Measuring a power through a voltage (or current) is an indirect way to
estimate something we're not really measuring.
A conventional power meter is not measuring a power but the voltage (or
current) of a complex signal. In a complex AC it's correct to talk about RMS
as the closest equivalent.
Evaluating RMS as .707 of the peak would be true with pure carrier sine
waves but its very confortable to utilize the diodes and a suitable RC time
constant to rectify peak voltage as a DC level.
Obviously, in a DC voltage the RMS and the AVG are coincident but this DC is
not existing beeing only created in the Wattmeter itself.
All considered, a complex envelope like a modulated signal creates a big
deal when approximations are not accepted.
73,
Mauri I4JMY
----- Original Message -----
From: Dave D'Epagnier <DAVED@ctilidar.com>
To: Dave D'Epagnier <DAVED@ctilidar.com>; AMPS <amps@contesting.com>; 'Ian
White, G3SEK' <G3SEK@ifwtech.demon.co.uk>; 'measures' <measures@vcnet.com>
Sent: Thursday, January 13, 2000 7:57 PM
Subject: RE: [AMPS] Watt meters and PEP
>
>
> A 200w peak signal into a 1 ohm load would have a voltage amplitude of
> 14.14volts. The average power would be Vrms squared / R or 100v/1ohm =
> 100Watts. This is average power, which is the dc equivalent heating
ability.
> Power (unlike voltage or current) is always positive. There is no reason
or
> need to evaluate it's rms level.
> ----------
> From: measures [SMTP:measures@vcnet.com]
> Sent: Thursday, January 13, 2000 10:18 AM
> To: Dave D'Epagnier; AMPS; 'Ian White, G3SEK'
> Subject: RE: [AMPS] Watt meters and PEP
>
>
> ? RMS is equivalent DC heating ability. For example, with a
> sine-wave,
> 200w-pk would have the heating ability of 100DC watts. .
>
> cheers, Dave
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
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