[time-nuts] Of rubidium life and piggy-bank anemia....

John Ackermann N8UR jra at febo.com
Thu Nov 29 18:10:14 EST 2007

Hi Mike --

Most modern Rbs, and particularly the small telecom ones (which is what
most of the <$500 ones are) have a quite long lamp life; I haven't heard
of any of them failing because of lamp burnout.

However, note that those Rbs tend to have only modest short term
stability and phase noise.  In fact, the Tbolt is likely to be
significantly better in those regards than the Rb.  So swapping out the
OCXO for an Rb may not be the best move.

But on the other hand, having a free-running Rb that you calibrate
against the Tbolt (or some other reference) every so often isn't a bad
idea; it gives you a source that's independent of external factors.

Michael Baker said the following on 11/29/2007 05:31 PM:
> Greetings, all--
> As a newbie to this list, I am playing catchup
> in a number of arenas so please forgive me if
> I post something which is old news to most.
> In any event, something John Miles said pointed
> me towards investigating what it would take to
> cobble up something that would get me to the next
> higher level of frequency accuracy that exceeded my
> Trimble Thunderbolt.  My primary purpose is to have
> the most (relatively) accurate 10MHz or 100MHz frequency
> reference to use in measurements above 2GHz but
> below 24GHz.  Obviously, a somewhat anemic piggy-bank
> prohibits me from dropping several thousands of $$$ (choke)
> on a surplus cesium reference, so I am going to have to
> settle for rubidium.  I see lots of rubidium oscillators
> come and go on eBay for several hundred $$.
> I started out to see what it would take to replace the
> OCXO in my T-bolt with a rubidium oscillator.  One
> concern I had was paying $400 for a surplus rubidium
> oscillator and then discovering that it only had a year
> or two of life left in it.
> I stumbled across an interesting (but a tad dated) Air
> Force study titled:
> Observations on the Reliability of Rubidium Frequency
> Standards on Block II/IIA GPS Satellites
> It is found at:
> http://tycho.usno.navy.mil/ptti/1995/Vol%2027_10.pdf
> It may well turn out that after the tears dry following
> the realization that I probably cannot afford a tighter
> frequency reference than my T-bolt provides I will just
> have to resign myself to the E-12 of the T-Bolt
> and be happy...
> Your thoughts and comments are most welcome--
> Mike Baker
> Micanopy, Florida
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