EFJohnson 764X User Manual
Page 54
UHF (7640) CIRCUIT DESCRIPTION
5B-11
November 1998
Part No. 001-7600-001
The phase detector determines the phase differ-
ence between these signals and then produces output
pulses on pin 8 which are filtered by the loop filter.
This filter consists of Q34, R180, R181, and C202-
C204. The output of this filter is the DC control volt-
age applied to the VCO. The phase detector increases
or decreases this control voltage to change the VCO
frequency.
5.7.2 VCO CIRCUIT
Separate receive and transmit VCOs are used.
The receive VCO consists of Q23/D20/D34 and the
transmit VCO consists of Q25/D22/D33. The signal
from these VCOs is amplified by buffer amplifiers
Q28 and Q29 and is then applied to T/R switch D18
and D19. The VCO receive injection signal is applied
to first mixer Q3, and the VCO transmit signal is
applied to driver Q21. Part of the Q28 output signal is
amplified by Q29 and fed back to PLL IC10, pin 2 as
described in the preceding section.
5.7.3 UHF POWER SUPPLY
5.7.4 UHF CPU IC1 PORT ALLOCATION
Line Description
VCC
Unswitched input voltage to the transceiver.
HV
VCC supply voltage switched by Q14 and Q15.
When the [POWER] switch is pressed, the CPU
outputs the “PWON” control signal to this circuit
to turn the HV supply on.
CPU5V Common 5V supply for the CPU produced from
the VCC supply by CPU5V regulator IC3. The
circuit outputs this voltage regardless of the
transceiver on-off condition.
8V
Common 8V supply produced from the HV
supply by 8V regulator IC2.
5V
Common 5V supply produced from the HV
supply by 5V regulator Q12/Q13.
R8
Receive 8V supply produced by R8 regulator
Q10/Q11 using the “TXC” signal from I/O
expander IC13.
T8
Transmit 8V supply controlled by T8 regulator
Q8/Q9 using the “TMUT” signal from I/O
expander IC13.
Pin
No.
Port
Name
Description
1
VIN
Input port for overvoltage detection from
the vehicle power source.
12
SCK
Outputs clock signal to EEPROM IC3,
PLL IC10 (main unit) and expanders
IC12, IC13 (main unit), etc.
13
SI
Input port for the data signal from
EEPROM IC3, etc.
14
SO
Outputs data signal to EEPROM IC3, PLL
IC10 (main unit) and expanders IC12,
IC13 (main unit).
16
CLIN
Input port for cloning signal.
17
CLOUT Output port for cloning signal.
18
POSW
Input for the POWER switch. Low =
POWER switch pushed.
19
NOIS
NOIS signal input port from the FM IF
IC1 (main unit) for noise squelch
operation.
26
PTT
Input port for the PTT switch. Low = PTT
switch pushed.
32
RFATT
Outputs RF attenuator control signal to the
attenuator switch (Q1 on main unit).
Low = Attenuator function on.
36
UNLK
Input port for PLL unlock signal from the
PLL IC10 (main unit). High = unlock.
37
PWON
Outputs control signal for the power
switching circuit (Q14/Q15 on main unit).
38
DIM
Outputs control signal for LCD backlight.
Low = LCD backlight on.
39
EXTPTT Input port for the PTT switch from exter-
nal connector J5 (main unit). Low =
External PTT switch on.
40
DIM
Input port for the LCD backlight control
signal from external connector J5 (main
unit). Low = External dimmer switch on.
41
PLST
Outputs strobe signals for PLL IC10 (main
unit).
42
DAST
Outputs strobe signals for level controller
IC12 (main unit).
43
EXST
Outputs strobe signals for the I/O
expander IC13 (main unit).
45,
46
KS1,
KS2
Output ports for the key matrix.
47-
50
KR3-
KR10
Input ports for the key matrix