3. The transmitter injection unit contains circuits which prepare the input signals for application to the
a. Tracking filters are used in some injection units to filter the synthesizer's input signal frequency
spectrum to improve the S/N. The tracking filter is basically a VCO that has a phase-lock-loop circuit. The
output of the VCO is locked to the input frequency through the action of the phase-lock-loop circuit.
b. Basically, the oscillator-synchronizer functions in the same manner as the tracking filter. The main
difference is that the input signal is compared with a reference signal, but there is no oscillator output signal.
Instead of the conventional oscillator output, there is an output error signal which is used to control another
c. Multipliers are used in some injection units to raise the frequencies to the values required for efficient
operation in the translator unit.