[AMPS] Watt meters and PEP

[Ian White, G3SEK]

Terry Gaiser - W6RU wrote:
>
>§97.3 Definitions.
>(b) The definitions of technical symbols used in this Part are:
>
>(6) PEP (peak envelope power). 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.
>
>----------------------------------------------------------------------------
>----
>
>To me the above FCC specification is missleading ..... I agree with
>everything EXCEPT ... "The average power" ..... the average power supplied
>to the antenna can vary all over the place with a peak value of 1500 watts
>at the crest af the modulation cycle !

The FCC definition is exactly correct. It is the "average power supplied
during one RF cycle". That is the definition of "power" in any AC/RF
waveform.

Two things are varying on very different timescales. 

The instantaneous RF power is varying from moment to moment within the
RF cycle, but that is of no practical relevance. Engineers never
calculate instantaneous power (except by mistake). They only calculate
the average over a complete RF cycle, and that's what they define
"power" to be.

On a much slower timescale, whole RF cycles are varying in amplitude due
to the modulation. The "peak" in "PEP" means the peak of the modulation.
The drawings on Lu's web page show this very clearly.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek

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