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

[John Hasler <jhasler@newsguy.com>]

Gene writes:
> In a cnc machine running on stepper motors, the current regulating of
> the drivers if the grounding is not truly single point, can crosstalk
> at the regulating frequency, usually well above 20 kilohertz, at peak
> voltages well over what it takes to destroy an fpga gate as the
> ringing in that event often peaks at over 100 MHz and 30
> volts. Trivial to see on the samplers display, but turn off the room
> lights and really study what you see on a 100+ megahertz analogue
> scope.

For that sort of thing you want a storage scope.  Old Nicolets are
readily available for prices that even I can almost justify.

I used Tektronix analog storage scopes when doing motor control design
in the seventies but the digital ones are orders of magnitude better.
Being able to trigger on things that already happened is cool.

Before that it was cameras.

As to TDRs, if you can get by without actually seeing pictures of all
the impedence bumps you can get by with a fast counter, a high risetime
pulse generator, and a couple of fast comparators.  Maybe $20 at
Digikey.
-- 
John Hasler 
jhasler@newsguy.com
Elmwood, WI USA