Transmitter Circuits - Icom IC-F3001 Service Manual

RX AF CIRCUITS
The demodulated AF signal from the IF demodulator
IC is passed through the LPF, HPF which attenuates
frequencies 300 Hz and below. The filtered AF signal is
passed through the AF line SW, HPF which additionally
attenuates frequencies 300 Hz and below, de-emphasis
circuit which provides –6 dB/oct of frequency response.
The de-emphasized AF signal is passed through the AF
SW, LPF which attenuates frequencies 3 kHz and above, is
adjusted in level by the D/A converter. The level-adjusted AF
signal is then applied to the AF power AMP via the AF line
SW.
The amplified AF signal is applied to the internal or external
speaker.
• RX AF CIRCUITS
IC59
LPF
the demodulator
circuits
LPF
IC58
AF line SW
IC57
IC56
R2A20178
CD4066
D/A
converter
RMUT 1
IC58 IC62
RX
HPF
MUTE
IC58
HPF
IC55 TPA0211DGN
J52
Ext.speaker
AF
AFO
AM P
IC12
J53
TA7368F
1
AF
2
AM P
AFON
Int.speaker

4-2 TRANSMITTER CIRCUITS

TX AF CIRCUITS
The audio signal from the internal or external microphone
(MIC signal) is passed through the MIC gain SW and applied
to the MIC AMP. The amplified MIC signal is passed through
the MIC mute SW, HPF which attenuates frequencies
300 Hz and below. The filtered MIC signal is passed through
the pre-emphasis circuit which provides +6 dB/oct of
frequency response, then they applied to the limiter AMP.
The amplitude-limited MIC signal is passed through the
MIC line SW, and applied to the splatter filter, which
attenuate harmonics in the MIC signal to prevent exceeding
permissible deviation.
The filtered MIC signal is applied to the D/A converter which
adjusts its level (=deviation). The level-adjusted MIC signal
is applied to the TX VCO as the modulation signal.
• TX AF CIRCUITS
IC58
IC56
D/A
IC57
LPF
Splatter
MIC
line
SW
SP1
MODULATION CIRCUIT
The modulation signal from the TX AF circuits is applied to
D15 of the TX VCO to frequency-modulate it. The frequency-
modulated signal from the TX VCO is buffer-amplified by
two buffers, and applied to the TX AMP circuits via the TX/
RX SW (D5).
• MODULATION CIRCUITS
Q10
TX VCO
Q14,D16 BUFF
D15
FREQUENCY
MODULATION
From the TX AF circuits
4 - 2
IC58
IC62
IC58 IC60
MIC MIC
limit
HPF
AM P AM P
MUTE
MOD
To the modulation circuits
D5,D6
Q8
To the TX AMP circuits
LO
BUFF
SW
J51
Ext.MIC
IC62
MIC
GAIN
SW
MC51
Int.MIC