AMERITRON AL-80B, Инструкция по эксплуатации

Страница: 11 / 38

AL-80B Instruction Manual
7
Wattmeter Circuit
The AL-80B wattmeter circuit uses an accurate directional coupler followed by a true peak detector
circuit. This circuit will accurately determine the true peak envelope power (PEP) of normal voice
waveforms. If the load SWR is high, the true power reading will be obtained by subtracting the
reflected power from the forward power.
Peak Envelope Power vs. Average Power
Peak envelope power (PEP) is often misunderstood by amateurs. PEP
is not associated with the
sine wave or root-mean-square (RMS) power, and PEP has no fixed ratio to average power on any
mode except FM, FSK or CW. It is impossible to use a formula or "rule of thumb" approximation to
convert between average and peak voice waveform powers.
PEP is the power at the crest (highest point) of the RF envelope waveform. On SSB, the average
power can vary from a few percent of the PEP to over half of the PEP. Generally, the PEP on SSB
is two to five times greater than the average power. A 50 watt average power SSB signal could have
peak envelope powers that are lower than 100 watts or that exceed 250 watts.
On CW and other constant amplitude modes (such as FM or RTTY), the PEP is
always equal to the
average power. On CW, FM or RTTY 1000 watts of average power produces exactly 1000 watts of
PEP.