Analog Circuits Cookbook

Measurements (rf) 137

temperature by the surrounding metal work. A differential amplifier com-

pares the outputs of the two diodes and controls an attenuator situated

between an oscillator and a level indicator. The former works at a conve-

nient comparatively low frequency and high level, so that high linearity is

easily achieved in the latter. Further attenuation can be introduced in

steps,

to allow for ranges down to the tangential sensitivity, either manual-

ly by the operator (in which

n

n n

n

MAIN UNIT

Measuring head (with matched diodes)

Figure

5.3 Accurate rf level measurement requires linearisation of the diode

response. This can be done ...