Section F
RF Multimeter (A23)
F.1
Introduction
This section describes the RF Multimeter board.
The RF Multimeter provides metering of the Predriver and
Driver sections of the transmitter. A probe, with four meter
positions, is also provided for AC and DC voltage measurements
on printed circuit boards in the transmitter’s non-interlocked
compartment. The RF Multimeter is located on the back of the
Driver Compartment door. The probe is located in the Center
Control Compartment.
Refer to SECTION V, Maintenance, for pc board maintenance
procedures. There are no adjustments on this board.
F.2
Circuit Description
Refer to the RF Multimeter Schematic, 839-6208-230, in the
Drawing Package.
The meter has a 100 microampere movement, and two scales,
0-3 and 0-10. The meter switch positions are labeled with the
name of the metered function and the scale used. For some
positions, a X10 or X100 multiplier is applied to the meter scale
reading.
Meter M1 is protected against excessive voltages and currents by
1-Amp rectifier diodes CR4 and CR5. Capacitor C3 provides RF
bypassing around the meter movement.
F.2.1
M e t e r i n g D r i v e r S e c t i o n Pa rameters
For 0-3 Volt, 0-30 Volt, and 0-300 Volt DC ranges, the multimeter
is a 10,000 Ohm per Volt meter. For current ranges, the meter acts
as a voltmeter, measuring the voltage drop across a resistor in the
DC current path. One side of the meter is grounded through a
section of switch S1 for Driver stage voltage measurements. The
meter is isolated from ground for current measurements.
The RF Multimeter positions are defined and detailed in the
Sections where the meter resistors are located. These positions
are as follows:
PREDRIVER
PREDRIVER
CONTROL
DRIVER
DRIVER
DRIVER 8A
DRIVER 8B
F.2.2
Multimeter Probe
The multimeter uses a flexible coiled patch cord with a clip-on
probe for convenient measurement of voltages in the non-inter-
locked compartment. Measurement ranges available are 0 to 30
Peak AC Volts, 0 to +3 VDC, 0 to +30 VDC, and 0 to -30 VDC.
Resistor R5, 29.4K 1%, is the multiplier resistor for the 0-3 Volt
range. The total 30K resistance required for this range includes
the meter resistance.
Resistor R3, a 301K 1% resistor, is the multiplier resistor for the
0-30 Volt range. Positive and negative voltage ranges are ob-
tained by grounding either the negative or positive meter terminal
through S1.
For AC Voltage measurements, CR1, R4, C1 and R1 make up a
peak detector. Resistor R2 is the multiplier resistor for the AC
voltage range.
888-2297-002
F-1
WARNING: Disconnect primary power prior to servicing.
