[time-nuts] 53132A triggering

[Bob Camp]

Hi

Set it up on your 53132 and see what happens …

Bob

> On Sep 16, 2016, at 8:35 PM, Scott Stobbe <scott.j.stobbe at 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 <kb8tq at 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 <csteinmetz at 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
>>> 
>>> 
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