RE: [TCML] Experiment to measure effects of RF grounding

["S&JY" <youngs@xxxxxxxxx>]

Gary,

Probably your shorted scope probe is acting like a 1 turn pickup coil, being
coupled to the TC primary or its associated wiring.  You might have to make
a current transformer with a ferrite donut core.  Make a primary with a few
turns of heavy wire in series with the hot mains line, and a secondary of
another couple of turns fed many feet away via twisted pair to your scope.
Hopefully, this would give you a flat line display when the primary is
shorted and would show the hash when not shorted.  Probably you would have
to orient the core for least coupling with your TC. It might help to add a
power filter in the power going to your scope.

Perhaps measuring power hash at the mains end of a 50 foot power cord to
your coil would provide the decoupling you need.

Or, you could do what Terry Fritz did and use fiber optic isolation of your
scope.

--Steve Y.

> Lau, Gary wrote:
> > Well, having just tried it, maybe there is some element of rocket
science involved
> in scoping mains hash.  I have a fancy Tektronix TDS-series digital scope,
and a
> variety of Tek probes.  Even with the shortest probe, with no wires
connected to the
> tip of the probe, and the probe ground clip tied just to the tip of the
probe, just
> running my coil near the scope or probe provides a nice display of the
bang events
> rather than a flat line.  Unless I can get a scope probe to accurately
read zero with
> the input shorted, it would be futile to try to measure line hash.
Comments and
> suggestions welcome!
> >
> > I still plan to document any correlation in streamer length to various
grounding
> schemes, but I was hoping to do the hash measurements at the same time.
> >
> > Regards, Gary Lau
> > MA, USA
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