junk box parts. For the brave (or crazy) there *is* another route - change the parts around the coarse trimmer to reduce it’s range. Yes you have to do it “just right” to keep the oscillator on frequency. The “old school” approach was to hand grind single plate caps for the final part that went in. Oddly enough NASA was fine with that approach. Lots of fun !! Bob > On Jul 21, 2019, at 9:53 PM, Perry Sandeen via time-nuts > <time-nuts@lists.febo.com> wrote: > > Yo Bubba Dudes!, > I bought a HP 10811 from ebay for $36 and shipping. > I installed it in my HP 5335a counter. After running continuously for about > 90 days it was down to about 4 to 6 parts in -10. I couldn't adjust it for > better accuracy as HP in their infinite and inscrutable wisdom provided a > edge connector for the 10811 but didn't make provision for EFC one had only > the course adjustment. Sheesh! > Now maybe I was very lucky in my ebay purchase. On ebay prices seem to go > from $125 to around $60. One of the lower priced sellers advertise that > their 10811's are *tested* but no details. > Regards, > Perrier > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.