3/6/08 888-2463-001 4-15
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
Diamond Series™
The reflected Power sample is also sent to a comparator U44, which has an adjustable
set point. The set point is set for the overload point at R134. When this level is
exceeded, pulse stretcher U21 will send a one second pulse to the CPLD to indicate
VSWR. The main controller will generate an exciter mute. If three strikes occur in a
moving 30 second window the transmitter will turn OFF and operator intervention will
be needed to turn it back ON.
4.6.2.15 Exciter Fold Back references
The Main Controller will control the fold back power of the Exciter at J5-2 and 3. The
signal, EXC_A_FB_REF will give maximum foldback when 5 volts is on the line. Zero
volts will offer no foldback. When the transmitter is in Life Support mode, there will be
no fold back function.
4.6.2.16 Remote Metering
The Forward and Reflected power samples for each PA cabinet are buffered by U36-
U39 before going to the remote metering connection.
4.6.3 Driver
The DD-1 Driver has five major circuit blocks which will be discussed here. These
assemblies are single-rack mounted in a pull out drawer chassis.
4.6.3.1 Driver Preamp
The Preamplifier provides a portion of the overall RF gain of the Driver. A gain control
circuit is also included on the board.
RF enters the Driver Preamp at J1. The input signals are applied to temperature
compensating attenuators R13 and R14 in each of the input paths to provide the overall
gain of this path and compensating for gain variations with temperature. The output of
the attenuators is summed by a phase combiner T5 and applied to the quadrature hybrid
T2. The Hybrid T2 and associated components act as an attenuator in this path.
With no current in PIN diodes CR1 and CR2, R1 and R2 provide a nominal impedance
termination for T2 ports 1 and 4 and therefore a minimum of signal transmission from
the input (6) to the isolated (3) port.
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