[time-nuts] Scopes and 1 PPS signals?
tractorb at ihug.co.nz
Wed Oct 24 00:21:15 EDT 2007
----- Original Message -----
From: "Didier Juges" <didier at cox.net>
To: "'Discussion of precise time and frequency measurement'"
<time-nuts at febo.com>
Sent: Wednesday, October 24, 2007 3:58 PM
Subject: Re: [time-nuts] Scopes and 1 PPS signals?
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+tractorb=ihug.co.nz at febo.com RETRY
> I took some pictures of my Thunderbolt's PPS output. While it's
> pulse is not
> quite as narrow as what you report, it's 10uS, way too narrow for
> the scope
> to display it in normal ("Sample") mode at 250mS/div (the fastest
> that will allow to measure the period of a PPS signal) on my TDS-210
> storage scope.
> There are at
> The names are self explanatory, but just in case :-)
> 1_PPS_10xProbe is the PPS measured at the end of a 3 foot cable with
> a 10x
> 2_PPS_Sample Mode is the PPS signal in normal (sample) mode, as you
> would see it on any DSO without any special mode. It's fair to say
> it would
> be hard to make sure what you are seing or measuring. Please note
> that some
> of the time, the scope triggers, but the trace is flat. I had to
> wait to
> make this shot, which was the best I saw in about 30 seconds.
> 3_PPS_PeakDetect_Mode is the same signal, with the scope in
> mode. It is easy to check the period (if not very acurate). In this
> all sweeps look the same.
> 4_PPS_Diode is with a 1N4148 between the PPS output and the scope
> probe. See
> how the 10uS pulse is now a solid 250uS at 1/3 the height. It would
> be much
> easier to see on any scope, I need to pull the old trusty Tek 2245A
> and see
> what it does on it.
> 5_PPS_Diode_5.6nF is the same diode with a 5600pF capacitor across
> probe. The pulse is now strecthed to ~10mS.
> 6_PPS_Diode_5.6nF is the same signal at the 250mS/div sweep rate.
> That's a heck of a lot cheaper than $45. Does not even need a power
> Didier KO4BB
I took Brookes original inquiry to be about measuring the width of the
nominally 10 uS wide PPS pulse-in which case anything that alters the
pulse width is a no-no. Precise and stable triggering delay to place
one of the pulses in the on-screen area is all that is required.
More information about the time-nuts