RadioBanter - View Single Post

February 2nd 07, 05:27 AM posted to rec.radio.amateur.antenna

Cecil Moore wrote:

wrote:
maybe I should have asked does my coax tune my antenna???????

When the load impedance is not 50 ohms and the
target impedance is 50 ohms, 50 ohm coax cannot
tune your antenna system to a 50 ohm match. In fact,
using 50 ohm coax with an SWR not equal to 1:1 is
one way of guaranteeing that the transmitter will
*never* see 50 ohms without some help from a
tuner or other matching method. (Extensive losses
will also bring the SWR closer to 1:1).

If the target impedance is 50 ohms, only a
characteristic impedance different from 50 ohms
can transform the non-50 ohm impedance to 50
ohms. And that can only be done when the SWR is
not 1:1. Note that in Owen's 1/4WL matching
equation, only if the load and source are both 50
ohms does the equation result in Z0 = 50 ohms.
Such a system is called a "flat" system with a
trivial default SWR of 1:1.

An autotuner at the feedpoint will solve the
problem or a parallel feedline with a Z0 of
300-600 ohms will solve the problem. I have
solved the problem at my QTH with a 148 foot
dipole and 90 feet of 450 ohm ladder-line.
That antenna system is simultaneously resonant
at my QTH on both 7.15 MHz and 3.8 MHz at the
same time. And it is also close to resonance on
17m.

can this be done with one feedline?

--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!