I'll keep this simple.

I have a mobile radio mounted in my car. It's an Icom 207H 2m Mobile. I
need to somehow (as easily, cheaply, and quickly reversible as
possible) restrict the transmit distance to something quite short (say,
between 50 and 200 feet, at the maximum). What's the best and easiest
way to do this, while still keeping something that can be easily
reversed?

Disconnect radio from antenna.

Connect radio to good-quality VHF-rated dummy load.

Will simply running the radio on low power (5W) with no antenna do the
trick, keeping in mind that the radio is inside a metal car?

It will quite possibly damage the radio's RF finals. Some radios have
good high-SWR protection, others do not. How lucky to you feel today?

Use a dummy load, and minimum transmit power. Enough RF will leak out
of the radio and coax to allow you to hear it tolerably well over
short distances, and it should pick up enough of whatever signal you
transmit from an HT to be able to receive well enough.

Or should
I somehow shield the end of the coax and/or the body of the radio?

*terminate* the end of the coax with a 50-ohm dummy load.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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