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

Sat Aug 28 08:19:16 UTC 2021

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 <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
> > >>> **********************
> > >>> 
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