Peak Envelope Power
The FCC defines Peak Envelope Power for radio amateurs as, "The average power supplied to the antenna transmission line by a transmitter during one RF cycle at the crest of the modulation envelope taken under normal operating conditions." [47CFR97.3(b)(9)]
The International Telecommunications Union defines it in the same way. [RR1.157]
That definition is confusing, at best. Hopefully, this page will clarify its meaning.
RF signals such as AM and SSB have a constantly changing amplitude during transmission, like the image at the top of the page. For these signals, there will be points where the amplitude is at its greatest (see Figure 1). This is the "one RF cycle at the crest of the modulation envelope" in the definition. Other signals, such as FM, PM (phase modulation) and CW, have a constant amplitude, so every RF cycle is its "peak" cycle.
Figure 1. Peak Envelope Voltage
Once that cycle is identified, we calculate the average power over its complete duration. That's the red area in Figure 2.
Note that we calculate the power in both the positive voltage halfcycle and the negative voltage halfcycle. They don't cancel out because, as shown below, the PEV is squared, making both of them positive. Figure 2. Peak Envelope Power Sine Wave
Start by measuring the amplitude of the peak, usually in volts. That is PEV in Figure 1.
Then apply the following formula:
Where:
* PEP is Peak Envelope Power, in watts
* PEV is Peak Envelope Voltage, in volts
* R is resistance, in ohms
In most amateur radio systems, R is approximately 50 ohms.
The part of the formula in the parentheses (PEV x 0.707) converts the PEV to volts_{RMS}.
This reduces the formula to the familiar Ohms Law for power:
An example:
If the PEV = 100 volts with a 50 ohm load, then:
(Image sources: ARRL and de.wikipedia.org)
