[time-nuts] Question re 1pps output on the Z3805A

[David]

I can think of some possibilities with the caveat that I am not
familiar with the Z3805A units:

1. The PPS output could be damaged.
2. The PPS output could be an open collector/drain output which
requires a pull-up resistor since it can only sink current.
3. The PPS output might have trouble driving a 50 ohm transmission
line.  Try measuring it directly with a x10 oscilloscope probe and no
coaxial cable.
4. Maybe your oscilloscope is triggering on the trailing edge or some
other signal aberration so you are missing the real pulse.  Be sure to
use DC coupling for both the input *and* the trigger.  I have gotten
caught by this a few times when initially measuring PPS outputs.

You could make a simple diode/capacitor peak detector to measure the
peak output voltage with a digital multimeter.  With a typical 10 MOhm
input, I would start with a 0.1uF capacitor for a time constant of 1
second.  It will not be super accurate but might save some sanity.

On Sat, 24 Nov 2012 16:52:50 -0800 (PST), Mark Spencer
<mspencer12345 at yahoo.ca> wrote:

>Thanks all for the responses.   
>
>I am routing the signal via 50 ohm coax to the 1Meg ohm input of a 100 Mhz analog scope using dc coupling.  After some fiddling with the trigger settings I am able to observe a brief pulse every second that appears to be .15 volts above ground.   I'm not inclined to believe that the signal is actually .15 volts though.  I did try terminating the scope end of the coax with a 50 ohm load and the signal as displayed on the scope didn't change.   I recall making similar measurements in the past and seeing more reasonable results.    
>I really don't want to blow the inputs on my 5370B's hence my caution here. I did try connecting the signal to one of my 5335B's and based on the trigger settings I was able to use to get that counter to trigger I'm inclined to believe it is  3.3 or 5 volt TTL level but I'm not 100 percent sure.
>I'll have to do some more experimenting with my analog with other 1pps signal sources to gain more confidence in my measurements and or ask Santa for a digital storage scope (:
>
>Regards
>Mark Spencer