Richard Harrison wrote:
Ian, G3SEK wrote:
"What are those V`s and I`s doing in your reply?"

Cecil is right on target. Power is VxI. The Bird takes carefully
balanced samples of V&I. In the incident wave the samples are in-phase.
In the reflected wave the samples are 180-degrees out-of-phase. By
exactly balancing the two samples, the reflected wave cancels. Only the
incident wave is sensed. To sense the reflected wave only, the polarity
of one of the two samples is switched.

Correct. I have said that, or near, several times in this and preceding
threads. An article saying the same has been on my web site for almost a
year.

I am now more dangerous. Until today, I had never seen one of Kraus`
books. I now own the third edition of "Antennas (for all applications)".
Kraus says there are "fundamental" units and "secondary" units. The
"Ampere" is a fundamental unit. All secondary units can be derived from
the fundamental units.

That is of course true... but if you believe it relevant to this
discussion, you are indeed much more dangerous.

In the Bird, the given is a 50-ohm line. Power is 50(I)(I), since I=E/R
= E/50, and E = 50(I) = V.

Power = EI

The Bird is accurate enough using a sample of E and a sample of I and
scaling to determine power.

As you yourself say, the Bird senses current and voltage samples; and
these are then added (forward) or subtracted (reverse). There is no
physical mechanism inside the Bird by which E x I multiplication takes
place, so power is not directly sensed or measured.

Multiplication is just scaling or the number
of times you repeat a number in an addition column.

That is a kindergarten concept that only works for integers (how do you
repeat a number 3.14159 times?) and anyway, it physically does not
happen inside a Bird.

In the Bird, scaling
is an electrical adjustment.

No, the meter scale comes from an external calibration.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek