On a sunny day (17 Oct 2005 10:51:15 -0700) it happened "Dungeon Master"
wrote in
.com:

Jon,
When checking a coax with an ohm meter. With the coax disconnected on
both ends, measure from shield to ground. This must be an infinity
reading. Now measure the center conductor end to end. This shouldn't be
over a couple ohms at the most. The same for the shield measurement. If
you have a dummy load, connect it to one end and you should read around
52 ohms with the meter. It's best to do that from both ends to ensure
the connectors are good. The only way better to test is with either a
megger or a TDR time Domain Reflectometer.
If you have you atenna connected, you'll find that with most fiberglass
base antennas, you'll have a reading from 40 - 150 ohms do to the
tuning curcuit inside the antenna.
I hope this helps a little.....
73 de Dungeon Master
Small correction:
There is a difference between 'rsistance' and 'impedance'.
For example when I measure the 'resistance' (with the Ohm meter) from
my 1/2 wave GPA, I measure a dead short.
This is because there is a little transformer in it, you measure the Ohms
of the wire in the primary.
the *impedance* however is around 50 Ohms (I would hope).

There is a simple way to measure impedance too, in a bridge:
http://web.telia.com/~u85920178/antennas/bridge.htm

The reason is that for DC a transformer is almost dead short....