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

[Bob kb8tq]

Hi

If the TBolt is locked up and has stayed locked up for 24 hours
it should be pretty accurate. Ideally you would like to be locked
to at least 4 sats at all times for best accuracy. Lady Heather is
your friend when it comes to checking this sort of thing. 

How good is “pretty accurate”? At 8 GHz, it’s a good bet ( 99 %)
that you are under 1 Hz of error. It’s a reasonable bet (> 80%) that
you are under 0.1 Hz. Both assume a 100 second gate on your 
counter. Things degrade a bit if you go to shorter gate times. The
numbers above are conservative for most TBolts. 

The Efratom drifts (ages) enough that a 300 Hz error at 8 GHz is not
impossible. A lot depends on just how long it’s been since it last
was set on frequency. Most examples are not that far off frequency ….

Neither the TBolt *or* the LPRO should “drift” 300 to 400 Hz at 
8 GHz over any reasonable amount of time ( hours, days, weeks). 
This assumes they stay powered up and in the TBolt’s case, locked
to >4 sats. 

What to do? Best guess is the TBolt is right and the LPRO is wrong. 
Reset the LPRO so it agrees with the TBolt.

Bob

> On Aug 21, 2021, at 8:50 AM, 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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