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Re: Time Domain Reflectometer (was Re: internet outages)




On Monday 24 December 2018 04:26:05 Joe wrote:

> On Sun, 23 Dec 2018 22:54:20 -0600
>
> John Hasler <jhasler@xxxxxxxxxxx> wrote:
> > rhkramer writes:
> > > Yeah, but I wasn't thinking about actually using a CRT to display
> > > the signal in real time, but, instead, collect samples (at maybe 4
> > > GHz??), store them, and then display them as a static display.
> >
> > At that sort of frequency sampling scopes (including the old crt
> > ones) sample at far below the signal repitition rate.
>
> Yes, they rely on the signal being repetitive. To see a single
> transient, you want at least five samples in the relevant period,
> preferably more.
>
> There is normally a real Nyquist bandwidth quoted somewhere in the
> small print. I used to repair and calibrate Hitachi scopes for a
> while, until everyone stopped using them.

I wonder why, Joe. My V-1065 still works well enough to measure frequency 
at a 1% accuracy, and its now pushing 35yo. In a pinch I've looked at 
the output sample of an old analogue tv transmitter to adjust the 
modulation depth when the monitor was bonkers, it was actually usable at 
180 mhz. 

Their absolute top of the line V-1085, 200 mhz had a totally duff 
triggering circuit in it so I sent 2 of it back, but its baby brother, a 
4 trace 100 mhz was an absolute doll, and the only analogue scope that 
would let you do the final calibration after replacing the head wheel on 
a Panasonic DVC-PRO broadcast vtr. At $1500-2000+ a copy, I've done that 
about 100,000 dollars worth of that. That and replaceing the tiny 
electrolytic caps by the 3 lb coffee can full. 3 of those IIRC before I 
retired in 2002. Failure rate on those in the dvc-pro's was near 100% in 
2 or 3 years. Had to buy 'em from Pan., because all the others were 
physically too big. Glad those are now history and I've retired, bending 
over to see thru a big magnifying light 6-7 hours a day for a week or 
more at a time is half of whats wrong with my back today.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
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-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>