[time-nuts] FE-5680A performance - 1 PPS output issue

[Azelio Boriani]

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.chris at gmail.com>wrote:

> On Thu, Jan 5, 2012 at 9:46 AM, beale <beale at 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 <davidwhess at gmail.com>
> > >  To: Discussion of precise time and frequency measurement <
> > time-nuts at 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
> > >  <hmurray at megapathdsl.net> wrote:
> > >
> > >  >albertson.chris at 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.
> > >
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> >
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>
>
> --
>
> Chris Albertson
> Redondo Beach, California
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