[time-nuts] Capturing a 1PPS signal with a Keysight 53230A

[Peter Membrey]

Hi guys,

I'm looking to measure and characterize the 1PPS output of a uBlox MAX M6Q using a Keysight 53230A. Specifically, I'm mostly interested in the period of the signal, how close it is to exactly 1Hz and how that signal changes over time.

The Keysight is using the 10Mhz output of a SRS FS-725 Rubidium Frequency Reference (which is being disciplined by a PPS from a microsemi S600 GPS) as an external reference.

I've currently got the channel configured as follows:

* DC
* 50Ohm
* Bandwidth filter enabled

The default gate time is 100ms, which if I leave it configured for that, it will never show a reading. I can get it to start giving a reading if I set the gate time to 3 seconds but for reliable readings, I need to set it to at least 5 seconds.

So, here's my questions:

1. I would like to capture the period of each pulse - is this doable with my set up?
2. What does gate time actually mean? I've read a number of descriptions, but I'm still not 100% clear on what it means in this context and what impact it has
3. How exactly does the gate time work in this case? I mean if it captures data over 5 seconds and gives one reading - what actually is that reading? An average? One of the samples?
4. Should I be doing anything differently?

Ideally, what I'd like to do is capture the period of each pulse individually so that I can do an Allan variance on the data over a period of time.

I've googled around and I've read numerous guides, but they mostly seem to cover faster signals (like 10Mhz sine wave) rather than the much slower PPS. I asked a very similar question on the EEVBlog forum, and the suggestion was to use time-stamp capture with the rise time, but unfortunately, it never seems to see the signal, even though the gate indicator flashes every second.

Thanks in advance for any advice or guidance!

Kind Regards,

Peter Membrey