5 - 1
1ST IF CIRCUITS
The RX signals from the BPF are mixed with the 1st LO
signals to be converted into the 46.35 MHz 1st IF signal.
The 1st LO signals are generated by the RX VCO (Q14,
D33, 62, 63), and passed through the LO SW (D15) and
attenuator, then applied to the 1st mixer (Q3)
The converted 1st IF signal is filtered by the crystal filter (FI1)
and amplified by the 1st IF AMP (Q4), then applied to the IF
IC (IC1).
5-1 RECEIVER CIRCUITS
RF CIRCUITS
RF signals from the antenna are passed through the LPF (as
the harmonic filter for transmitting) and antenna SW, then
applied to the RX BPF circuit.
The applied RX signals are passed through the 2-staged
tuned BPF (D8, 20 and D4, 21) to remove unwanted out-of-
band signals, and amplified by the low-noise RF AMP (Q2),
then applied to the 1st mixer (Q3) via three BPFs (D9, 10
and D19).
Each BPF is tuned to the RX frequency by the tuning
voltage “T1” and “T2” from the D/A converter (IC20), to
obtain required IMD characteristic.
2ND IF AND DEMODULATOR CIRCUITS
The amplified 1st IF signal is mixed with the 2nd LO signal
at the internal 2nd IF mixer of the IF IC (IC1), to obtain the
450 kHz 2nd IF signal.
The 15.3 MHz signal generated by the reference oscillator
(X2) is passed through the filter AMP (Q34) to extract the
45.9 MHz 3rd harmonic component. The 45.9 MHz signal is
then applied to pin 2 of IF IC (IC1) as the 2nd LO signal.
The converted 2nd IF signal is output from pin 3 of IF IC
(IC1), and filtered by the ceramic filters (FI2 and FI6 for
Narrow mode; FI2 only for Wide mode) to remove unwanted
out-of-band signals, then applied to the internal frequency-
demodulator of IF IC (IC1) from pin 5.
The demodulator is a quadrature type which uses X1 as the
phase shifter.
The frequency-demodulated AF signals are output from pin 9
to AF circuits.
• RF CIRCUITS
• 2ND IF AND DEMODULATORCIRCUITS
• 1ST IF CIRCUITS
SECTION 5. CIRCUIT
DESCRIPTION
LPF
LP F
PWR
DET
D1,11,12
ANT
SW
D3,5,6
BPF
D10
BPF
D9
BPF
D4,21
BPF
D8,20
RF
AMP
Q2
AGC
Q1
Tuning voltage “T2”
To 1st IF circuits
BPF
D19
Tuning voltage “T1”
RSSI
From the TX AMP
TX/RX
SW
D14,15
Q3
1st mixer
BPF
XTAL
FI1
IF
AMP
Q4
LPF
From RF circuit
To IF IC
To 1st IF circuits
46.35 MHz
1st LO signals
(182.35 MHz-220.35 MHz)
REF
X2
X3
Q34
X1
BPF
BPF
CERAMIC
FI6
W/N
SW
Q5
BPF
CERAMIC
FI2
W/N
SW
D56
W/N
SW
D57
D/A
IF IC
From 1st IF circuits
IC1:TA31136FN
IC18
AK2330
NWC
15.3MHz
45.9MHz
DISC
SQIN
450kHz
To the AF circuits
NWC