[time-nuts] TBolt OCXO replacement

Bob Camp lists at cq.nu
Tue Feb 16 23:52:48 UTC 2010


Hi

Nothing is ever perfect. 

The "magic" can only do just so well. The lower the aging rate, the better the result after correction. 

A little more detail:

Take a number, maybe 10 ns and call it the "error" of the GPS signal. Over a 1 second period, that' s not so good (10 ppb). Over 10,000 seconds (~3 hours) it's better (1 ppt). Wait for a day and it's quite good (0.1 ppt). Wait a couple of weeks and it's tough to beat (< 1.0 x 10^-14). If you take a different number for error all of that will directly scale. 

The problem is - all of that takes *time*. The more stable the OCXO the better it can smooth out the variations in GPS. That of course assumes that you crank out the time constant of the loop to make that be true. 

Bob


On Feb 16, 2010, at 6:28 PM, Henry Hallam wrote:

> Timing newbie here, so please educate me - why does aging matter?
> Isn't the whole purpose of a GPSDO to completely eliminate long-term
> drift?
> 
> Thanks
> Henry
> 
> On Tue, Feb 16, 2010 at 2:36 PM, Bob Camp <lists at cq.nu> wrote:
>> Hi
>> 
>> A similar question though would be - once you have done all the
>> "corrections" to the setup of the TBolt (damping, time constant,
>> sensitivity) what's left to fix?
>> 
>> I would *guess*:
>> 
>> Lower aging
>> Better TC
>> Better short term
>> 
>> Aging will likely get better the longer you leave the existing oscillator on
>> power. You also may be able to pick between units to find the best of 4 or
>> something like that.
>> 
>> TC can be improved a number of ways simply by "helping" the existing part. I
>> think we have gone over that in about 300,000 messages so far.
>> 
>> Short term stability is about the only thing I can see that's still on the
>> list.
>> 
>> That gets you to the question - just how good do you think the 1 second AVAR
>> is on the existing oscillator, independent of the TBolt environment?
>> 
>> If for instance you have a 2.5x10^-12 OCXO in yours, you would only see a
>> significant improvement with a sub 1.0x10^-12 OCXO. That sort of bounds your
>> OCXO shopping list right there.
>> 
>> Bob
>> 
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Scott Newell
>> Sent: Tuesday, February 16, 2010 1:06 PM
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] TBolt OCXO replacement
>> 
>> At 11:37 AM 2/16/2010 , WarrenS wrote:
>>> 
>>> In the ever ending battle to improve my TBolt's performance, I am in the
>> process of upgrading a OCXO replacement I did to it a while back.
>>> It would be Interesting to hear suggestions from others that have done
>> similar sort of things and the results they have achieved.
>> 
>> Did you check out John Miles's writeup?
>> 
>> http://www.thegleam.com/ke5fx/tbolt.htm
>> 
>> 
>> 
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>> 
>> 
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> 
> 
> 
> -- 
> Henry Hallam
> 
> Sent from my Laptop
> 
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