![background image](http://html2.mh-extra.com/html/icom/ic-f50v/ic-f50v_service-manual_3743880008.webp)
4 - 2
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.
C169
C67
1stIF
C69
R38
C65
R42
L35
C166
C185
C161
C66
C6 1
Q19
C162
R45
C168
C6 2
C165
C167
R46
C188
L33
R43
C70
TA31136FNG
IC1
1 OSCIN
2 OSCOUT
3 M IXOUT
4 VCC
5 IFIN
6 DEC
7 FILOUT
8 FILIN
9
AFOUT
10
QUAD
11
IFOUT
12
R SSI
13
N-DET
14
N-REC
15
GND
16
MIXIN
C68
X1
C71
C163
C63
FI2
I
O
R39
R44
C75
C164
R115
Ref.Freq.
R116
R40
R36
NOIS RSSI
SQLI
SQLO
IF IC
QUADRATURE
DETECTOR
2nd IF
FILTER
TRIPLER
(×3)
NOISE
FILTER
2nd
Mixer
FM
Detector
16
Noise Det.
Noise
AMP
RSSI
11
10
Noise
Filter
2nd IF
AMP
IF IC (TA31136FNG) BLOCK DIAGRAM
9
14
12
2
8
7
3
5
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.
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).
Scrambler/
De-scrambler
TX/RX
HPF
Pre-
emphasis
Limiter Splatter
VR2
Expander
VR4
RXA2
SMF
De-
emphasis
Com-
pressor
VR1
(HPF)
RX
LPF
VR3
(HPF)
7 MOD
18
19
20 SIGNAL
3
TXIN
• BASE BAND IC BLOCK DIAGRAM
23
RXIN
21
SDEC
TXA1
RXA1
BASE BAND IC (IC10)
• 2ND IF AND FM DEMODULATOR CIRCUITS