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

Anders Wallin anders.e.e.wallin at gmail.com
Mon May 2 13:10:06 EDT 2016


4.
With 1PPS you probably want to run it in time-interval mode and measure the
phase difference of  two clocks: have it start on CH1 with (say) the 1PPS
from your microsemi, and stop on CH2 with your uBlox.
You should still have it on ext-REF with 10MHz from the Rb-clock.

gate time refers to measurements in frequency counter mode, usually not
used with 1PPS signals.

On Mon, May 2, 2016 at 2:09 PM, Peter Membrey <peter at membrey.hk> wrote:

> 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
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