Kenwood TK-3360 Service Manual page 10

TK-3360
3-3. IF Amplifi er Circuit
The fi rst IF signal is passed through a four-pole mono-
lithic crystal fi lter (XF401) to remove the adjacent channel
signal. The fi ltered fi rst IF signal is amplifi ed by the fi rst IF
amplifier (Q405) and is then applied to the IF system IC
(IC401).
The IF system IC provides a second mixer, limiting ampli-
fi er, quadrature detector and RSSI (Received Signal Strength
Indicator). The second mixer mixes the fi rst IF signal with
the 50.4MHz signal of the second local oscillator output
(Q403) and produces the second IF signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
(Wide: CF402, Narrow: CF401) to remove the adjacent chan-
nel signal. The fi ltered second IF signal is amplifi ed by the
limiting amplifi er and demodulated by the quadrature detec-
tor with the ceramic discriminator (CD401). The demodu-
lated signal is routed to the audio circuit.
3-4. Wide/Narrow Switching Circuit
Wide and Narrow settings can be made for each channel
by switching the ceramic fi lters CF402 (Wide), CF401 (Nar-
row). The Wide and Narrow switching data is output from
IC809.
D401 and D402 are switched to ceramic fi lters when a
Wide/Narrow level is selected.
IC401
Narrow
Fig. 3 Wide/Narrow switching circuit
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CIRCUIT DESCRIPTION
R424
CD401
R426
50C
AFOUT
Wide
CF402
D401 D402
CF401
3-5. Audio Amplifi er Circuit
The demodulated signal from IC401 is sent to an AF am-
plifi er through IC812, and is routed to an audio power ampli-
fi er (IC815) where it is amplifi ed and output to the speaker.
3-6. Squelch Circuit
Part of the AF signal from the IC401 enters the FM IC
(IC401) again, and the noise component is amplified and
rectifi ed by a fi lter and an amplifi er to produce a DC voltage
corresponding to the noise level.
The DC signal from the FM IC goes to the analog port of
the MCU (IC809). IC809 determines whether or not to out-
put sounds from the speaker by checking if the input volt-
age is higher or lower than the preset value.
To output sounds from the speaker, IC809 sends a high
signal to the AFSW line and turns IC815 on through Q813,
Q814, Q818 and Q819.
4. Transmitter System
4-1. Microphone Amplifi er Circuit
The signal from the microphone is limited by the AGC
circuit, which is composed of D807, 808, Q810, Q811 and
the mute switch (Q809). IC812 is composed of a high-pass
fi lter, low-pass fi lter and pre-emphasis/IDC circuit.
The signal from the microphone and the low speed data
from the MCU (IC809) enter the Audio processor IC (IC812)
and pass through each path and are mixed inside the IC.
The output signal from the audio processor goes to the
VCO modulation input. The other output signal goes to the
TCXO modulation input.
MIC
D807,808
AGC
Q810,811
MMUTE SW
Q809
Fig. 4 Microphone amplifi er circuit
IC812
VCO
Audio
processor X1
TCXO
LSD
OUT