Figure 106. Indirect-angle-modulated transmitter.
c. The baseband amplifier increases the power level of the baseband signal and isolates the shaping
circuits from the modulation amplifier.
3-5. MODULATOR
The prepared baseband signal and the unmodulated 60-MHz subcarrier signal are combined in the
modulation amplifier to form the modulated-subcarrier signal. The indirect-modulation process in this amplifier
involves amplitude-, phase-, and frequency-modulation techniques.
3-6. TRANSMITTER INJECTION STAGES
a. The transmitter injection voltages are usually generated by a separate frequency-generating
subsystem. This subsystem usually contains a highly stable frequency standard, amplifiers, and frequency
synthesizers. In addition to the injection output used in the transmitter, the subsystem also provides
synchronizing voltages for other subsystems within the communication system.
b. The transmitter injection voltage can also be developed by a single highly stable oscillator. For
example, the stage illustrated in figure 106 could be a single crystal oscillator stage operating at a frequency of 60
MHz.
3-7. FREQUENCY MULTIPLIERS
The frequency of the transmitter injection voltage is multiplied by a series of multiplying stages to a value of
approximately 7,200 MHz, the frequency required for transmission. The individual circuits used to perform this
344 L3
108
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