[time-nuts] Cheap jitter measurements

[Tom Van Baak]

Hi Gary,

One solution is to look for used hp, Fluke, or Racal time interval counters on eBay. 1 or 2 ns is pretty easy to find with a $100 or $200 budget. Look for Racal 1992 or hp 5334B as examples. If you plan to collect lots of data, you'll want GPIB (or RS232 / USB) connections to a PC and that will add to your net cost.

Another solution is to homebrew your own 1 ns counter. The downside is you will spend a month working out the bugs before you trust the data. Plus if you don't already have another counter to compare it against it makes development even harder.

Third solution is the TICC from TAPR. It's new and works out of the box. Lots of us use them. John did a very good job with the design. Highly recommended. It's a dual-channel *time stamping* counter so you can collect 1PPS data on two separate GPS receivers at the same time if you want. In that respect it's 2x as useful as a commercial *time interval* counter.

You mention jitter, not ADEV. I don't think you need a fancy timebase if all you want to measure is jitter. You can get a good feel for the jitter of a GPS / 1PPS output within a few samples. Even a minute of data is usually enough to establish the rms jitter value. If you want a full ADEV plot, then yes, you'd probably want at least an Rb for your reference.

See paragraph "Timing Stability" at http://leapsecond.com/pages/MG1613S/ for an example of what jitter from a GPS receiver looks like; in this case it's primarily sawtooth.

Right, the picPET has 400 ns resolution and so it is not the right tool for your nanosecond needs. I do have a 10 ns version that I use, but that's still a bit coarse for GPS work.

I have spare FEI Rb here; I'll send it if you want it. That way you can afford a TICC.

/tvb


----- Original Message ----- 
From: "Gary E. Miller" <gem at rellim.com>
To: "time-nuts" <time-nuts at febo.com>
Sent: Tuesday, April 03, 2018 10:47 AM
Subject: [time-nuts] Cheap jitter measurements


Time-nuts!

With care I can measure GPS jitter on a RasPi to a bit over 300 nano sec
resolution.  That is the smallest increment of the RasPi 3B clock with
a 64-bit kernel.  That is clearly not time-nuts accuracy.

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

I'm thinking maybe something like a rubidium standard (FE-5680A) and
a TICC-TAPR?  But that would put me out around $400.

The picPET does not look accurate enough.  Maybe a clever way to use it
for more accuracy?  Is there a picPET like thing cheaper than the
TICC-TAPR?

Ideas?

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem at rellim.com  Tel:+1 541 382 8588

    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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