Re: Finding a minor Votage drop on a 50V source... It is possible?


"nina.p20" <nina.p20@xxxxxxxxx> wrote in message
news:1131233200.059984.175280@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Thanks for answering,
> I'm trying to detect a voltage drop on a Telephone line when a 10MOhm
> load is placed across (parallel) the line. I've measured the Voltage of
> line before and after the "load", with a Fluke 197 and found it was
> about 10uV. It interests me very much if using a precision high
> impedance comparator may detect this drop. Any other ideas will be
> welcome of course :)

I would "whack" the line with a decent pulse, up to maybe 200 volts, for a
few microseconds and see what comes back in the form of reflections on an
oscilloscope.

The reflections should match the physical layout of the line, there should
be one where the line is terminated in the junction box f.ex. - a listening
device might show up because one triggers the over-voltage protection on it.

If the tap is magnetic, it might not show up. If it is government, it is via
the "lawful interception interface" built into the exchange and you are
screwed anyway.

Look up "time domain reflectometry" in Google.


.

Quantcast