"True SWR" doesn't change, but *WHERE* it is measured will vary widely.
exception : perfect Z load for perfect Z line where Zload=Zcoax
You are measuring VOLTAGE inside the coaxial line and the voltage
varies along the length of the line like a sine wave.
Some distances from the wrong Z load = peak voltage
Some distances from the wrong Z load = minimum voltage
Some distances make for a close-to-perfect input match.
1/4 wave away from the above perfect match is a point that
your transmitter probably won't like.
In other words, changing the coaxial length *COULD* improve
your situation, but it could also make it worse.
The Smith Chart is your friend, or just make five jumpers of
1,2,4,8,16 feet with a handful of couplers and start substituting
jumpers between the meter and the load. One combination will *MATCH*
or make a length that the transmitter likes. Others will make it
worse.
This is why it's important to measure the Z *AT* the load and not
through an arbitrary length of coax.
Don W4DNR
## On a related note, why is it, when I increase the length of 50
ohm coax from my drake amps to the xcvr, that the
input swr rises ?? Its flat with 4 ft or less.... but rises
when say 5-8 ft is used. Thats on all bands.
<REPLY My understanding is that's a false reading caused by current flowing
on the outside of the coax braid. The true SWR does not change.
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