[time-nuts] Scopes and 1 PPS signals?

Didier Juges didier at cox.net
Tue Oct 23 23:47:17 EDT 2007

Digital camera (Samsung D53, 5Mpx, 3x optical zoom, 2.4" LCD, was $88 at
WalMart last year) on a bipod, my arms :-)
Flash is turned off, scope contrast adjusted for normal use.

I have the Comm module for the TDS-210, and I have the GPIB controller and
John Miles' software, which I use with the spectrum analyzer. But, my main
computer is not very close to the lab bench, and the laptop is in another
room at the moment, so it's just easier to take the digital camera. 

I bought my TDS-210 at a local hamfest a few years ago and I never regretted
it. It's a great little instrument.

I only have a couple of gripes with it: 1) the contrast voltage is not
temperature compensated, so you have to adjust it when you turn the scope
on, then a couple more times during the first few dozen minutes of
operation, then it will stay good forever, not a biggie.

2) the trigger point wants to be at the center of the screen, and if it's
not, it's going to be so many mS or uS from the center of the screen when
you adjust it for instance. From that point, if you change the time base,
the trigger point moves to remain at the same time delay from the center of
the screen. You can very rapidly have the trigger point a mile or so to the
left of the screen, so to speak, and that can be aggravating when you turn
the horizontal control knob to bring it back into the screen :-) I'm still
not used to it after many years. I wish we could set the scope to have the
trigger point at one or nine divisions, and it would not move when you
change the time base, like the old 468.

These are nothing major, the scope is great.

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 10:20 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Scopes and 1 PPS signals?
> Hi Dider:
> I'll give that a try tomorrow.  What does your camera setup look like?
> Digital SLR on tripod?  Does that mean the TDS-210 can not do 
> a screen dump to file?
> I've been looking at the Rigol DS1102CD mixed signal scope.  
> The 100 MHz 2 analog channel & 16 digital channels is very 
> reasonably priced.  But after 3 emails I still have not been 
> able to see a programming manual for it.  Although they do 
> have a software package.
> 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:
> > ); SAEximRunCond expanded to false
> > Errors-To: time-nuts-bounces+brooke=pacific.net 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 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
> > 
> > 
> > 
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