a. If a direct-angle modulation technique is used, the baseband signals (after preparation) are applied
directly to the subcarrier oscillator circuit to produce the desired type of angle modulation. If low values of
oscillator frequency and frequency deviation exist, it may be necessary to include a number of multiplier stages
to raise them to the desired values.
b. If indirect-angle modulation techniques are used, the baseband signals and the output of the subcarrier
oscillator are applied to a modulation-amplifier circuit to produce the desired type of angle modulation.
4. After modulation, the signal generally undergoes additional amplification in an RF amplifier stage. The
signal is then coupled to the exciter-translator unit in the transmitter.
SECTION IV. INDIRECT-ANGLE-MODULATED TRANSMITTER
LEARNING EVENT 16: INDIRECT-ANGLE MODULATION
Most transmitters amplify and multiply an angle-modulated signal up to the desired frequency and power level.
The block diagram of a simple indirect-angle-modulated transmitter is shown in Figure 2-14.
Figure 2-14. Indirect-angle-modulated transmitter.
SS0031
2-14
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