); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY
----- Original Message ----- From: "Didier Juges" <[EMAIL PROTECTED]> To: "'Discussion of precise time and frequency measurement'" <[email protected]> Sent: Wednesday, October 24, 2007 3:58 PM Subject: Re: [time-nuts] Scopes and 1 PPS signals? > ); SAEximRunCond expanded to false > Errors-To: [EMAIL PROTECTED] 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 > setting > that will allow to measure the period of a PPS signal) on my TDS-210 > digital > storage scope. > > There are at > http://www.ko4bb.com/Test_Equipment/Thunderbolt/PulseStretching > > 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 > probe > > 2_PPS_Sample Mode is the PPS signal in normal (sample) mode, as you > probably > 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 > Peak-Detect > mode. It is easy to check the period (if not very acurate). In this > mode, > 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 > the > 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 > supply > :-) > > 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. DaveB, NZ _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
