[time-nuts] Re: Instruments for 1PPS accuracy measurement

[Magnus Danielson]

Hi,

As you begin, you can start out with a very simple setup and learn a 
lot. Then you will discover what will be your biggest limit and progress 
from there.

As measurement setup I suggest a very basic setup to get you started:

1) A GPSDO/GNSSDO reference. There is naturally a wide selection, but 
getting started with a Thunderbolt is not a bad start. You will probably 
want to use the Lady Heather software to monitor things, so any receiver 
well adapted to that would be a recommended start.

2) A time-interval counter. There can be range of these, but the key 
thing is you measure your device under test as a time-interval measure 
compared to the reference. The better time resolution, the lower 
measurement floor. The first part of the curve will be dominated by 
measurement limits. We end up paying dearly for that, but even fairly 
simple ones can be a joy.

3) Time difference recording, some form of interface over to a computer, 
typically GPIB, and running TimeLab software.

A few counters to look at: 53132A, SR620, TAPR TICC

When measuring PPS, some counters auto-tuning is "too quick" so you need 
to turn that off and set trigger points yourself for robust reading.

Comparing two PPSes to each other can be a challenge to some counters, 
so time-stamp against a clock of higher frequency can be a good 
solution. Letting TimeLab know which frequency on the stop channel, and 
it can safely unwrap cycle slips. The PPS is driven to start channel in 
this case, and that will act as timebase also.

There is a certain learning in how to tune a setup up to always give 
robust readings.

Cheers,
Magnus

On 2024-09-04 12:33, jelveh_t--- via time-nuts wrote:
> HiI am new to time and frequency measurements.
> I want an instrument to measure and compare 1PPS stability and 
> accuracy of different GPSDOs and GPS modules.I did not see any advice 
> or help on the site for the instruments suitable for these type of 
> measurements.Would you mind helping me find a list of suitable 
> instruments? It would be appreciated if the price and lead time of 
> each instrument is provided, as well.Thank you for helping me.
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