>"Was it not an FCC requirement to meter the plate current of the final
>amplifier in series with the high voltage and plate of the final amplifier on
>broadcast transmitters? So it was a TRUE reading for plate input power?"
Although possible, I don't recall that as a requirement because AM broadcast
station power in the U.S. is determined by the so-called "direct method." The
direct method of power is determined: (1) directly from measurements of RF
voltage, RF current, and phase; or (2) by calculating the product of the
licensed antenna or common point resistance at the operating frequency and the
square of the unmodulated antenna current as measured at the point where the
resistance has been determined. The latter method is the type most commonly
used.
In a prior life, I recall calibrating our remote antenna current ammeter by
walking out the to the ATU, killing modulation, then breaking the knife switch
across antenna RF ammeter long enough to take a reading and match it to the
remote meter.
The Indirect method of using the more common power formula of P(out) = Ep x Ip
x F is only temporarily allowed when the direct method cannot be used. The
FCC gives some latitude as to the computation used for indirect method
measurements. By contrast, nearly all analog FM broadcast stations measure
power by the indirect method where F (percent efficiency) is determined by the
transmitter manufacturer during testing.
Paul, W9AC
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