Peak Envelope Power
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Peak envelope power (PEP) is the average power over a single
radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...
cycle at the crest of the
modulation Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...
. PEP is normally considered the power output at the occasional or continuously repeating crest of the modulation envelope under normal operating conditions. Many regulatory authorities use PEP to set maximum power standards for radio transmitters.


AM PEP

Assuming linear, perfectly symmetrical, 100% modulation of a carrier, PEP output of an AM transmitter is four times its carrier PEP; in other words, a typical modern 100-watt amateur transceiver is usually rated for no more than, and often less than, 25 watts carrier output when operating in AM.R. Dean Straw, ed. ''ARRL Handbook For Radio Amateurs''. Newington, Connecticut: American Radio Relay League, 1999, p. 15.6


PEP vs. average power

PEP is equal to steady carrier power, or
radiotelegraph Wireless telegraphy or radiotelegraphy is the transmission of text messages by radio waves, analogous to electrical telegraphy using electrical cable, cables. Before about 1910, the term ''wireless telegraphy'' was also used for other experimenta ...
dot or dash average power, in a properly-formed CW transmission. PEP is also equal to average power in a steady FM, FSK, or RTTY transmission. Although average power is the same as PEP for complex modulation forms, such as FSK, the peak envelope power bears no particular ratio or mathematical relationship to longer-term average power in distorted envelopes, such as a CW waveform with power overshoot, or with amplitude modulated waveforms, such as SSB or AM voice transmissions. Typical average power of a SSB voice transmission, for example, is 10-20% of PEP. The percentage of longer term average power to PEP increases with processing, and commonly reaches ~50% with extreme speech processing.


PEP level control

Most modern amateur transceivers sample PEP to adjust power, using an ALC (automatic level control) system. Time delay in the ALC system and finite time of RF signals passing through multiple stages, in particular narrow filters, often gives rise to unusual envelope distortion. This distortion commonly appears as envelope power overshoot on leading edges, and sometimes causes negative carrier shift on AM. Some more poorly designed transceivers have a short term envelope power overshoot several times the steady-state PEP setting. This envelope overshoot further complicates definitions of PEP and average power. PEP was often used in non-
broadcast Broadcasting is the data distribution, distribution of sound, audio audiovisual content to dispersed audiences via a electronic medium (communication), mass communications medium, typically one using the electromagnetic spectrum (radio waves), ...
AM applications because it most accurately described the potential of mobile transmitters to interfere with each other. Its use is now somewhat
deprecated Deprecation is the discouragement of use of something human-made, such as a term, feature, design, or practice. Typically something is deprecated because it is claimed to be inferior compared to other options available. Something may be deprec ...
, with the ''average''
transmitter power output In radio transmission, transmitter power output (TPO) is the actual amount of power (in watts) of radio frequency (RF) energy that a transmitter produces at its output. TPO is a concept related to effective radiated power (ERP), but refers t ...
(or sometimes ''average''
effective radiated power Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter. It is the total power in watts that would ha ...
) now typically being preferred.


References


See also

*
Federal Standard 1037C Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms, is a United States Federal Standard issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, ...
{{DEFAULTSORT:Peak Envelope Power Radio transmission power