Re: Re: power measurement

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From: janderson@polycom.com
Date: Wed Jun 08 1994 - 17:51:36 EDT


                           
                           _
For a sine wave, Vrms is \/2 Vpk ("peak voltage"), and Vpk is 1/2 Vpk-pk
("peak to peak" voltage). Which is what you figured....

_______________________________________________________________________

John:

        Careful! - I made the same mistake yesterday on this list...

           Vrms = ((2**(1/2)) / 2) * Vpk, rather than (2**(1/2))*Vpk.
                              ^^^
                      (note the divide by 2)

        Stated another way, Vrms = 0.707 * Vpk, rather than 1.414 * Vpk
(otherwise you'd have Vrms > Vpk !!).

        And from this, Power = (Vp-p **2) / (8 * Rload), which is a useful
calculation if taking measurements with a scope. (Someone else out there might
want to check this to see if I've made a mistake).

Cheers from the bonehead,
 
- Jeff, WA6AHL


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