Antonio Vernucci wrote:
My question concerns the well known Struthers RF Wattmeter
TS-1285/URM-120 which has three big plug-ins (2-30 MHz 1000 Watts,
25-250 MHz 500 Watts, 200-1000 MHz 500 Watts).

Differently from all common wattmeters, the Struthers meter has a
perfectly linear scale. How could they achieve that?

On QST magazine (May 1996, pag. 77) K3BRS states that replacing the
diode with a different type would cause the initial part of the scale to
become very inaccurate.

Does anyone know of special diodes resulting in a linear wattmeter scale?

73

Tony I0JX

If you operate a diode detector in the "square law" region, the voltage
output is proportional to the incident power. You don't get a huge
dynamic range where this is true (10-20 dB, perhaps?), but on the other
hand, people have been building diode detector based power meters for
decades. Different diodes have different curves, so changing diode type
would affect the calibration.