[time-nuts] 1PPS questions

[VE7HR]

Hi Dana,
I will look closer at the 1 PPS.  
I found I had the scope setup wrong and the 1 PPS is 3.84V when terminated in 50 Ohms.  
And about 5V with overshoot when terminates in a higher impedance.  I will take some measurements and determine the output impedance of the GPSDO 1PPS and design a suitable pad.  Since the pods of the 5372A are always terminated in 50 Ohms the risk of damage is much less.  

I will also look at how HP did the 2.5:1 attenuator in the pod.  It might be a good place to start on an external attenuator design. 

Thanks for suggestions.  

Dave
VE7HR 

Sent from my iPhone

> On Jul 2, 2020, at 10:53 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> I like Bob's suggestion about using an L-pad.  Even if the line driver *is*
> happy driving
> 50 ohm line (which I was admittedly assuming), the L-pad approach will keep
> the
> driver cooler which will likely reduce warmup drift of its propagation
> delay as well as
> extend its lifetime.
> 
> Dana
> 
> 
>> On Thu, Jul 2, 2020 at 9:20 AM Bob kb8tq <kb8tq at n1k.org> wrote:
>> 
>> Hi
>> 
>> Probably the easiest approach is an L pad at the input to the measurement
>> device.
>> Something like a 470 ohm in series and a 120 ohm to ground. A 50 ohm pad
>> may not make the line driver in the source device very happy ….
>> 
>> Something more exotic would be to do a distribution amp. Use a NC7SZ125 at
>> the
>> input so it’s 5V tolerant. Run however many of them you need to drive the
>> desired
>> number of outputs.  Power it all off of 2V and you have 2V p-p output(s).
>> 
>> Keep in mind that 2V p-p “logic” signals may or may not trigger CMOS level
>> stuff
>> powered off of 3.3V. CMOS running on 5V gets into the “not going to
>> happen”
>> area.
>> 
>> Bob
>> 
>> 
>> 
>>>> On Jul 1, 2020, at 9:37 PM, VE7HR <ve7hr at ve7hr.ca> wrote:
>>> 
>>> Are there any suggested method to reduce your 1 PPS signal to a safe
>> level for your test equipment?
>>> It seems like my HP Z8316A is outputting slightly more than 5V into 50
>> Ohms.
>>> 
>>> Up till now I have been using a 10 MHz output from the Z3816A. But I
>> understand 1PPS is a better signal to put to Channel A.
>>> 
>>> My HP 5372A seems to default to 2V Max level if you hit instrument
>> default.  I am starting to like it so I don’t want to trash an input
>> module.
>>> 
>>> I think I might try a TICC in the near future but for now I will have to
>> slum with the vintage HP iron.
>>> 
>>> Thanks
>>> Dave
>>> VE7HR
>>> 
>>> Sent from my iPhone
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