Hi

I guess the first question would be - If you have a Time Pod, what do you need a counter for?

Based on a guess that you need extended frequency range, either would do pretty well. My vote
would go to the HP for a couple of reasons:

1. It’s more broadly supported in terms of driver software (which may or may not matter to you).

2. It’s a more common item on the auction sites, so parts are easier to find.

3. It shares some parts (like the power supply) with the (cheaper) 53181

No those are not great big reasons to go for one over the other. They are very similar devices. One
has an LCD that has a finite life. The other has a VFD that also has a finite life. Both are custom, that’s
a tie. Some like the command (button) arrangement on one over the other. I think it’s more a “what
are you used to” thing than anything else. On the 53131 you need to hit the Run button in some cases.

I have not watched the prices on the Fluke. I have kept track of the 53131’s. A “good price” on one
these days is below $600 ( = you may need to shop a bit, but they do show up).

Bob

Thanks Bob

I'm using the actual time pod for paying activities.  This would be a counter for time nuttery using the time pod software.  In those cases Where I don't want to fire up the 5071.

I'm familiar with the Keysight counters and I have a lot of them into the high Ghz ranges

The 53131 is spec'd to 500ps and the  6680 is spec'd at 250ps

I've also been leaning in the 53131 direction but I'd like to have the best tool for the job at hand

Content by Scott
Typos by Siri

On Sun, November 15, 2015 3:59 pm, Bob Camp wrote:

Or was the original question a slip, and was supposed to be which counter
is good for use with TimeLab software?

--
Chris Caudle

More of a slip as I've noted I have a time pod for work but I'd like to add a small counter for time nuttery as power is not cheap in NE so running the 5371A for long runs can get expensive

Content by Scott
Typos by Siri

Why would you want to use a 150 ps 53131 instead of a counter/timer like
the Agilent/Keysight 53230A that provides 20 ps resolution? The TimePod
my have better noise specs but it is a really dedicated, specific-use
device.

Larry

On 11/15/2015 10:42 PM, Scott McGrath wrote:

--
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)

On Mon, November 16, 2015 12:42 am, Scott McGrath wrote:

I don't follow.  Why would you not use the TimePod with a lower power
reference?  It isn't like a TimePod only works with a cesium clock as the
reference source.

--
Chris Caudle

Hi,

PM6681's turn up at quite a good price too, and you get a lot of
extras over the 6680 - does anyone know if Timelab will work with a
6681?

Angus.

On Sun, 15 Nov 2015 15:10:42 -0800, you wrote:

Hi

At leas on the spec sheet I found, both counters have a single shot of 500 ps. The
6680 “improves” as the averaging goes up.

http://isurplus.com.au/specifications/Philips%20PM6680%20Specifications.pdf

Section 13-8 has a lot of “500 ps / sqrt(N)" in it. If N=1 (single shot) you get 500 ps. HP stops the
process when resolution and random bounce are roughly equal. Fluke gives you another bit of
noise to possibly average out under some conditions.

At least the way I read the data sheets, the two counters are very similar.

Bob

5371a is a TI analyzer  The time pod itself is used for paying work so it's not available for time nuttery.

Content by Scott
Typos by Siri

Bob,

The single-shot does not improve, it's 500 ps, but the averaging of N
samples give you that result. The 53131 does similar tricks.

Cheers,
Magnus

On 11/17/2015 02:27 AM, Bob Camp wrote:

Hi Angus,

I have three 6681s operating concurrently under a single instance of
timelab beta. It operates perfectly, even live n-cornered measurements.
Kudos to John!

The only downside (and I understand why it's this way) is that each
counter needs a unique GPIB interface, but this is a timelab requirement
and nothing to do with the counters.

My only fear regarding the counters is that I'll lose the cal one day,
so I'm keen to discover how we can calibrate them ourselves.

Cheers,

david

On 17/11/2015 7:32 AM, Angus wrote:

Not necessarily, if you follow the service manual's procedure, you can
replace the backup 3V cell safely, keeping the calibration data: the
problem is checking periodically the backup cell or replacing it
regularly (say, every 5 years).

On Tue, Nov 17, 2015 at 12:33 PM, davidh dhooke@gmail.com wrote:

Not necessarily, if you follow the service manual's procedure, you can
replace the backup 3V cell safely, keeping the calibration data: the
problem is checking periodically the backup cell or replacing it
regularly (say, every 5 years).

On Tue, Nov 17, 2015 at 12:33 PM, davidh dhooke@gmail.com wrote:

Bob,

To illustrate your point.

The original PM6681 calibration setup includes a PC, an ancient Philips
ISA-bus GPIB interface and an ancient Philips driver and a DOS program.
Collecting these and put them together to work will be an interesting
challenge.

A more modern variant of the calibration routines run can run on more
modern HW and LabView software. Philips PM5781 and Agilent 81112A pulse
generators is supported by those routines.

By now the production of the counter has stopped, as the counter core
ASIC ran out of stock.

The folks who designed and maintained them does not work there anymore.

Turns out the core setup requires a generator that creates a skewed
frequency such that you sweep over the interpolation phases. You tweak
the calibration value (3.86-4.50 ns in 0.02 ns steps) that you set over
GPIB using the *PUD command. You can check it yourself using *PUD?.
It sweeps over this range and checks for the value giving lowest RMS
value (SDEV result) and then sets this as the final value.

You can set the value using the command :SYST:UNPR;*PUD %s where %s is
the string, looking somewhat like this:

FACTORY CALIBRATED: %s%s, CALPLS 3.98 ns

The two %s in there is for some string and date, I just don't bother to
dig up a correct example.

Anyway, you can actually read-out the data and write it back without the
software. It should be possible to do something with the existing pieces
and it might be possible to actually get the calibration software
operational again.

I just don't have a CNT81 anymore to try this out on.

Cheers,
Magnus

On 11/18/2015 01:35 PM, Bob Camp wrote: