Re: [Amps] Measuring RF Power

[David Kirkby <david.kirkby@onetel.net>]

Bill Fuqua wrote:

>I think if we just package all the emails about this subject and keep the 
>"package" attachment  handy for the next time this  comes up just send it 
>to the person with the question instead of going thru this again and again 
>over the years. I know we have gone thru this exercise twice maybe three 
>times already.
>
>73
>Bill wa4lav
>  
>

Looking back over the archives I see it has come up before as you say, 
although not very often. The ratio of discussions on parasitic 
oscillations must outnumber it 1000:1, with very much the same arguments 
being slung around about parasitic oscillations each time.

In one post on RMS power

http://lists.contesting.com/archives//html/Amps/2001-06/msg00315.html

you personally gave an example of some numerical data where you computed 
RMS and mean powers and then went on to say

"OK above is your RMS power for what ever good it is.... But does give 
you 22.5% bigger  number in this example."

Some knowledge has been added, as the ratio P_rms/P_mean has been shown 
to be sqrt(3/2)=1.22474  if the load is resistive - not just in the 
example you gave.

Just in summary for *resistive* loads

P_mean=V_max^2 / 2R
P_rms = sqrt(3/2) V_max^2 / 2R
P_rms/P_mean=sqrt(3/2).

For reactive loads ??? That could be interesting.

-- 
Dr. David Kirkby, 
G8WRB

Please check out http://www.g8wrb.org/ 
of if you live in Essex http://www.southminster-branch-line.org.uk/



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