Frank wrote:
Did I miss something? As far as the Bird is concerned, all it sees is 50
ohms, indistinguishable from a 50 ohm termination, on its connector.

Exactly the point, Frank. The Bird doesn't know it is embedded
in a 75 ohm environment and reports bogus results because it
assumes it is embedded in a 50 ohm environment, which it is not.
This is Reg's main point in wanting to call the SWR meter a TLI
meter.

The Bird is not to blame for reporting bogus results. It is the
operator who is to blame for using a 50 ohm meter in a 75 ohm
environment and reporting the bogus results as valid.

100w--tuner--75 ohm coax--x--1/2WL 75 ohm coax--50 ohm load

Without a Bird installed at point 'x', most everyone would
agree that the SWR all up and down the 75 ohm coax is 1.5:1
and the voltage and current at point 'x' are the same as the
in-phase voltage and current at the 50 ohm load.

The voltage at point 'x' is 70.7 volts, and the current at point
'x' is 1.414 amps. The SWR on the line is 1.5:1.

Now, installing the Bird at point 'x' doesn't change anything
appreciably. The voltage at point 'x' is still very close to
70.7 volts and the current at point 'x' is still very clost
to 1.414 amps. Those two parameters are what the Bird samples
and all the Bird sampoles. And since the Bird is calibrated for
50 ohms, it reports a bogus SWR of 1:1. If the Bird is recalibrated
for 75 ohms, it will report the correct SWR of 1.5:1.
--
73, Cecil http://www.qsl.net/w5dxp