[time-nuts] How does sawtooth compensation work?

Tom Van Baak tvb at LeapSecond.com
Tue Jul 19 01:01:01 EDT 2016

> It would be interesting to look at the data to see if you can find the sort 

Hi Hal,

There's lots of examples of sawtooth patterns at: http://leapsecond.com/pages/MG1613S/

In particular there's this monster: http://leapsecond.com/pages/MG1613S/tic-72-hour.gif

It's simple for a microprocessor-based GPSDO with its TIC to realize when it's getting too lost in a hanging bridge. There are a number of ways around the problem. My favorite is gluing a resistor on top of the GPS chip and pumping a few tens of mW through it when you want the bridge to stop.

Here's the proof-of-concept: http://leapsecond.com/pages/vp/heater.htm


----- Original Message ----- 
From: "Hal Murray" <hmurray at megapathdsl.net>
To: "Nick Sayer" <nsayer at kfu.com>
Cc: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>; "Hal Murray" <hmurray at megapathdsl.net>
Sent: Monday, July 18, 2016 9:41 PM
Subject: Re: [time-nuts] How does sawtooth compensation work?

> nsayer at kfu.com said:
>> Yes, thatâ?Ts true. Given the facilities I have available with the present
>> hardware, I donâ?Tt believe I have much choice. I am not confident that I
>> could tell the difference between noise in the phase detection system and
>> PPS jitter variations that small. If the PA6H receiver gave sawtooth
>> corrections, Iâ?Td be able to do better. 
> It would be interesting to look at the data to see if you can find the sort 
> of pattern that a sawtooth correction would help and where a hanging bridge 
> might cause confusion.
> If the bridge isn't hanging, the data samples should be spread over a range 
> that is the clock period of the GPS unit.  Round that up to 100 ns.  I doubt 
> if you will see that with a PC.
> On the other hand, you can get the same sort of pattern with a PPS over USB.  
> That would be a ms wide and easy for a PC to get time stamps much finer 
> grained than that.
> -- 
> These are my opinions.  I hate spam.

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