On Wed, 24 Jan 2007 07:50:41 -0500, "Jimmie D"
wrote:

After I got my ham ticket I built a little TX with a 6146 and used a light
bulb dummy load. To get an idea of how much power I was putting out I
measure the rsistance of a photo resistor with the tx keyed then applied a
variable ac voltage to the lamp and adjusted it until the resistor measured
the same and calculated power from the voltage and current measurements. I
wonder how accurate this was.

Hi Jimmie,

This was exceptionally accurate. The substitution method here employs
a transfer standard. By bringing the light bulb to the same light
level (the substitution), you have removed any inaccuracy of the
detector, the photo resistor. It has been removed from the sources of
error. Further, you have shifted out of the more difficult domain of
direct RF measurement into 60 HZ where there are a world of tools
(transfer standards) that exhibit very good accuracy.

This is a form of calorimetric measurement, akin to bolometery.

73's
Richard Clark, KB7QHC