Well I have looked into this before for the 53131A, and the way signal peak volts is implemented is bizarre. I say bizarre because for low frequency, low duty cycle signals (like PPS) the 53131A will at times report the lower peak as being higher than the upper peak...

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>From the 53131A Manual: Peak volts (53131A, 53132A, 53181A) Measurement is specified on Channels 1 and 2 for dc signals; or for ac signals of frequencies between 100 Hz and 30 MHz with peak-to-peak amplitude greater than 100 mV. Results range –5.1 V to +5.1 V Resolution 10 mV Peak volts systematic uncertainty for ac signals: 25 mV + 10% of V for dc signals: 25 mV + 2% of V Well, I read the specification as being guaranteed for any DC coupled signal, in my experience even DC signals with a frequency less than 100 Hz fail to register correctly. As an example at 1 kHz (10% duty cycle) the channel 1 VPP (DC, 50 Ohm), behaves as expected: +0.00V +1.58V +0.01V +1.58V +0.01V +1.58V +0.00V +1.58V +0.00V +1.58V +0.00V +1.58V +0.00V +1.58V +0.01V +1.58V +0.00V +1.58V +0.00V +1.58V +0.01V +1.58V +0.00V +1.58V +0.00V +1.58V +0.01V +1.58V +0.00V +1.58V +0.00V +1.58V +0.00V +1.58V +0.01V +1.58V +0.00V +1.58V +0.01V +1.58V +0.00V +1.58V +0.00V +1.58V +0.00V +1.58V +0.00V +1.58V +0.01V +1.58V +0.00V +1.58V +0.00V +1.58V For 1 Hz (10% duty cycle) the channel 1 VPP (DC, 50 Ohm), behaves unexpectedly: +0.05V +0.05V +0.05V +0.05V +0.06V +1.28V +0.05V +0.05V +0.05V +0.05V +0.05V +0.08V +1.28V +0.05V <- Lower peak greater than upper peak +0.05V +0.05V +0.05V +0.05V +0.05V +1.54V +0.05V +0.05V +0.05V +0.05V +0.05V +0.05V +1.24V +0.05V <- Lower peak greater than upper peak +0.05V +0.05V +0.05V +0.05V +0.05V +0.64V +0.05V +0.05V +0.05V +0.05V +0.05V +0.05V +0.06V +1.28V So the reason auto-trigger fails, is the instrument does not set an appropriate trigger level, since the VPP reading fail to have any integrity below 100 Hz. I would be interested to see what you get on the 53132, I suspect its implementation of VPP to have the same issues. On Sat, Sep 17, 2016 at 10:28 AM, Bob Camp <kb...@n1k.org> wrote: > Hi > > Set it up on your 53132 and see what happens … > > Bob > > > On Sep 16, 2016, at 8:35 PM, Scott Stobbe <scott.j.sto...@gmail.com> > wrote: > > > > For a low duty cycle pulse, the ac coupled signal will be approximately > the > > same as if it were dc coupled. Not sure I follow what you mean. There > will > > be only one rising edge for a narrow pulse ac coupled, as the falling > edge > > occurs much quicker than the HPF time constant. > > > > On Friday, 16 September 2016, Bob kb8tq <kb...@n1k.org> wrote: > > > >> Hi > >> > >> Most PPS signals these days are very low duty cycle. If you AC couple > >> them, you can easily be triggering on the wrong edge. With the narrow > pulse > >> it may not be very obvious. > >> > >> Bob > >> > >>> On Sep 16, 2016, at 5:46 PM, Charles Steinmetz <csteinm...@yandex.com > >> <javascript:;>> wrote: > >>> > >>> Bob wrote: > >>> > >>>> Set it to: > >>>> > >>>> 1) DC coupled (AC does not go low enough) > >>>> 2) 50 ohms if your driving source will tolerate it, otherwise 1 meg > ohm. > >>>> 3) Manual trigger mode (Auto is to fast and it forgets where the > >> trigger should be) > >>>> 4) Trigger level around 1/2 the PPS P-P voltage > >>> > >>> I would just add the following: > >>> > >>> 1) I'd be very surprised if AC coupling wouldn't work fine with a > >> typical PPS pulse, which has very fast edges (low nS). No LF response > is > >> required. Indeed, AC coupling will keep any LF noise out (not that we > >> expect much in this application). This is true even if the PPS is a 50% > >> duty-cycle square wave -- the spikes that get through every 500mS, > >> alternating positive and negative, will have fast, accurate leading > edges > >> and will be way longer than necessary for proper triggering. > >>> > >>> 2) If your source will not tolerate a 50 ohm load, buffer it. Any > >> significant length of cable between the source and a 1M termination will > >> just slaughter your pulse. > >>> > >>> 4) The relevant peak voltage is the actual voltage at the counter > input > >> connector -- which may be only 1/2, or possibly even less, of the > nominal > >> logic level, depending on the source impedance. > >>> > >>> Best regards, > >>> > >>> Charles > >>> > >>> > >>> _______________________________________________ > >>> time-nuts mailing list -- time-nuts@febo.com <javascript:;> > >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >>> and follow the instructions there. > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@febo.com <javascript:;> > >> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.