[time-nuts] Scopes and 1 PPS signals?

Brooke Clarke brooke at pacific.net
Thu Oct 25 14:25:10 EDT 2007


Hi Didier:

When just a diode is used the stretching is only at the bottom of the trailing 
edge and not enough to help.  But when a little capacitance is added it works.

The period is the same as what the SR620 reported, 1/ 32 Hz.  Seems a strange 
number.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam


Didier Juges wrote:
> Some DSOs (my lowly Tek 210 does) have a peak detect acquisition mode where
> it will analyze the signal at the highest speed of the A/D converter
> regardless of sweep speed and report the min and max for each displayed
> pixel line. Main advantages are 1) to make aliasing obvious and 2) to be
> able to see very narrow pulses at low sweep speed. I can see 20nS wide
> pulses at 1 PPS easily. Of course, the precision of the measurement (if you
> use the period function) is limited to the display resolution, but at least
> you can get in the ballpark. My scope is in that mode all the time, little
> reason not to.
> 
> If you do not have such mode, put a diode (i.e. 1N4148) in series with the
> probe. The diode will charge the input capacitance of the probe, which will
> discharge exponentially in the 10 Mohm resistance and give you something you
> can see. Can't beat that for cost. Add some capacitance in parallel with the
> probe if needed to widen the pulse.
> 
> Didier KO4BB
> 
> 
>>-----Original Message-----
>>From: time-nuts-bounces at febo.com 
>>[mailto:time-nuts-bounces at febo.com] On Behalf Of Brooke Clarke
>>Sent: Tuesday, October 23, 2007 6:24 PM
>>To: Discussion of precise time and frequency measurement
>>Subject: Re: [time-nuts] Scopes and 1 PPS signals?
>>
>>Hi Bill:
>>
>>I'm sure that would work, but it's something else that needs 
>>to be done sometime in the future.
>>
>>I checked the pulse coming from the M12+T and it's more like 
>>100 ms wide, probably for this reason.
>>
>>Have Fun,
>>
>>Brooke Clarke
>>http://www.PRC68.com
>>http://www.precisionclock.com
>>http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam
>>
>>
>>WB6BNQ wrote:
>>
>>>Hi Brook,
>>>
>>>You could try using a 74123 (or newer variants) 
>>
>>retriggerable one shot 
>>
>>>to extend the pulse width to a level that would allow you 
>>
>>to see it on the scope.
>>
>>>Bill....WB6BNQ
>>>
>>>Brooke Clarke wrote:
>>>
>>>
>>>
>>>>Hi:
>>>>
>>>>While trying to figure out the O-1814 Rb source I found a 1 
>>
>>PPS signal 
>>
>>>>that's less than 10 us wide.  But using an HP 54501A DSO 
>>
>>it's almost 
>>
>>>>impossible to determine the period.  
>>>>http://www.prc68.com/I/O1814.shtml
>>>>
>>>>If the display is 1,000 dots wide:
>>>>at 2 us/sq the trace takes up about 4.5 squares or 450 dots, at 200 
>>>>us/sq the trace takes up about 0.045 squares or 4 dots but 
>>
>>the second 
>>
>>>>pulse is way off screen.  At slower sweep speeds you can't 
>>
>>see the pulse.
>>
>>>>Are there scopes that allow the period of a narrow pulse to be 
>>>>measured that don't cost an arm and leg?
>>>>
>>>>--
>>>>Have Fun,
>>>>
>>>>Brooke Clarke
> 
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> 



More information about the time-nuts mailing list