[time-nuts] 53132A triggering

Charles Steinmetz csteinmetz at yandex.com
Fri Sep 16 17:46:43 EDT 2016

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,


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