Yuri is somehow trying to mix in an antenna that has more
bandwidth because the conductors are thicker and more lossy,
with a discussion about feedlines.
In this case, we are talking only about the feedline length. Not
changing the actual antenna. Let's not make attempts to confuse
people by changing the antenna element from a thin wire to lossy
thick coax and say that has something to do with the feedline
length!!
> I don't think it is absolutely true that line loss is the only
> mechanism that can increase system bandwidth. If the reactance change
> of the mismatched line happens to work in opposition the reactance
> change of the load, then then a lossless cable could in principle
> increase system bandwidth.
Some time spent with a Smith Chart will dispel that idea Mike.
It is **VERY** well established the SWR of a transmission line
connected to any load is independent of length except for a change
caused by loss in the line.
The only exception, other than SWR improvement through
additional loss, is when the transmission line is part of the radiating
system.
This certainly works when a series resonant
> circuit of proper loaded Q is placed in front of a load with with an
> opposing reactance change versus frequency. Unfortuntately, the
> direction and or rate of the reactance change is usually wrong, so
> this technique only works in specific cases.
What is the resonant frequency and Q of a terminated transmission
line Mike?
We are talking about a transmission line feeding a load, not an
additional shunting resonant stub.
Seriously, all the stuff about a transmission line acting like two
series resonant circuits and such is wild arm waving without an
ounce of truth. The SWR along any length of constant impedance
transmission line is constant for a given load impedance, except for
any SWR change caused by losses in the line.
Now there are exceptions if the line is part of the radiating system
(which would be a bad idea with a beam antenna) or if you or your
instruments are measuring SWR incorrectly, but any SWR
improvements in a transmission line with length are only caused by
addition of loss.
73, Tom W8JI
W8JI@contesting.com
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