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




On Sunday, December 23, 2018 09:03:15 PM Gene Heskett wrote:
> On Sunday 23 December 2018 20:27:37 rhkramer@xxxxxxxxx wrote:
> > On Sunday, December 23, 2018 07:33:38 PM Doug wrote:
> > > RE: Time Domain Reflectometer:
> > > 
> > > Theoretically, you can build your own with a fast pulse generator
> > > and an oscilloscope. The trick is, you need a REALLY FAST
> > > oscilloscope!  The pulse generator is easy, just a couple of
> > > transistors, maybe a diode. The  circuit is probably in every
> > > edition of the Radio Amateur's Handbook. The scope is expensive. If
> > > you don't have at least a 1GHz digital sampling scope, don't bother!
> > > 
> > > --doug, WA2SAY, retired RF engineer
> > 
> > Hmm, with CPU clocks hitting 4 GHz, I wonder how expensive an ADC
> > converter to work at corresponding speeds would be?  (Just an idle
> > question ;-)
> 
> If you have to ask, you can't afford it. Bring outrageous sums of money
> This is typically done by every trick tek knows about fast analogue
> circuitry, in the best units with long vertical deflection plates in a
> custom made crt with teeny delay lines between the sections of the
> plates so the signal is virtually traveling toward the screen at the
> same speed as the electron beam is traveling. And its moving fast enough
> at 22,000 volts, relativity can and does get in the way. Such scopes put
> the plates so close to the beam that the beam is intercepted by striking
> the plates at just a hair over 4 cm high, 2cm from the horizontal center
> line. The only one of those I ever saw was in the early 1980's or so at
> the NAB show in Vegas, and it was well into a 5 digit asking price then.

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.

???