On Mon, 08 Dec 2008 12:32:14 -0500, "Michael A. Terrell"
wrote:


mm wrote:

On Fri, 05 Dec 2008 15:07:46 GMT, "TKM" wrote:


Who knows if it's OK to measure the resistance (using a standard multimeter)
of a coax line connected to an amplified antenna after disconnecting the
amplifier power supply, but not the antenna. I'm concerned about damaging
the amplifier inside the antenna,

You want to measure the resistance of the center conductor, right?

Easy to connect to the coax, but what do you want to connect to at the
other end? The rods that stick out of the antenna?

The voltage from a multimeter, 9 volts usually, isn't going to hurt
anything, but I don't think you can expect a meaningful measurement
either.


What kind of meter are you using with 9 V between the probes?

Well it's been decades since I measured the voltage, if I ever did, so
let me just say that the voltage will be NO MORE THAN the 9 volt
battery provides. It might be less, but there are no voltage raising
circuits in a "standard multimeter", which the OP plans to use.

Ohm
meters are usually current limited, or constant current sdesigns.

How would knowing this help him? His concern was about damaging his
amplified antenna.


There are semiconductors between the input and output of the
amplifier, and with no power, they might be acting as non-conductors.
Maybe I'm wrong about that, but how would you know if the resistance
is good or not, short of finding an identical antenna and measuring
it?

but suspect an open line going from the
lightning arrestor up the roof to the antenna.

So can't you disconnnect the cable at the antenna and measure the
resistance through the line with the arrestor only?

TKM