MM0474
instrument corresponds to the value marked on the panel for the line voltage
available (1/8 amp slo-blow).
c. Introduction.
(1) The Model 432A Power Meter operates with temperature-compensated
thermistor mounts such as the 8478B and 478A Coaxial, and 486A Waveguide
series. The frequency range of the 432A with these mounts in 50 ohm coaxial
systems is 10 mHz to 18 GHz; in waveguide systems it is 2.6 GHz to 40 GHz.
Full-scale power ranges are 10 microwatts to 10 milliwatts (-20 dBm to +10
dBm). Extended measurements may be made to 1 microwatt (-30 dBm). The total
measurement capacity of the instrument is divided into seven ranges, selected
by a front-panel RANGE switch.
(2) This section describes general
operating
procedures
and
error
analysis in microwave power measurement.
d. Controls, Connectors, and Indicators.
(1) The front and rear panel controls, connectors, and indicators are
explained in Figures 18 and 19.
The descriptions are keyed to the
corresponding items which are indicated on each figure.
(2) The COARSE ZERO and FINE ZERO controls zero the meter.
Zero
carryover from the most sensitive range to the six ranges is within 0.5%. When
the RANGE switch is set to COARSE ZERO, the meter indicates thermistor bridge
unbalance, and the front panel COARSE ZERO adjust is for initial bridge
balance. For best results, FINE ZERO the 432A on the particular meter range in
use. For turn on and zeroing procedure refer to Figure 20.
(3) The CALIBRATION FACTOR switch provides discrete amounts of
compensation for measurement uncertainties related to SWR and thermistor mount
efficiency. The Calibration Factor value permits direct meter reading of the
RF Power delivered to an impedance equal to the characteristic impedance (Zo)
of the transmission line between the thermistor mount and the RF source.
Calibration Factor values are marked on the label of each 8478B, 478A or 486A
Thermistor Mount.
(4) The MOUNT RESISTANCE switch on the front panel compensates for three
types of thermistor mounts. Model 486A waveguide mounts can be used by setting
the MOUNT RESISTANCE switch to 100 ohm or 200 ohm, depending on the thermistor
mount used (refer to Table 4). The 200 ohm position is used with Models 478A
and 8478B Thermistor Mounts.
(5) The rear-panel BNC connector labeled RECORDER provides an output
voltage linearly proportional to the meter current; 1 volt into an open circuit
equals full-scale meter deflection.
This voltage is developed across a 1 K
resistor; therefore, when a recorder with a 1 K input impedance is connected to
the RECORDER output, approximately
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