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

[Didier Juges]

So, is it a case where someone who has a Thunderbolt and a telco grade Rb
should use the TB for normal use when GPS is up and use it to resync the Rb
on occasion, so that the Rb can be used as a backup when the GPS goes out? 

Should the Rb be phase locked to the TB with a very long time constant, and
if so, how long?

I guess the answer is: plot the Allan Variance of the Rb, knowing what that
of the TB is, and you know the answer :-)

The problem is, if you only have a TB and an Rb, how do you plot the Allan
Variance? Borrow tvb's Cesium?

In favor of the TB, I may point out that the power consumption of a Rb
oscillator is not negligible, compared to that of most GPSDOs. If you are
concerned about heat or power consumption, you may want to consider that.

Didier KO4BB

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of John Ackermann N8UR
> Sent: Thursday, November 29, 2007 5:10 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Of rubidium life and piggy-bank anemia....
> 
> 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.
> 
> John