Ian White GM3SEK wrote:
Richard Harrison wrote:
The Bird wattmeter uses a directional coupler, works as
advertised, and may be inserted anywhere in a 50-ohm coax line.

Sorry, Richard, but that isn't a constructed argument any more. It's
just a declaration.

Do we need to go into the wave reflection model in detail? The Bird
wattmeter accepts the wave reflection model as scientific fact as do
most of my reference books. Given the wave reflection model and a 50
ohm environment, the Bird wattmeter reads forward and reflected power,
i.e. the number of joules passing a point on the 50 ohm transmission
line in each direction. The Bird wattmeter assumes: Forward V is in
phase with forward I. Reflected V is in phase with reflected I.
Vfor*Ifor = Pfor Vref*Iref = Pref
Vfor/Ifor = 50 ohms, Vref/Iref = 50 ohms.
Vfor^2/50 = forward power, Vref^2/50 = reflected power
Ifor^2*50 = forward power, Iref^2*50 = reflected power
All this is in any good textbook covering the wave reflection model
and has been accepted as fact by RF engineers for the better part
of a century.
--
73, Cecil http://www.qsl.net/w5dxp


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