2. The photocell will sense an arc in the output waveguide and will apply the signal to the arc detector. The
output of the arc detector will cause the diode switch to remove the RF drive from the klystron power amplifier.
3. The reverse directional coupler samples the reflected energy to the waveguide. When the voltage standing
wave ratio exceeds a predetermined value, the reflected power switch and the arc detector will cause the RF
drive to be removed from the klystron power amplifier.
SECTION VI. TRANSMITTER ANALYSIS
LEARNING EVENT 30: TRANSMITTER INJECTION
Voltages used for transmitter injection can be considered as an additional subcarrier's output. The frequencies
will be mixed with the modulator's output in the translator portion of the transmitter to form the final angle-
modulated output signal.
LEARNING EVENT 31: FREQUENCY GENERATOR SUBSYSTEM
The frequency generator subsystem provides signals that are used throughout a microwave communications
station. All of the frequency outputs of this system are derived from a frequency standard. The frequency
standard produces an extremely accurate output signal which is continually monitored and compared with
appropriate frequency references. An error in the frequency standard's output can be corrected through
adjustments. The output of the frequency standard is coupled to the injection units through a synthesizer driver,
frequency synthesizers, and an injection patch panel. (See Figure 2-16, page 2-20.) These simplified block
diagrams represent the techniques used in one particular station, but similar techniques will be used in other
types of stations to develop the required injection voltages.
1. The synthesizer driver, using the frequency standard's output signals, develops the fixed frequencies needed
to drive the frequency synthesizers. In this particular example, the synthesizer driver receives an input of 5
MHz from the frequency standard, divides it to 1 MHz and develops 22 different output frequencies which are
used as the inputs to the frequency synthesizers.
2. The frequency synthesizers contain circuits which are capable of converting the relatively few (22) fixed
input frequencies into outputs that can be varied from 0.01 Hz to 50 MHz in selectable steps as low as 0.01 Hz.
Frequency selections are made by the push buttons on the front panels of the frequency synthesizer unit.
2-19
SS0031
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