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




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.

Cheers, Gene Heskett
-- 
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