Icom IC-F50V Service Manual page 8

2ND IF AND FM DEMODULATOR CIRCUITS
The 2nd IF circuits consist of 2nd mixer, 2nd IF filter, 2nd
IF amplifier. And it converts the 1st IF signal into the 2nd
IF signal, then filters to remove unwanted signals and
amplifi es. IF IC "TA31136FNG" contains whole of the 2nd IF
circuits and FM demodulator circuit too.
The 1st IF signal is applied to the IF IC, and converted into
the 2nd IF signal, by being mixed with the 2nd LO signal
(from the X2 via the PLL IC (IC4, pins 1, 2) and tripler), at
internal 2nd mixer. The converted 2nd IF signal is filtered by
external 2nd IF filter (ceramic filter), and saturation-amplified
by internal 2nd IF AMP. The amplified 2nd IF signal is
FM-demodulated by the quadrature detector.
The demodulated AF signals "SQLI" are applied to the RX
AF circuits.
• 2ND IF AND FM DEMODULATOR CIRCUITS
C161
TRIPLER
(×3)
RX AF CIRCUITS
The RX AF circuits consist of AF filters, AF amplifier (AF
AMP), AF power amplifier, etc., and amplify, filter the AF
signals FM-demodulated by the FM IF IC.
This transceiver employs the base band IC for audio signal
processing for both transmit and receive. The base band
IC is an audio processor and composed of RF AMPlifier,
compressor, expander, scrambler, etc. in its package.
The demodulated AF signals from the IF IC are applied to
the base band IC (IC10, pin 23). The applied AF signals are
amplified at the amplifier section and level adjusted at the
volume controller section, then suppressed unwanted 3 kHz
and higher audio signals at LPF. The filtered AF signals are
applied (bypassed) the TX/RX HPF, scrambler, de-emphasis
sections in sequence.
• BASE BAND IC BLOCK DIAGRAM
VR1
TXIN 3
(HPF)
TXA1
VR3
RXIN 23
(HPF)
RXA1
SDEC 21
2nd IF
C 166
FILTER
FI2
O I
Q19
C163
C169
Com- Pre-
pressor emphasis
TX/RX
HPF
RX
LPF
Detector
9
QUADRATURE
DETECTOR
R3 9
IF IC
IC1
1
OSCIN MIXIN
2
OSCOUT
3
M IXOUT N-REC
4
C168
VCC N-DET
5
IFIN R SSI
6
DE C I FOUT
7
FILOUT QUAD
8
FILIN AFOUT
TA31136FNG
R4 4
R4 5
NOISE
FILTER
The TX/RX HPF filters out 250 Hz and lower audio signals,
and the de-emphasis circuit obtains –6 dB/oct of audio
characteristics. The expander expands the compressed
audio signals and also noise reduction function is provided.
The AF signals are then level adjusted at the volume
controller section and amplified at the amplifier section, then
output from pin 20 (IC10).
The processed AF signals from the base band IC (IC10) are
applied to the FRONT UNIT via J1 (MAIN) and J401
(FRONT).
The AF signals from the MAIN UNIT "SIGNAL" are passed
through the AF mute SW, LPF and variable register (VR
UNIT) for audio level adjustment, then applied to the AF
power AMP. The amplified AF signals "AFO" are applied to
the internal speaker, or external speaker via the [SP MIC]
jack (MP701; CHASSIS).
Limiter
Scrambler/
De-scrambler
De-
emphasis
4 - 2
IF IC (TA31136FNG) BLOCK DIAGRAM
8
7 5 3
2nd
Noise
Noise
Mixer
Filter
AMP
2nd IF
FM
AMP
Noise Det.
RSSI
12 14
10 11
X1
1stIF
16
15 C6 1
GND
14
13
C6 2
12
11
10
9
R4 3
C188
BASE BAND IC (IC10)
Splatter VR2
Expander
VR4
2
16
7 MOD
SMF
18
19
RXA2
20 SIGNAL