On Mon, 30 May 2005 16:12:44 -0500, Cecil Moore
wrote:

Fred W4JLE wrote:
Assuming I have an antenna that is perfect on 3.8 MHz. Perfect being
defined, as I am feeding it with exactly 1/2 electrical wave length of 50
Ohm feedline and it is 1:1 SWR measured at the source end.

What would the SWR be if I substituted the 50 Ohm feedline with a 1/2
wavelength of 72 Ohm feedline?

The SWR on the 72 ohm feedline would measure 1.44:1. You do
have an SWR meter calibrated for 72 ohms, don't you? :-)
Your 50 ohm SWR meter will measure 1:1, but as Reg says,
it is merely measuring the degree of match to your
transmitter designed for 50 ohm loads.


Gentlemen, I know most of you are much more knowledgeable in some of
this, but with all your nit-picking over the impedances, etc., may I
interject that something is being overlooked?

The antenna feedline has some loss, however little, that may affect
the swr at the "source", which I interpret to be at the radio.

100 watts may be transmitted, 90 watts received at the antenna, 9
watts reflected, and 8.1 watts received back at the rig for reflected
power. My numbers are hypothetical, but you get the idea.

However, your discussions concerning SWR bridge impedance have led me
to wonder how accurate the swr meter in my rig is concerning the
antennas I use. I feed a dipole with 72 ohm into my rig, an IC-706
MKII which expects a 50 ohm load.

My attitude is that it must be ok if the rig sees it as low as it
should measure it as it sees it.


--
73 for now
Buck
N4PGW