Ian White GM3SEK wrote:
Richard Harrison wrote:
To determine reverse power flow, the polarity of one of the samples is
reversed.

And here you've made that big leap again. Where did "power" come from?
Nothing in what you or I have said above explains how come the meter can
read "Watts".

Bird assumes the meter is being used in a 50 ohm environment. Bird
assumes after the two sample voltages are superposed, that the
calibration is accurate to within 5% of full scale. The calibration is
done using 50 ohm matched lines.

In a transmission line, the net power transfer is V*I*cos(theta). It
can be proven mathematically that, for a transmission line with
reflections,

Pnet = V*I*cos(theta) = Vfor*Ifor - Vref*Iref

The Bird sampling circuit allows one to read either (Vfor*Ifor) or
(Vref*Iref) by turning the slug. Bird assumes Vfor/Ifor = Vref/Iref =
50 ohms.
--
73, Cecil http://www.qsl.net/w5dxp