[time-nuts] rapid startup GPSDO

WarrenS warrensjmail-one at yahoo.com
Wed Jul 14 11:54:42 EDT 2010

For fast TBOLT start up
If you are not moving it, SAVE the location.

Mine finds the first Sat in about 30 seconds and phase locks in under 2 
minutes after a brief power down.
(If the Osc oven is already warmed up)

If you are moving it a lot, or if it is the first time, so it does not know 
where it is
A few changes to the default settings can help a lot.
I changed the AMU to 2 so that it picks up all the weak sats if the antenna 
is not so good
AND CHANGED THE default survey size to 50 or less.
Does not give the best results, but it gets something working fast.

What may also help is if there is a way to save the current Almanac
I do not know how to do that. It takes a good 15 min to get a new one after 
power up.


[time-nuts] rapid startup GPSDO
David C. Partridge david.partridge at perdrix.co.uk
Wed Jul 14 14:21:44 UTC 2010

After a forced cold start in an unknown location, the TB will still be 
searching for satellites after five minutes.

If you move it and don't clear the incorrect location, I don't know how long 
it will take to realise it is wrong (if it ever does).

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] 
On Behalf Of jimlux
Sent: 14 July 2010 14:43
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] rapid startup GPSDO

Is there some (inexpensive) GPSDO that has a "time from power on in an 
unknown location to reasonably stable" in the <5 minute category?

Frequency accuracy in the 1E-9 range would be fine.

A regular old GPS has a Time to First Fix well under that, and it should be 
cranking out 1pps pulses with 1E-7 or 1E-8  precision pretty quickly.. Would 
it be fair to say that after 100 seconds, one could theoretically have 
driven that down another factor of 10?

As I understand it, a thunderbolt needs some number of hours after turn on 
to stabilize, but just how bad is it after, say, 5 minutes. 

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