[time-nuts] oscillators

Bob Camp lists at rtty.us
Tue Aug 28 14:55:56 EDT 2012


Hi

... then if you take a look at the status printout on a TBolt "Kalman
filter" always shows up as disabled. Thus the "who knows what they are
doing".

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Arthur Dent
Sent: Tuesday, August 28, 2012 1:02 PM
To: time-nuts at febo.com
Subject: [time-nuts] oscillators

>I don't know that there is any data showing the TBolt adjusting for aging
>during holdover. In other words: showing the holdover DAC voltage changing
>at a completely constant temperature. 
>
>Bob

I haven't seen any data either but here is information from section 5.1.2 
of the 2003 Thunderbolt manual:

"Kalman filtering is a technique that improves the performance of a GPS 
disciplined clock when GPS drops out. This state is called holdover. 
During holdover the clock relies solely on the oscillator. Oscillator 
performance is subject to two basic effects. First, changes in environmental

temperature can cause the oscillator to speed up [or] slow down. Second, the
oscillator has a natural tendency to drift over time. This is called aging. 
Both temperature and aging can be mathematically predicted. However, the 
characteristics vary from crystal to crystal. The Kalman filtering monitors
the 
unique oscillator performance over time and temperature and records this 
behavior. Then when the clock goes into holdover this filtering corrects for

these effects producing a more accurate clock. The longer a clock has
to 'train' the better the Kalman filtering performance will be. 24 hours is 
considered the minimum necessary for good performance"

-Arthur
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