[time-nuts] 53132A triggering

[Tom Miller]

----- Original Message ----- 
From: "Charles Steinmetz" <csteinmetz at yandex.com>
To: <time-nuts at febo.com>
Sent: Friday, September 16, 2016 5:46 PM
Subject: Re: [time-nuts] 53132A triggering


> 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
>
>
> _______________________________________________

Don't forget to select positive edge.