[time-nuts] Scopes and 1 PPS signals?

[Didier Juges]

Glad it works. I found the same here and that's why the better pictures were
made with a 5600pF cap that just happened to lay on the bench...

Didier 

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Brooke Clarke
> Sent: Thursday, October 25, 2007 1:25 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Scopes and 1 PPS signals?
> 
> 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
> > 
> > 
> > 
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> 
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