James barrett wrote:

Hi, I like the article. One question about feed lines. If coax is 50
ohms and twin lead has 300 ohms. Why is the twin lead consideres less
lossy than coax? I had thought that higher ohms meant higher impedance
and I thought higher impedance means higher loss. Obviously I have not
read the chapter on transmission lines yet ;-), so I may have that all
wrong.

Yes, you do. If a line is terminated in a load equal to its
characteristic impedance, the current along the line is sqrt(P/Z0) where
P is the power and Z0 is the line's characteristic impedance. You can
see from this that for a given power, the current is less if Z0 is
greater. From HF through UHF, the loss in a transmission line is
predominantly due to the resistance of the conductors, resulting in loss
proportional to I^2 * R, where R is the RF resistivity of the conductors
including skin effect. So when you increase Z0, it decreases current,
and therefore decreases loss, all else (such as conductor size and
material) being equal. I used a matched line for simplification, but the
lower loss also holds when the line is mismatched.

Also, in the article, I liked the part about before 1950, no one even
heard about swr, and that antennas with high swr were working just
fine.

The beginning of the hams' fetish with SWR corresponds to the
availability of inexpensive meters to measure it. Once it could easily
be measured, it gained a perceived importance way beyond reality.

But I make 2 assumptions: 1) I'm thinking, even if they didn't
know or care about swr, they still had to cut their dipoles for the
band they were transmitting on.

No, they didn't then and they don't now.

2) I still would not want to use a 10m
dipole and transmit 100 watts on 80 without at least using a tuner. Am
I correct in these assumptions?

Yes, that's correct. One thing that *has* changed between then and now
is that rigs used to incorporate a tuner (pi matching network), so often
an external tuner wasn't necessary. Today's rigs don't have this
built-in impedance matching capability.

Roy Lewallen, W7EL