On Sun, 03 Oct 2004 06:54:50 -0700, Bill Turner
wrote:

On Sun, 03 Oct 2004 03:29:17 GMT, Gary Schafer
wrote:

The definition of peak envelope power (PEP) is: "The average power
contained in one RF cycle at the crest of the modulation envelope".
(note that the definition says "AVERAGE power" not RMS power) This is
from the FCC definition.

_________________________________________________ ________

Right you are, but I'd like to know where the definition of average
power comes from. Is it the IEEE?

If the formal definition says VRMS x IRMS = average power, I suppose I
could live with that, but until then, I think it equals RMS power.

Sources, please.


Rms voltage and current are also called "the effective values".

If you have heard that average power is 1/2 of peak power we could
investigate why.

The rms voltage and rms current of a sine wave are found by
multiplying peak voltage by .707. Same for current.
If you multiply .707 by .707 that gives you .5 or 1/2.

1 volt peak Ac voltage times 1 volt peak / 1 ohm = 1 watt peak power.

1 volt peak times .707 = .707 rms volts. .707 rms volts times .707 rms
volts = .5 / 1 ohm = .5 watts average power.


"It takes twice the Ac peak power to provide the same amount of heat
as it does average DC power." Therefore 1/2 the peak Ac power is equal
to it's average power.

Note that rms voltage is defined as the amount of Ac voltage that will
cause the same amount of heating in a resistor as an amount of DC
voltage.


Also note that when describing rms voltage and its heating effects,
that it does not say amount of power required to do the same amount of
heating. It says the amount of rms voltage to do the same amount of
heating in a resistor. (thus, effective voltage) This is where many
get confused.

If you want to know the amount of power you must square the voltage
and divide by the resistance.
There is that .707 x .707 = .5 again for Ac power. (E squared /R)

2000 ARRL handbook 6.6 chapter 6, RMS VOLTAGES AND CURRENTS.

73
Gary K4FMX