[Amps] Power meter calibration

[Steve Thompson]

On Monday 06 October 2003 10:40, Martin Sole wrote:
> Apologies if this is not really amps but lots of wise old owls on here
> methinks.
>
> I have built a power meter, to measure the power out of my amplifier,
> hopefully that keeps this on track. I have a question concerning
> calibration. Ignoring diode non-linearity's and other spurious
> imperfections, what sort of law should the meter scale be calibrated
> according to. I have the WB6BLD meter scale drawing program for which
> the included 200 watt scale uses a linear exponent of 0.55. Having tried
> this it just doesn't seem right. What's the formula?

There isn't a simple single formula, it depends on the characteristics of the 
diode, and the rf voltage and dc current. In some designs, the diodes are 
used with rf voltages where the diode drop is significant. Also, at very low 
currents, diodes can have different characteristics. If the rf voltage is a 
lot higher than the diode threshold, then a simple square law should suffice.

Is absolute accuracy all that important? If you want to check that your 
station is working ok, then repeatability is what you need.

Steve