[Elecraft] Power Measurement - Where am I wrong?

[Ron D'Eau Claire]

Yes, you have the right formula, Fran. 

Power = (Vpk-pk)^2/8R 
Where R is the load resistance. 

It is *not* frequency sensitive, but hardware often is. 

Either your scope probe is not properly frequency-compensated or your load
is not a good, solid 50 ohm non-reactive dummy load. Note that it's very
hard to try to make these measurements into a real antenna, even if the SWR
indicator says 1:1. That's because most SWR meters are no where near
accurate enough.

First step, I'd bypass the KAT2 in case it's inserting reactance, trying to
"adjust" the tuning into a 50 ohm dummy load. 

Ron AC7AC

-----Original Message-----
I do not have a power meter so I figured that I could compute power from a
peak to peak measurement using my scope.  This should be accurate enough for
ballpark knowledge. However, the measured voltage increases as frequency
increases with the 10 meter voltage being nearly double the 80 meter
voltage.  This would mean power increases with frequency unless the formula
I was going to use is missing a frequency dependent component.

I have a KAT2 installed and I used a good 50 ohm resistive load.

My math follows:

Vrms = Vp-p/(2*sqrt(2))
Vrms = Irms*R assuming purely resistive load
or Irms = Vrms / R

if Prms = Irms*Vrms
substituting yields
Prms = (Vp-p * Vp-p) / (8 * R)

I know that Pave = Prms / 2
but that does not help much because I would still get more than 10 Watts out
on 10 meters when set for 5 watts out.

Where did I go wrong?

Fran