On Tue, 23 May 2006 12:16:27 +0100, "Reg Edwards"
wrote:

Replace the meter scale with a white card and calibrate it yourself
with pen and ink. You will also need a signal generator and an
attenuator.

If you derive the S-meter reading from the a.g.c. control voltage, be
prepared to perform the calibration at various temperatures, since the
gain of simple IF-strips vary with temperature (and thus need a
different amount of a.g.c.), unless the gain is controlled by passive
components only.

With various front end filter for various frequency bands and
attenuation depending of the frequency, you would have to perform the
calibration on several frequencies.

Instead of a pen and ink, it would be more practical to use a micro
controller with sufficient non-volatile storage for the conversion
tables and use analog inputs for a.g.c. voltage and temperature and
some kind of input for the frequency being received. With these inputs
and the conversion table, a voltage proportional of the log of the
antenna terminal power could be generated.

Paul OH3LWR