> How can a tuner at the tx end change the impedance mismatch between the
> feedline and the antenna into a match?
> Did you mean to say " a mismatch between the end of the feedline and the
Perhaps I should have said that it establishes a 'conjugate match' to avoid
confusion.. In a system such as rig/tuner/line/antenna a conjugate match
established at any point in that system results in a conjugate match at
every other point in the system. A tranmission line acts like a transformer.
If you attach an impedance at one end, a certain impedance will appear at
the other end. It's magnitude depends on the line length, characteristic
impedance of the line, frequency, and the impedance attached at one end.
Thus, by changing the impedance at one end, you can effectively change the
impedance at the far end. Conjugate matching is required for maximum power
transfer and that is what a tuner does. It's adjusts the far end impedance
so that maximum power gets transferred from the line to the antenna
regardless of the impedances of either.
So, regardless of the impedance values of the line and antenna, the use of a
tuner at either end establishes the required conjugate matching condition
for maximum power transfer and thus maximum radiation. If your rig pumps 100
watts, 100 watts gets radiated less the amount of power lost in the line due
to its inherent loss and loss due to a finite swr. Putting the tuner at the
antenna eliminates line loss due to a finite swr. It's the ideal place to
put it but, as Jerry pointed out, it has certain undesireable disadvantages,
namely, its hard to get at it.
Putting the tuner at the rig end results in line loss due to a finite swr
but there is no loss due to an impedance mismatch at the line/antenna
junction! If the loss due to swr is unacceptable, the only thing you can do
is use a shorter or a lower loss line.
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