Short Wave Sportfishing wrote in
:

On Tue, 25 Sep 2007 20:12:48 +0000, Larry wrote:

John H. wrote in
m:

Another question: Most antennae seem to come with about 20 feet of
wire. Mounted on a console with the radio right there, I could get
by with about 3 feet of wire. Is all the extra wire necessary?

No, it's not. If you're not a solderer, find someone who can put a
new connector on the radio end of your cable or make up a new cable.
The Metz does NOT have a cable attached to it....one of its great
features. YOU put the cable on it so the cable can be replaced....not
hard wired into the plastic, like the little whips from Shakespeare
come.

The farce of "tuning" the antenna with cable length is nonsense....

Really.

Tell me why.


No problem.....

Anywhere along the length of a transmission line terminated in its
characteristic impedance (the antennas and cable are 52 ohms), the
voltage and current are constant and there are no standing waves. In
reality, this is not possible, but it is very close.

The old CB nonsense was to use the transmission line's standing waves to
find a place where the impedance is close to 52 ohms. Unfortunately,
this changes with frequency and whatever is wrong with the antenna on the
other end. We hams have used tuned open wire feeders for 90 years or so.
But, none of these antenna systems and transmitters are designed to be
used with tuned feeders, which present the transmitter with a very odd
voltage to current phase relationship that may cause destruction of the
output amp stage.

If the VHF power amp brick detects the wrong impedance or phase, it turns
the power down to protect the brick....never a good thing.

So, in a tuned antenna system, it matters not where you place the
transmitter because the impedance load at any point on the transmission
line is very close to constant.

Larry
--
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The ultimate dirty bomb......