>
> The standing wave ratio is the standing wave ratio and it refers only
> to the match between any transmission line impedance and it's load's
> impedance. (never anything else)
Almost never anything else. Example: 100 ft of line comprised of two or more
sections whose characteristic Z are different.
Let's say half the line is a Zo=50 and the other half is 70. The SWR is
different along the line. It's one value for the 50-ohm section and a different
value on the the 70 section.
Getting back to the original issue, I'm intrigued as to why some amp
manufacturers specify a length of line between the transmitter and amp.
As others have pointed out, SWR should remain constant when the load Z is
constant -- as long as there no current flow on the outside of the outer
conductor. Any mismatch at the amp input results in a Z change in a circle
around the Smith Chart as also previously mentioned. But our amps are used on
many bands so what's the mathematical computation to get to a specific length
of interconnect cable when there no wavelength association?
In the case of the 30L-1, I had read that Collins specified a length that was
used to stabilize the amp on one band. In essence the interconnect cable
becomes a line stretcher to move the complex Z to stable point on the Smith
Chart.
For highly swamped, resistive amp inputs, SWR between the transmitter and amp
should see little change with amp class over the RF cycle. This is the case
with the tetrode based ACOM 2000A. I had thought the Alpha 8410 had a similar
swamped input structure.
Paul, W9AC
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