multiplication generally do not multiply the frequency by more than 6. To perform the multiplication of 120, as
shown in figure 106 three stages of multiplication can be used: x6, x4, and x5.
3-8. MIXER
The mixer circuit heterodynes the 60-MHz angle-modulated subcarrier signal from the modulator and the
7,200 MHz injection signal from the multiplier stages to produce a 7,200-MHz modulated carrier to be used as the
up-link frequency.
3-9. TRAVELING-WAVE TUBE
The TWT is a special type of electron tube which provides amplification for wideband signals. The
operation of the TWT depends upon the technique of velocity-modulating the electron beam inside the tube
structure.
3-10.
HIGH-POWER AMPLIFIER
a. Another type of velocity-modulated tube, a klystron, is used to provide the final amplification needed
to raise the modulated signal to the desired power level for transmission. This circuit usually operates with very
high voltages and requires a cooling system to reduce the operating temperature.
b. Several fault detection circuits are used to remove the high voltage or the RF drive from the high-
power amplifier when any defect or malfunction occurs.
Section III. DIRECT-ANGLE-MODULATED TRANSMITTER
3-11.
INTRODUCTION
All angle-modulated transmitters use either direct or indirect methods for producing the angle modulation.
The modulating signal in the direct method has a direct effect on the frequency of the carrier. In the indirect
method, the modulating signal uses the frequency variations caused by phase modulation. In either case, the
output of the transmitter is an angle-modulated wave, and the receiver cannot distinguish between them. A
simplified directly modulated transmitter is shown in figure 107.
3-12.
BASEBAND CIRCUITS
a. The baseband input signal is applied to the voltage-controlled oscillator (VCO). The VCO's output
frequency of 34 MHz is varied in proportion to the baseband input frequency.
b. The amplifier amplifies the modulated subcarrier and applies the signal to the phase detector stage.
3-13.
HARMONIC MIXER
The injection voltage from the multiplier stages is applied to an x4 multiplying circuit within the
harmonic mixer stage. The multiplied output
344 L3
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