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Page: 21 Of 57
Model No: 3420
Drawing No:
Customer :
Model No:
H 520 PLUS
Rev. Date:
3. DESCRIPTIONS OF EACH BLOCK
A. Introduction
The synthesizer is implemented with the following
Components:
- PLL IC (IC302)
-
X-TAL
(X302)
-
VCO,
VARICAP
DOIDE
(D301)
IC302 is a cmos LSI that includes most of PLL block and driver, the Q301, C305, C306, C304, C301 and T302,
Varicap diode D301 are clapp oscillator circuit to operate as a VCO of the IC302. Q301 is a switching transistor to
connect or disconnect the tuning capacitor in the VCO oscillator tank circuit for transmitter or receiver. Q304
works as a buffer AMP for RX local frequencies (16 MHz) and TX generating frequencies (13 MHz).
B. Reference frequency
The crystal, X302 (4.50 MHz) and other components of IC302 can make a reference frequency oscillator with
internal amplifier.
C. VCO
Q301 and surrounding parts are consisting a clapp oscillator works as a VCO of IC302. the VCO can be oscillate
over the required of 13.4825 MHz to 17.29625 MHz
D. Phase detector and VCO control
The detector is a digital phase comparator which compares the phase of the reference signal with programmable
divider output square waves and develops a series of pulses whose DC level depends on the phase error of each
signal.
E. Transmitter/Receiver buffer AMP
Output signal of Q301 is fed into buffer AMP Q302,
F. Transmitter doubler
The output signals of Q302 goes to an amplifier with tuning circuit Q201, T203, T204 which doubles incoming 13
MHz signals.
G. Switching of tuning capacitor in VCO
The VCO circuit must tune with a wide rang of frequencies 13.4825 ~ 13.7025 MHz (EU), 13.800625 ~
13.995625 MHz (UK) for transmitter and 16.270~16.710 MHz (EU), 16.90625 ~ 17.29625 MHz (UK) for receiver.
To comply above range of VCO, the tuning capacitance should switched for transmission or reception.