Ian White wrote:

1. The Bird "wattmeter" does not in fact sense power. At the detailed
level, it senses voltages and currents in its internal transmission
line, and then sums and subtracts them to give RF voltages that the
diode detects. I repeat, there is no sensing of power as such, and no
detection of power as such.

My point is that all directional couplers DO work by sensing forward and
reflected waves of voltage and current BUT NOT WAVES OF POWER.

The inner workings of every directional coupler can be explained
*completely* in terms of waves of voltage and current. That includes
resistive bridges, Bruene bridges and parallel-line couplers (of which
the coupler in the Bird is a sub-class). They all work because E and I
waves are phasors, and the construction of the coupler makes them add in
one direction and subtract in the other. There's an example of a
detailed analysis, about the Bruene bridge but applicable in principle
to other types as well, at:
http://www.ifwtech.co.uk/g3sek/in-pr...-of.htm#bruene

Waveguide directional couplers work in very similar ways, but have to be
analysed in terms of forward and reflected E and H fields. That kind of
explanation also works for a waveguide circulator, the difference being
that some of the fields are inside a magnetic medium. A coaxial
circulator is more complex because it involves voltages and currents on
the line part and also E and H fields in the magnetic medium, but the
principle is the same.

This is all standard stuff that has been known for decades. Forward and
reflected waves of V and I (or E and H) give a complete explanation of
the directional properties of all such devices.

Let me turn the question around, Cecil: can you explain in detail how
any directional coupler gets its directional properties, using *only*
your concepts of power waves?

Ian is precisely correct when he says power meters such as the Bird, or
Bruene's Directional Wattmeter DO NOT sense power, they sense only voltage
and current. The meter indicating the power is simply calibrated to indicate
the E^2/Zo power flowing in the characteristic impedance, Zo, of the line.
E^2/Zo = power, and that expression was used to calibrate the meter scale in
terms of the voltage and current propagating in either direction. See Page
3-16 in Reflections 1 and Page 3-15 in Reflections 2, taken from Warren
Bruene's QST article, April 1958, Ref 38 in Reflection.

Walt, W2DU