On Dienstag, 24. August 2021 00:00:41 CEST Dana Whitlow wrote: > I connect one signal to the LO input of the demodulator, and the other > signal to the > RF input. I should draw up a schematic of this, and will do so.
It's basically "half" of a DMTD, an "SMTD", so to speak, but without the "difference" part ;) > > Dana > > On Mon, Aug 23, 2021 at 4:59 PM Robert DiRosario <[email protected]> wrote: > > Dana, > > > > >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. > > > > Can you explain what you do? Do you just connect the two 10 MHz signals > > to the input of the demodulator? > > > > Robert > > > > On 08/22/2021 11:16 AM, Dana Whitlow wrote: > > > 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 < > > > > [email protected]> > > > > > 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 [email protected] 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 [email protected] > > >>> Micanopy/Gainesville North Central Florida > > >>> ********************** > > >>> > > >>> _______________________________________________ > > >>> time-nuts mailing list -- [email protected] -- To unsubscribe > > >> > > >> send an > > >> > > >>> email to [email protected] To unsubscribe, go to and > > > > follow > > > > >>> the instructions there. > > >> > > >> _______________________________________________ > > >> time-nuts mailing list -- [email protected] -- To unsubscribe > > > > send > > > > >> an email to [email protected] > > >> To unsubscribe, go to and follow the instructions there. > > > > > > _______________________________________________ > > > time-nuts mailing list -- [email protected] -- To unsubscribe > > > > send an email to [email protected] > > > > > To unsubscribe, go to and follow the instructions there. > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] -- To unsubscribe send > > an email to [email protected] > > To unsubscribe, go to and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] To unsubscribe, go to and follow > the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
