5 - 2
RX AF CIRCUITS
The demodulated AF signal from the linear codec (IC2006)
is amplified by the AF AMP (IC1007), and then adjusted in
level by the electronic volume (IC1006). The level-adjusted
AF signal is then amplifi ed by the pre-AMP (IC1004) and AF
power AMP (IC1009).
The amplified AF signal is passed through the external
speaker jack, and then applied to the internal speaker.
• RX AF CIRCUITS
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 emitted.
A portion of demodulated AF signal from the IF IC (IC4)
is passed through the D/A converter (IC1006) 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 the noise components (approx.
30 kHz signals) only. The noise components are rectified,
resulting in 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
AF
AMP
AF
AMP
IC1009
J1002
SP1
Int.speaker
Ext.speaker
From the linear codec
IC1004
AFO
DAFO
Electronic
volume
FRONT UNIT
IC1006
AMP
IC1007
DAC
Noise
AMP
Noise filter
From IF IC
(IC4, Pin16)
To RX AF circuits
Noise
detector
Com-
parator
NOISE SQUELCH DIAGRAM
“NOIS”
IC1006
IC4
14
8
7
13
15
J1
FRONT UNIT
[Option connector]
[MIC
JACK]
J1003
MIC
GAIN
SW
IC53
AMP
IC7
ALC
AMP
IC1005B
HPF
IC1005A
LIMIT
AMP
IC1007A
MIC
LINE
IC1008
SW
DMI
DSP
LINEAR
CODEC
IC2006
IC2007
LPF
IC1007B
MOD
DMO
D/A
IC1006
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 MIC
AMP (IC7).
• WHILE OPERATING IN THE ANALOG MODE
The amplified MIC signal is passed through the HPF
(IC1005A), which attenuates frequencies 300 Hz and below,
and then applied to the limiter AMP (IC1007).
The amplitude-
limited MIC signal is applied to the linear codec (IC2006)
through the MIC line SW (IC1008).
The MIC signal is converted into a digital audio signal by the
linear codec (IC2006), processed by the DSP (IC2007), and
then converted into an analog baseband signal (modulation
signal).
• WHILE OPERATING IN THE DIGITAL MODE
The amplified MIC signal is applied to the ALC (IC1005B)
which keeps the signal level fi xed.
The level-adjusted MIC signal is
applied to the linear codec
(IC2006) through the MIC line SW (IC1008).
The MIC signal is converted into a digital audio signal by the
linear codec (IC2006), processed by the DSP (IC2007), and
then converted into the digital baseband signal (modulation
signal).
The signal from the linear codec (
IC2006
) is passed through
the LPF (IC1007), and then applied to the D/A converter
(IC1006)
which adjusts its level (=deviation)
.
The level-adjusted modulation signal is applied to the modu-
lation circuit.
• TX AF CIRCUITS
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