"Cecil Moore" wrote Reg Edwards wrote:
Where does the inconistency lie ? Does it lie in the change in
effective
source impedance?

It lies in using the wrong coax Z0 for the situation. Assuming it's
long enough to develop 75 ohms, it will cause 4% of the forward power
to be reflected back toward the source at the meter. Guess you can't
call it a TLI after all since it is faithfully reporting the 50 ohm
SWR and not making the transmitter happy. :-)
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Cec, wrong! It is true the very incorrect use of 75-ohm line by the system
designer is the reason for the UNDETECTED deviation from 50 ohms of the Tx
load.

The reason it is undetected is because the SWR meter is in error. Although
the meter indication has not changed since the 50-ohm cable was in situ, it
is now in error because it can measure correctly only on 50-ohm lines but
the actual line being measured is 75-ohms.

So the meter can still be called a TLI. The moral of the story is "If the
connection between transmitter and SWR meter or TLI is of appreciable
length then always use 50-ohm coax."

Good to see you are still taking an interest. ;o)
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Reg, G4FGQ