Transmitter Circuits - Icom IC-F5220D Service Manual

RX AF CIRCUITS
The detected audio signals adjusted by the linear codec's
electoronic volume (inside the AF CUSTOM IC (IC1010)).
The level-adjusted AF signal is then amplified by the pre-
AMP (IC1004) and AF power AMP (IC1009).
The power amplifi ed AF signal is passed through the exter-
nal speaker jack (J1002), and then applied to the internal
speaker.
• RX AF CIRCUITS
IC1010
From the IF IC
IC1004
AFVO
AF AFO
AMP
Electronic
volume
SQUELCH CIRCUITS (Analog mode only)
The squelch circuit cuts off the AF output signals when no
RF signals are received. Detecting noise components in the
demodulated AF signals, the squelch circuit stops audio sig-
nals being heard.
A portion of the demodulated AF signal from the IF IC (IC4)
is passed through the AF CUSTOM IC (IC1010) for level
(=threshold) adjustment. The level-adjusted AF signals are
passed through the noise fi lter (IC4, pins 7, 8 and Q9, R42,
R44–R45, C68–C70) to fi lter only the noise components (ap-
proximately 30 kHz signals). The noise components are rec-
tified, resulting in a DC voltage corresponding to the noise
level.
If the noise level is higher than the preset one, the internal
comparator set the "NOISE" signal to the CPU to "High," then
the CPU turns the "AFON" signal, which controlls the AF
mute SW, (Q1008, Q1012, D1007) to "Low," to stop the AF
output.
• SQUELCH CIRCUITS
NOISE SQUELCH DIAGRAM
To RX AF circuits
7
14 15
Noise
DAC
8
AMP
IC1006
From IF IC
Noise filter
(IC4, Pin16)
J1002
IC1009
Ext.speaker
AF
AMP
FRONT UNIT
SP1
Int.speaker
"NOIS"
13
Com-
Noise
parator
detector
IC4

5-2 TRANSMITTER CIRCUITS

TX AF CIRCUITS
The audio signal from the microphone (MIC signal) is passed
through the MIC gain SW (IC53), and then applied to the AF
CUSTOM IC (IC1010).
• WHILE OPERATING IN THE ANALOG MODE
The amplifi ed MIC signal is passed through the HPF (inside
the AF CUSTOM IC (IC1010, pin 3)), which attenuates fre-
quencies 300 Hz and below, and then applied to the limiter
AMP (inside the AF CUSTOM IC (IC1010, pin 4)). The am-
plitude-limited MIC signal is applied to the AF CUSTOM IC
(inside the IC1010).
The MIC signal is converted into a digital audio signal by
the linear codec (inside the AF CUSTOM IC (IC1010)), pro-
cessed by the DSP (IC2007), and then converted into an
analog baseband signal (modulation signal).
• WHILE OPERATING IN THE DIGITAL MODE
The amplifi ed MIC signal is applied to the ALC (inside the AF
CUSTOM IC (IC1010, pin10)) which keeps the signal level
fi xed.
The level-adjusted MIC signal is applied to the linear codec
(inside the AF CUSTOM IC (IC1010)) through the MIC line
SW (inside the AF CUSTOM IC (IC1010)).
The MIC signal is converted into a digital audio signal by
the linear codec (inside the AF CUSTOM IC (IC1010)), pro-
cessed by the DSP (IC2007), and then converted into the
digital baseband signal (modulation signal).
The signal from the linear codec (inside the AF CUSTOM IC
(IC1010)) is passed through the LPF (inside the AF CUS-
TOM IC (IC1010)), and then applied to the D/A converter
(inside the AF CUSTOM IC (IC1010)) which adjusts its level
(=deviation).
The level-adjusted modulation signal is applied to the modu-
lation circuit.
• TX AF CIRCUITS
IC53
J1
IC7
MIC
[MIC
AMP
GAIN
JACK]
SW
FRONT UNIT
J1003
5 - 2
IC1010
SQIN
BUFF
BEEP
AFVO
BUFF
DAFO
REF
VCON
BUFF
BAL
MOD DMO
LPF
LINEAR
HPF LIMIT
AMP
CODEC
MOD
MICI ALC TX/RX
AMP
LINE
SW
AMP
CTRL
IC2007
DSP