[time-nuts] Cheap jitter measurements

Bob kb8tq kb8tq at n1k.org
Tue Apr 3 16:51:02 EDT 2018


Hi

I would add the HP 5335 to the list of counters to look for. The surplus market can be really 
weird. A 5334 *should* be less than a 5335, but on any given day, that may not be true. The
5370 and 5345 are also worth looking for. Target price (at least for me) wold be < $150 for a
quick buy and < $70 if I was willing to shop for a while. 

Getting data *out* of the older counters will involve GPIB. If you are not already set up to do 
that, there will be the cost of a cable and a simple adapter. 

If you want to move up a generation, the 53131 and 53132 are higher resolution devices than
the 5334 and 5335. They give you the benefit of a serial port. No GPIB stuff to bother with. 
Finding one at price lower than the TAPR counter …. probably not. 

Bob

> On Apr 3, 2018, at 3:04 PM, Tom Van Baak <tvb at leapsecond.com> wrote:
> 
> 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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