User Manual

Technical Description
Version 4 4-6 04/02/04
Loop Filter
The loop filter is a low-pass filter, which is designed to give the
phase-locked loop the desired characteristics in response to
transient change in the output voltage from the frequency
synthesizer. The low-pass filter is realized as a passive filter. The
filtered output signal controls that output frequency of the VCO.
Voltage-Controlled Oscillator (VCO)
The VCO generates an output frequency of 139.3 to 163.3 MHz.
After phased-locking and amplification, the output frequency of the
VCO is the carrier frequency (139.3 to 163.3 MHz).
Amplifier
The amplifier outside the loop is used to amplify the carrier signal
from the channel PLL. The amplified carrier is fed to the mixer,
where it is mixed with the modulated signal from the modulator.
4.3.2.2 Upconverter
The upconverter is designed for broadband operation. It transforms the
modulated signal of 10.7 MHz ± deviation to a frequency in the range of
150 to 174 MHz.
Phase Detector
The phase detector is used to control the output frequency from the
VCO and will stabilize the frequency of the VCO when the channel
is maintained.
An output voltage from the phase detector controls the output
frequency from the VCO. This output voltage is not sufficient to
carry out a channel shift. The frequency synthesizer is used to
achieve channel shifts. Inputs to the phase detector are the
modulation signal of 10.7 MHz from the modulator, via an amplifier,
and the intermediate frequency of 10.7 MHz from the mixer, via an
amplifier.
The phase detector will detect a difference in phase between the
two input signals, and the output voltage of the phase detector will
depend on the size of the phase difference. The output voltage
from the phase detector is DC-offset and then applied to a varactor