[AMPS] Watt meters and PEP

[Dave D'Epagnier]

Hey Ian, what do you make of all these audio amplifier manufacturers
specifying their equipment output power to be in rms Watts? This doesn't
make sense to me. I always thought Watts was average power and that RMS
Watts was meaningless.

--Dave
K0QE

	----------
	From:  Ian White, G3SEK [SMTP:G3SEK@ifwtech.demon.co.uk]
	Sent:  Thursday, January 13, 2000 1:27 AM
	To:  amps@contesting.com
	Subject:  Re: [AMPS] Watt meters and PEP


	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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