C'mon guys- when you speak of a frequency error in Hz, you should also specify "at what frequency" *in the same breath*. Or better yet, always specify frequency errors in relative terms.
Hundreds of Hz at 10 Mhz is unthinkable for a Rb. Even at 8.2 GHz, 100 Hz error is about 12E-9, which is likely to be outside the EFC tuning range of some (if not most) Rb standards. Both of my Rbs have a tuning range of only roughly 2E-9 via the EFC input. Outside that range, much sterner measures must be taken, which I frankly dread. The two Rbs that I own (an L-Pro and a PRS-10) both tend to drift upwards in frequency to the tune of about 1E-11 or 2E-11 per month. Superimposed on that are random variations of around 1E-11 on a time scale of a few hours. I make phase comparisons between the 10 MHz outputs of a GPSDO and the Rb under test using a simple quadrature demodulator, with the I & Q outputs displayed on a 2-chan DSO. I use the "roll mode" display feature on the DSO at its slowest speed (1000 sec/div) and just leave things running continuously for up to several days. On my DSO a full screen width is 14000 sec (slightly under 4 hours), and I just take a glance from time to time as I happen to pass by. Someone suggested a 100 sec measurement with a counter, but that is right in the realm where GPSDOs are typically the most noisy, so a single measurement is likely to have rather large errors. One would have to record a fairly large number of such measurements (several hundreds of them) and plot them out to get a good assessment of what the Rb is actually doing. WIth the IQ phase difference display, one can get a pretty decent estimate of the needed tuning correction, without doing any real work at all, in a day or so. When I'm doing something requiring the best frequency accuracy, I keep the 'scope display running while I'm doing the serious work, and note the frequency error of the Rb at the time for use in correcting the final result. BTW, I don't see much "settling" effect after making tuning changes- the correction made seems to take effect essentially immediately (as best as one can tell in the presence of GPS noise). By comparing two Rbs, I can investigate settling effects quite well without the noise having anything to do with it. Dana On Sun, Aug 22, 2021 at 8:41 AM Matthias Welwarsky <time-n...@welwarsky.de> wrote: > Hi, > > a Rb will not be long-term accurate. I'd trust a GPSDO to be long-term > accurate. A hundreds-of-Hz offset between the LPRO and the GPSDO certainly > points into the direction of the LPRO being off the mark. > > When you adjust the LPRO, be sure to give it ample time to stabilize. > > BR, > Matthias > > On Samstag, 21. August 2021 14:50:24 CEST mp...@clanbaker.org wrote: > > Hello Time-Nutters-- > > > > I am working on building a downlinking AZ/EL tracking dish set up to > > receive the 8.2 GHz telemetry from the Suomi JPSS polar orbit > > meteorological/environmental satellite. The receiver seems to be > > working OK but it periodically appears to slowly drift frequency by > > 300 Hz to 400 Hz. I need some way to accurately determine what > > the actual RX receive frequency is. > > > > I have a vintage Efratom LPRO-101 Rubidium 10 MHz oscillator. > > I originally got it thinking that it would provide a decent > > phase-lock reference for my freq-counters, o-scopes, spectrum > > analyzers and Agilent/HP vector network analyzer. > > > > The only other item I have that has (or should have) a reasonably > > accurate 10 MHz reference output is a Trimble Thunderbolt. > > However, there is a several hundred Hz freq difference between the > > Efratom and the Trimble T-bolt. > > > > My question is how do I go confirming the frequency of the T-Bolt > > or the Efratom Rubidium? The Efratom has an adjustment pot > > to fine-tune its output frequency. How do Time-Nutters go about > > confirming the accuracy of frequency references such as my > > T-Bolt or Efratom rubidium oscillator? > > > > Thanks for any feedback / suggestions on this !! > > > > Off-list communications on this via my email is OK!! > > > > Mike Baker mp...@clanbaker.org > > Micanopy/Gainesville North Central Florida > > ********************** > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe > send an > > email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow > > the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.