If you use a Tektronix TDS series scope you can set the acquiring to "peak detect" instead of sample to let the PPS be visible even for long timebase run. That is: usually, with the trigger set to "normal" and the timebase to 100nS/div or 1uS/div you can see the PPS anyway. If you set the timebase to 100mS/div then you can no longer see the pulse even if the trigger triggers the scan: setting the acquire to "peak detect" then the pulse returns visible and you can see the repetition rate.
On Thu, Jan 5, 2012 at 7:17 PM, Chris Albertson <albertson.ch...@gmail.com>wrote: > On Thu, Jan 5, 2012 at 9:46 AM, beale <be...@bealecorner.com> wrote: > > > I think there is something funny about the 1 PPS output on pin 6 from the > > currently available cheap FE-5680A units. I have three of these units. On > > one unit, on one occasion, I did observe a logic-level 1 PPS pulse, > exactly > > 1 microsecond wide. But after a power cycle it never came back, although > > the unit indicates a locked condition, and is apparently working. The > other > > two units also seem to work (10 MHz output OK, lock OK) but I have never > > seen a 1 PPS signal on pin 6 from them. My Tek TDS-210 is easily capable > of > > triggering on and displaying a 1 usec pulse. Is it possible the pulse > > appears only after a RS-232 command, or after some other special > condition? > > > I think the signal is there, it is just very small > > I tried again this morning. On mine the pulse is there but it's very weak. > I can't see it one the scope but I can see the trigger light flash every > second if I work to set it "just right". I also see an about 0.3V peak to > peak, about 60MHz sine wave. I can get the scope to trigger and display > the sine wave just fine. I have to use a 10X scope probe or I load the > signal to "millivolts" > > The PPS signal coming from my Oncore GPS is easy to see on my scope and > even on a DMM set to "DC Volts" > > The FE-5680's PPS is not usable directly with my counter, I have to amplify > it then set the counter to 10X attenuation then mess with the trigger > setting so it does not see the 60MHz signal. Maybe I'm lucky that my > scope has a BNC output on the back for the vertical amplifier, so I can > apply a 20MHz low pass filter and about 20X voltage gain. > > The documentation I have says pin 6 is "N/C" but it looks like there is a > way to extract a usable PPS but I think I'm going to need and LC filter, > some op amps and a one-shot and a TTL level driver. My guess is that pin > 6 is either some kind of engineering test/diagnostic signal not intended to > use used or the signal is an accident > > > > > > > > > -------Original Message------- > > > From: David <davidwh...@gmail.com> > > > To: Discussion of precise time and frequency measurement < > > time-nuts@febo.com> > > > Subject: Re: [time-nuts] FE-5680A performance > > > Sent: 05 Jan '12 07:49 > > > > > > On Thu, 05 Jan 2012 01:44:13 -0800, Hal Murray > > > <hmur...@megapathdsl.net> wrote: > > > > > > >albertson.ch...@gmail.com said: > > > >> > > > >> Have an older Tek 465 scope that is in only "fair" shape and I see > > nothing > > > >> on that pin but milivolt level sine wave of about 60MHz. I can't > > set the > > > >> scope to show any hint of a PPS ... > > > > > > > >I do have a 465. You should be able to see a 1 uSec PPS. > > > > > > 60MHz is about a 6nS rise time and is easily fast enough to see it. > > > > > > >Now turn up the Intensity until you can see the pulse. It might help > > to turn > > > >down the room lights. > > > > > > This is the problem. With a 1 second repetition rate, the brightness > > > is going to be very low. > > > > > > The old ways of viewing such a low repetition rate signal include > > > using a hood or dark room, special CRT phosphors, photographic film, > > > MCP (micro channel plate) intensified CRTs, and of course analog > > > storage and later digital storage. > > > > > > _______________________________________________ > > > time-nuts mailing list -- time-nuts@febo.com > > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.