Keith Dysart wrote:
On Dec 24, 11:50 am, "Yuri Blanarovich" wrote:
Why is the Bird wattmeter
calibrated in Watts, measuring power (forward and reverse) and has chart to
calculate SWR, when there are no standing waves and no power in them?

Why indeed? The decision of Bird Electronic to build
an instrument that measured actual line voltage and
current and then compute forward or reverse voltage
but display the result in watts has lead to enormous
confusion about the nature of forward and reverse
waves.

If only they had decided to display forward or
reverse volts, life would be much better. People
would not have internalized "forward and reverse
power" to such a degree.

On the other hand, it would have then required
more arithmetic to compute actual power.

But they did it, and it can not be undone.

Do you have an unambiguous definition of "standing
wave power" that can be used?

...Keith

Hi Keith,
When you take the real part of P = VI*, where
I* is the complex conjugate of the current, you're computing
the power in the transmission line. However, the imaginary
part of VI* doesn't disappear, and you should be aware of
its existence if you're going to put a lot of energy into
said line (unless it's a perfect Cecil//Dave line with no
attenuation etc). Yuri is probably arguing from experience
with real lines. Cecil/Dave are arguing from an idealized,
but flawed understanding of the subject. All of them should
go back to school and study the whole elephant, so they won't
keep making the same mistakes the three blind men made.
73,
Tom Donaly, KA6RUH