What PEP means
Peak envelope power is the average power over one RF cycle at the highest point of the signal's envelope. For a constant carrier, such as CW, FM or FT8, PEP equals the average power. For SSB voice, the envelope rises and falls with speech, so the average power is much lower, typically 10 to 20% of PEP without speech processing. UK, US and Australian licence power limits are given as PEP.
Measuring with an oscilloscope
Connect the transmitter to a dummy load and look at the RF across it through a suitable attenuator or high-voltage probe. Read the peak-to-peak voltage at the top of the envelope. PEP is then (Vpp ÷ 2 ÷ √2)² ÷ R. 100 W into 50 Ω is about 200 V peak to peak, so make sure the scope and probe are rated for it.
Why it matters
- Components such as baluns, ununs and filters must handle the peak voltage and the average power for your mode. A 100 W FT8 signal heats them far more than 100 W PEP of SSB.
- The dBm and ERP calculator converts power to dBm and works out ERP.
- The EMF calculator uses average power, which depends on mode.
Questions
What does PEP mean?
Peak envelope power: the average power over one RF cycle at the peak of the modulation envelope.
What voltage is 100 W into 50 Ω?
About 70.7 V RMS, 100 V peak and 200 V peak to peak.
How much average power is SSB?
Typically 10 to 20% of PEP for normal speech, and 30 to 50% with heavy compression.
Are licence limits in PEP?
Yes, in the UK, the US and Australia, power limits are given as peak envelope power.