[time-nuts] Measuring 1 PPS with an HP 5335A

[Jimmy D. Burrell]

Bingo! It's working now!! Thanks to everyone on the thread.

Paul, I have to give chops to Bob on this one, even though my experience is the same as yours with respect to the preset triggers. Actually, your comments/question about the "trigger lights flashing" in concert with the 1PPS signal got me looking/thinking and no, they weren't. BTW, my 0.000001 number was meant to be Hz but I left off the units.

Both Bobs (Camp and Albert) were pointing me at the 'input'. So, I drug out the HP5335A manual and re-read about all 4 trigger levels. Auto-adjustable mode allows adjusting the trigger according to the amplitude of the input signal... a sort of percentage trigger mode, i.e. turn the trigger control clockwise to 3/4 scale and you're triggering at 75% of the signal's amplitude.

The above trigger changes combined with reconfiguring for 50ohms input signal did the trick. I'm now seeing readings like 0.999 999 983 +0.

Thanks again,

Jim...
N5SPE


On Feb 16, 2014, at 4:07 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
> 
> If you have a 50/50 duty cycle 1 pps, it’s going to work with a lot of settings. With a narrow (say 10us wide) pulse, most of the counters have auto trigger issues. If it’s already known to be reading nutty, trigger is a good place to start looking.
> 
> Bob
> 
> On Feb 16, 2014, at 4:29 PM, Paul <tic-toc at bodosom.net> wrote:
> 
>> On Sun, Feb 16, 2014 at 2:33 PM, Bob Camp <lists at rtty.us> wrote:
>> 
>>> On all these counters, you need to switch to DC input for 1 pps signals.
>>> You also need to manualy set the trigger level to something like +1.5V.
>> 
>> 
>> I can't believe I'm disagreeing with Bob Camp but this is not my
>> experience.  99.9% of the time preset trigger works fine and I think you
>> should start with that.  AC coupling almost always works and is sometimes
>> required (with the Rb I think).
>> 
>> I have a 5335A (w/ opt 010+040) and have measured 1PPS on my PRS-10, Fury,
>> Firefly and random GPS parts.  If the trigger light is not flashing at 1 Hz
>> the only thing I've ever had to do is toggle AC coupling or enable 1PPS
>> output on the device (or plug it in).  Sometimes increasing the gate time
>> tidies up the display.
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