[time-nuts] Frequency Counter Choice

[Magnus Danielson]

Hi,

I second this. You can read the calibration data out of the counter and
save. I've done some experiments with that, but nothing conclusive, but
I blame my lack of patience and not a proper setup.

Do replace the battery, it is cheap and relatively easy to do.

Would you loose this calibration, through a little GPIB commands one can
write a fake value in. This will however not produce the best resu. The
calibration routine actually runs an off beat frequency and then test
different values, and look for least RMS value, because it is the
calibration point. I've not had time to replicate all that, but I did
manage to write the fake value in and at one time get rid of the CAL
LOST warning.

Cheers,
Magnus

On 2020-10-29 14:17, Azelio Boriani wrote:
> For those who have the PM6681 (aka CNT81): check the 3V memory backup
> cell and replace it before the dreaded calibration lost (CAL LOST)
> will appear on the LCD. Replace the coin cell with great care (with
> the counter powered up), see the service manual for the procedure.
> <https://archive.org/details/FLUKE_PM6681_Service_Manual>
>
> On Fri, Oct 23, 2020 at 6:17 PM Magnus Danielson <magnus at rubidium.se> wrote:
>> Hi,
>>
>> On 2020-10-22 19:13, Attila Kinali wrote:
>>> On Thu, 22 Oct 2020 11:50:08 +0000
>>> Giorgio Barinetti <giorgio at barinetti.it> wrote:
>>>
>>>> Choices are many, but I'll try to avoid the "older" machines lile 5370 or 5335. The 531xx series seems nice ( money apart )
>>>> But again : which one between the 3 ? 53131, 53132 or 53181 ?
>>> Maybe try to get hold of one of the Philips (later licensed to
>>> Fluke) PM6680 or PM6681? These are more common in Europe than
>>> in the US, so the big US dominated websites/forums/.. don't
>>> mention them that often. Solid devices that can be had as low
>>> as 300€ if you are willing to wait, 500-800€ is the usual going
>>> price. The SR620 is the workhorse that drives a lot of the
>>> time and frequency metrology worldwide and can be had new and
>>> used (new on http://thinksrs.com goes for 800-2000€ used).
>>>
>>> If you go for a new one, I would consider looking at the
>>> Pendulum CNT-90 and CNT-91. (Pendulum is the company that
>>> took over Philips frequency counter business and the CNT-90
>>> is the continuation of the PM668x line, also sold as PM6690
>>> by Fluke)
>> Let me correct on the history and geniology there.
>>
>> Philips had a instrument making side called Philips Industrier Järfälla
>> that did a range of measurement instruments. Later they joined forces
>> with Fluke. Later Philips felt that the business unit was a bad fit to
>> stay in Philips, so they sold it off to become a separate company which
>> became Pendelum. Pendelum was really the business unit with people etc
>> through that process, and the Fluke relation and rebranding continued.
>> Naturally Pendelum moved out of the Philips Industrier Järfälla office
>> over to Bälstabro (both locations in north of Stockholm) as it was sold
>> off. Pendelum also managed to rebrand their counters to Tektronix, which
>> mainly consisted of cosmetic changes to get the look and feel. Pendelum
>> was operated for many years like this, some of their production in
>> Pajala, where as other where done in Bälstabro. Later they reshaped the
>> production so that it moved to Poland where it remains. Pendulum was
>> sold to Spectracom and was operated as a subsidary for a while, until
>> they shut operation down.
>>
>> The CNT-80/81 (PM 6680 and PM6681) production went on as long as they
>> had the timing ASIC. The CNT-90 (100 ps) was developed to the CNT-91 (50
>> ps), where the later replaced the CNT-81 (50 ps). They aimed to do the
>> CNT-92, but could not at that time do it with the same technical setup.
>> They also had the Wander Meter WM-10 which aided in testing telecom
>> sync. After some testing, I suggested they would broaden the product to
>> handle more signals and that is when they mostly firmware upgraded it to
>> the WM-11, and first time I tested the WM-11 the second '1' was cut out
>> from another '10' print and put over the '0'. Also, it was still under
>> development. Several years later they where still going back to my list
>> of feedback. They later did a revamped this into a new instrument with
>> even improved capabilities such as interfaces boards. This was later
>> sold off to Calnex which sells it as Sentinel, which is a great product
>> for telecom operators.
>>
>> I still have contact with some of the Philips/Fluke/Pendelum staff and
>> owner.
>>
>> Cheers,
>> Magnus
>>
>>
>>
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