MM0474
Figure 12.
Feedback Differential Amplifier.
and the RANGE switch to change metering loop gain so that the meter will read
full scale for each power range.
Potentiometer adjustments are provided to
accurately set the calibration on each range. Diode A1CR6 provides temperature
compensation for A1Q10.
n. Meter Circuit.
A simplified schematic diagram of the meter circuit is shown in Figure
14.
The meter circuit includes feedback current-squared generator A1Q11, a
squaring circuit, the meter, RECORDER/LEVELER and DVM jacks, J2 and J4.
The
purpose of the meter circuit is to convert a linear voltage function,
proportional to the square root of applied power, to a square function so that
power may be indicated on a linear meter scale. The linear voltage function is
applied to the base of A1Q11 and is converted to a square law function by the
squaring circuit in series with A1Q11 emitter.
o. Metering Circuit Differential Amplifier.
(1) The metering circuit RECORDER/LEVELER output is a voltage of low
source impedance necessary for isolation between a recorder or leveler
amplifier and the metering circuit of the power meter. The isolation circuit
comprises the differential amplifier A2Q6-A2Q7 and output transistor A2Q8. The
voltage developed across A2R38 for the DVM output is referenced at the base of
A2Q6 for comparison to the voltage at the RECORDER/LEVELER jack placed on the
base of A2Q7. Any difference voltage creates an error voltage that changes the
base-emitter bias on
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