[Amps] Re: Bird® 43 Manual

[Kim Elmore]

At 11:25 AM 3/28/2002 -0500, you wrote:
> > No.  Watt meters that hams and most engineers use at RF measure either
> > voltage or Current.  They do not measure *power*.  Given the voltage or
> > current, analog meters use a graphical conversion (called a meter scale) to
> > equivalent power given under the assumption of a matched
> > termination.  Digital meters also perform a conversion in firmware.  None
> > of these devices measure *power*.
>
>My example is relevant without the need of the Bird wattmeter.  I fully 
>accept the fact that the directional coupler samples RF
>voltage.  I'll respond to you as I did with Steve.  Namely, in the absence 
>of a load on a loss-less line, any and all reflected
>power is being absorbed by the fixed-impedance source (i.e., broadband PA).
>
>If reflected power is not absorbed by the source, where is absorbed?
>
>-Paul, W9AC


I believe that the logical flaw in the argument lies in discussing 
reflected *power*.  *Power* cannot reflected; only voltage and current are 
reflected.  We speak of reflected power merely as a convenience because the 
meter we're looking at unfortunately has "power" written on it.  In truth, 
it should say "voltage," so that we could more easily talk about what's 
really happening.  Voltage and current presented to a resistive load, 
together and in phase, result in "power."  We speak of "power" being 
transferred down a transmission line, but this power is merely a construct: 
the only things that we can measure on the transmission line are voltage 
and current.

Kim Elmore, N5OP



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                           Kim Elmore, Ph.D.
"All of weather is divided into three parts: Yes, No, and Maybe. The
greatest of these is Maybe" The original Latin appears to be garbled.