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2-32
Theory of Operation
: Voltage Control Oscillators (VCO)
Both the normal and adapt charge pumps get their supply from the capacitive voltage multiplier
made up of C247, C283, C284, C285, C286, and triple diodes D210 and D211. This circuit provides
13.3V at U205, pin 47.
Figure 2-21. Low Band Synthesizer Block Diagram
2.19 Voltage Control Oscillators (VCO)
2.19.1 Receive VCO
The receive VCO is a Colpitts type design and using two active devices in parallel, Q202 and Q204.
The oscillator is powered off of the 4.3 volt super filter supply when the AUX3 line goes low. The
oscillator operates from 139 to 152 MHz for range 1 and 145 to 160 MHz for range 2. The frequency
is tuned by varactor diodes CR201 and CR202.
2.19.2 Transmit VCO
The transmit VCO is a Hartley-type design with active devices Q203. The oscillator is powered off of
the 4.3 volt super filter supply when the AUX2 line goes low. The oscillator operates from 29.7 to
42 MHz for Range 1 and 35 to 50 MHz for Range 2. The frequency is tuned by varactor diodes in
U203. Note that the values of the inductive tap, L208 and L209, and the capacitor C215 which
couples the varactor to the oscillator tank vary between the ranges.
2.19.3 Buffer
Both the receive and transmit VCO are fed to a buffer amplifier Q201. This is a BJT amplifier that
boosts the signal levels to +4 dBm and provides reverse isolation to the oscillators. The amplifier is
powered off the 4.3 volt super filter supply and the feed network is combined with the transmit filter.
DATA
CLK
CEX
MODIN
V
CC
, DC5V
XTAL1
XTAL2
WARP
PREIN
VCP
Reference
Oscillator
Voltage
Multiplier
Voltage
Controlled
Oscillators
Switching
Network
2-Pole
Loop Filter
DATA (U409 Pin 100)
CLOCK (U409 Pin 1)
CSX (U409 Pin 2)
MOD IN (U404 Pin 40)
+5V (U204 Pin 4)
7
8
9
10
13,30
23
24
25
32
47
VMULT2
VMULT1
BIAS1
SFOUT
AUX3
AUX2
IADAPT
IOUT
GND
FREFOUT
LOCK
4
19
6,17,22,29,31,33,44
43
45
1
2
28
14
15
40
Filtered 4.3V
Steering
Line
LOCK (U409 Pin 56)
Prescaler In
LO RF
Injection
TX RF
Injection
(First Stage of PA)
FREF (U303 Pin 21 & U404 Pin 34)
39
BIAS2
41
(U400 Pin 1)
V
DD
, 3.3V
MODOUT
U205
Low Voltage
Fractional-N
Synthesizer
5,20,34,36
Summary of Contents for PR860
Page 1: ...PR860 Two Way Portable Radio Detailed Service Manual ...
Page 2: ......
Page 5: ...iv Notes ...
Page 9: ...viii Table of Contents Notes ...
Page 13: ...Notes xii List of Figures ...
Page 17: ...1 4 Introduction Radio Model Information Notes ...
Page 51: ...2 34 Theory of Operation Voltage Control Oscillators VCO Notes ...
Page 81: ...4 4 Schematic Diagrams Overlays and Parts Lists Flex Layout Notes ...
Page 193: ...4 116 Schematic Diagrams Overlays and Parts Lists Low Band Section Notes ...
Page 196: ......