[time-nuts] Re: Efratom LPRO-101 Rubidium question....

[Dana Whitlow]

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.

Dana


On Mon, Aug 23, 2021 at 4:59 PM Robert DiRosario <ka3zyx at comcast.net> 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 <
> time-nuts at 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 mpb45 at 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   mpb45 at clanbaker.org
> >>> Micanopy/Gainesville  North Central Florida
> >>> **********************
> >>>
> >>> _______________________________________________
> >>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe
> >> send an
> >>> email to time-nuts-leave at lists.febo.com To unsubscribe, go to and
> follow
> >>> the instructions there.
> >>
> >>
> >> _______________________________________________
> >> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe
> send
> >> an email to time-nuts-leave at lists.febo.com
> >> To unsubscribe, go to and follow the instructions there.
> >>
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe
> send an email to time-nuts-leave at lists.febo.com
> > To unsubscribe, go to and follow the instructions there.
> >
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send
> an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.
>