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Discussion of precise time and frequency measurement

Re: [time-nuts] Cheap jitter measurements

Hal Murray

Tue, Apr 3, 2018 8:06 PM

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?

What do you mean by "jitter" and what do you really want to do?

Jitter usually needs a reference. Do you have one?

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

Do you have a scope?

The Rigol DS1102E is/was quite popular and is good for close to a ns. I got
mine several years ago for $400. Looks like the going price is closer to
$300 now. It's got a USB port. You can read the data and decode it in
software.

They make lots of similar scopes. The middle 2 digits are the bandwidth: 5=>
50MHz, 10=>100MHz. The last digit is the number of channels.)

The chip in the BeagleBone series boards has extra CPUs that help with things
like this. I don't know how fast they go. I haven't seen 64 bit versions or
a lot of software activity.

--
These are my opinions. I hate spam.

gem@rellim.com said: > 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? What do you mean by "jitter" and what do you really want to do? Jitter usually needs a reference. Do you have one? > I'm thinking maybe something like a rubidium standard (FE-5680A) and a > TICC-TAPR? But that would put me out around $400. Do you have a scope? The Rigol DS1102E is/was quite popular and is good for close to a ns. I got mine several years ago for $400. Looks like the going price is closer to $300 now. It's got a USB port. You can read the data and decode it in software. They make lots of similar scopes. The middle 2 digits are the bandwidth: 5=> 50MHz, 10=>100MHz. The last digit is the number of channels.) The chip in the BeagleBone series boards has extra CPUs that help with things like this. I don't know how fast they go. I haven't seen 64 bit versions or a lot of software activity. -- These are my opinions. I hate spam.

Gary E. Miller

Wed, Apr 4, 2018 11:22 PM

Hal!

On Tue, 03 Apr 2018 13:06:43 -0700
Hal Murray hmurray@megapathdsl.net wrote:

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

What do you mean by "jitter" and what do you really want to do?

I mean jitter as NTP defines jitter. Whatever that is.

Jitter usually needs a reference. Do you have one?

I have a GPSDO, but that was why I was looking to add the Rubidium
standard to the mix.

Do you have a scope?

Yup, still got my trusty Tek 465B, and it still works fine. Cost
almost as much as a car when I bought it.

The Rigol DS1102E is/was quite popular and is good for close to a
ns.

Nice, but not quite fast enough. I've settled on the Rb+TAPR-TICC
solution.

RGDS
GARY

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@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

Hal! On Tue, 03 Apr 2018 13:06:43 -0700 Hal Murray <hmurray@megapathdsl.net> wrote: > > What would you guys suggest as the cheapest way to see jitter down > > to around 1 nano second? > > What do you mean by "jitter" and what do you really want to do? I mean jitter as NTP defines jitter. Whatever that is. > Jitter usually needs a reference. Do you have one? I have a GPSDO, but that was why I was looking to add the Rubidium standard to the mix. > Do you have a scope? Yup, still got my trusty Tek 465B, and it still works fine. Cost almost as much as a car when I bought it. > The Rigol DS1102E is/was quite popular and is good for close to a > ns. Nice, but not quite fast enough. I've settled on the Rb+TAPR-TICC solution. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 gem@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