[time-nuts] Cheap jitter measurements

Lars Walenius lars.walenius at hotmail.com
Wed Apr 4 13:33:03 EDT 2018


I would say my implementation is simpler than Nick’s:
https://www.eevblog.com/forum/projects/lars-diy-gpsdo-with-arduino-and-1ns-resolution-tic/?all . It is just an Arduino+ two HCMOS and a few passive components.
>From the beginning Nick copied my interpolator. Later he added a FET that might act as a constant current generator but I doubt it works very well. At least the variance of the FET’s are to large. The temperature stability is not that good either. So far I have not seen any tests of this. The Elektor GPS by Joost Breed copied Nick’s interpolator and a graph from that shows large non-linearities as I can see.
My simple interpolator that I linearize in software is not perfect but able to get down to about 1ns linearity by setting min-max and a square term. By using Tom Van Baak’s PICDIV 26 it is fairly easy to set the linearity. Information is in the instruction found on EEVblog. In the last pages I also enclosed ADEV, TDEV and a frequency plot direct from Timelab that works very well with the controller. ADEV at 1s is 8E-10.
Also I don’t think Nick sends out the ns direct (absolutely not linearized) on the serial port as I do. As I said before this works very well with timelab.
After a lot of testing I also thinks both my hardware and software is robust.
Otherwise I would recommend the TAPR-TICC that I nowadays use more than my 5370. Good resolution and much lower power dissipation.
Lars

>From: Attila Kinali<mailto:attila at kinali.ch>
Sent: den 3 april 2018 21:04

On Tue, 3 Apr 2018 10:47:37 -0700
"Gary E. Miller" <gem at rellim.com> wrote:

>> What would you guys suggest as the cheapest way to see jitter down to
>> around 1 nano second?

Look at Nick Sayers GPSDO and his interpolator. You wont get any
cheaper than that. Next best thing is to use a TDC7200 like in
the TICC.

Of course, you will need a standard that is stable enough on the
time scales you are looking at. Which is for short taus (<100s)
a good OCXO and for 1s to 10ks an Rb, and beyond that a Cs beam
standard or hydrogen maser.

                                Attila Kinali

--
<JaberWorky>    The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.
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