I am glad I chose to display my ignorance, I have learned a lot.

I will modify my earlier position that High SWR causes TVI to Roy's
better explanation that they seem to have the same causes.

I have noted that other people seem to get along with High SWR's and
Non resonant antennas. Neither has worked well for me in the past.

I used to operate ATV on 440mhz with a 48 element collinear antenna.
(I did not do the initial construction) It was basically a collection
of dipoles and reflectors tied together with open wire phasing
harnesses. I could never quite figure out what the harness might be
losing. The antenna seemed to be worth about 21db with very primitive
measuring schemes. I speculated that it had a theoretical potential of
48db. I always felt that the phasing harness was the major contributor
to the losses.

With each driven element being resonant, some measure of success was
assured with each one. At 440, feed line losses get critical in a
hurry.

The transmitter final was a military surplus cavity with a 4CX250 that
had been "stuffed" to get it up to 440. As a side effect the output Z
was determined to be pretty low by trying several home brew quarter
wave coaxial matching sections. When a good match was made, a lot of
problems went away. Not only was I managing a better signal, but the
polyethylene cooling ducting was taking a longer time to melt down.

Hence, my position that SWR IS important.

Please note: I am not here to pick an argument, I recently took
W4RNL's antenna course, bought Roy's EZNEC+ program, downloaded (still
studying) Reg's many programs and have taken note that Cecil is a
motorcycle fan like my Dad was.

When I provoke an argument, I am trying to learn something.
BTW, I do have a pretty good library of reference books but you guys
explain it better in terms I can grasp!


On Wed, 21 Dec 2005 22:45:20 -0800, Roy Lewallen
wrote:

John Ferrell wrote:

Here is the short version:
A matched transmission line behaves like the theory books say it does.
The rated power from the transmitter goes through the transmission
line with the lowest possible loss to the antenna where it is radiated
just like the book says.

Mismatched transmission lines also behave like the theory books say. The
rated power from the transmitter goes through the transmission line to
the antenna where it is radiated just like the book says.

I deleted only "with the lowest possible loss" because increased SWR
does increase line loss. But if the line loss is low when matched, the
increased loss due to high SWR is often negligible.

. . .

Roy Lewallen, W7EL
John Ferrell W8CCW