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(6) Electric Field Detect in Circuit
The electric field detection circuit comprises a noise amplifier and a noise detection circuit. If the output from
the circuit is high level, the information "no signal detected" is sent to MPU IC501. If the output is low level,
the information "signal detected" is sent to MPU IC501.
The AF output from the RF unit is amplified by Q503 and, at pins 55 and 54 of IC502, noise signal only are
extracted by an approximately 10KHz band-pass Filter. Wave detection is performed by the noise detection circuit
built into IC502, and the result is output as logical output to pin 48 of IC502.
IC502
R511
(1pin)
AF
C503
13-5. CIRCUIT OPERATION OF RF UNIT
(1) PLL Circuit
IC201 includes two PLL circuits for transmission frequency and reception local frequency.
The frequency in the band of 900 MHz supplied from TX VCO and RX VCO, and Ref. OSC frequency (12.8
MHz) are divided into 12.5 kHz frequency controlled by the CPU. The phases of the frequency from TX and RX
and the reference frequency are compared each other, the control voltage is supplied to the VCO circuit from
pins 7 and 18 so that the desired TX and RX frequencies are provided. The VCO control signal (TX, RX fre-
quency setting) of the PLL circuit is supplied to CPS pin 15, SI pin 16 and RST pin 17 from the CPU circuit.
Also, the locked oscillation frequency of the VCO circuit is supplied to the CPU from pin 14 at "L".
TX VCO
C208
from VCO201
Control
voltage
R202 R203
C204
R204
to TX VCO
C216
10
LPF (TX)
C215
11
12
C214
Ref. OSC. 12.8MHz
R514
C504
C505
R513
C502
R512
Q503
C501
R515
1
NC
2
TXO
3
Vcc
Frequency TX
4
TXB
Demultiplication
5
TXE
6
GND
Phase Comparator
7
PD1
8
Vcc
OSC+1/2
Frequency Ref
9
XIN
Divider
Demultiplication
XOUT
XB
GND
IC201
Circuit Diagram
R517
R516
R518
VR
C507
501
C508
55
54
52
NOISE
AMP
IC502
Circuit Diagram
MIXR 24
MIXIN 23
Vcc 22
Frequency RX
RXB 21
Demultiplication
RXE 20
GND 19
Phase Comparator
PD2 18
RST 17
SI 16
CPS 15
LD 14
MIXO 13
| 175 |
C509
R520
R519
49
48
SQ 2
DET 2
C240
C241
C242
RX VCO
from VCO202
R231
R225
R222
LPF (RX)
CPU circuit
KX-F910BX
IC501
(68pin)
Control voltage
to RX VCO
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