5 - 5
The IDC limits the level of the amplitude of MIC signals to prevent
over deviation. The limited MIC signals are output from pin 7 and
passed through the splatter filter (IC302, pins 8, 9).
The splatter filter suppresses 3 kHz and higher audio
components.
The filtered MIC signals are applied to the D/A converter (IC303,
pin 1) via the mode switch (IC304, pins 10, 11). The D/A converter
(IC303) adjusts the deviation according to “DATA” signal from the
CPU (IC1, pin 30).
The level adjusted MIC signals are output from pin 2 and then
applied to the modulation circuit (VCO UNIT; D55 or D100) to
modulate the VCO oscillating signal.
• MICROPHONE AMPLIFIER CIRCUIT
The AGC signal controls the bias of the IF amplifiers (MAIN UNIT;
Q100, Q103/Q200, Q202) and RF amplifiers (RF UNIT; Q200,
Q250, Q300, Q301, Q401, Q500, Q501, Q601/Q700, Q701,
Q450, Q651) according to the received signal strength to prevent
audio distortion and stabilize the demodulated AF signal level.
5-1-6 SQUELCH CIRCUITS (MAIN AND LOGIC
UNITS)
• NOISE SQUELCH
The noise squelch mutes the AF output signals when no RF
signals are received. By detecting noise components in the
demodulated AF signals, the squelch circuit toggles the AF power
amplifier ON and OFF.
A portion of the FM-demodulated AF signals from the IF IC (MAIN
UNIT; IC100/IC200 (A_BAND/B_BAND), pin 9) is passed through
the noise filter (MAIN UNIT; IC100/IC200, pins 7, 8, R109–R113,
C118–C122/R212–R216, C218–C222). The filtered noise signals
are then applied to the noise amplifier in the IF IC to be amplified
the noise components only.
The amplified noise components are converted into the pulse-
type signal at the noise detector section, and output from pin 13
as the noise signal (A_BAND: “ANOIS”/B_BAND: “BNOIS”). The
noise signal is applied to the CPU (LOGIC UNIT; IC1, pin 26/28),
then the CPU outputs “AFON” signal from pin 97 according to
the noise detection signal level to toggle the AF power amplifier
regulator (LOGIC UNIT; Q105, Q106) ON and OFF.
• TONE SQUELCH
The tone squelch detects the tone signal in the demodulated AF
signals, and opens the squelch only when matched subaudible
tone frequency is detected in the received signal.
While the tone squelch is in use, and the received signal contains
no sub-audible tone signal or mismatched tone frequency, the
tone squelch mutes the AF signals even if the noise squelch is
open.
A portion of the demodulated AF signals from the IF IC (MAIN
UNIT; IC100/IC200, pin 9) are passed through the two-staged
CTCSS/DTCS filter (MAIN UNIT; IC150/IC250, pins 3, 1 and pins
5, 7) via the mode switch (MAIN UNIT; IC500, pins 1, 2/10, 11)
to suppress unwanted voice signals. The filtered CTCSS/DTCS
signals (A_BAND: “ATONE”/B_BAND: “BTONE”) are applied
to the CPU (LOGIC UNIT; IC1, pin 49/45) via the tone selector
(MAIN UNIT; IC703, pins 3, 4/10, 11).
The CPU decodes the CTCSS/DTCS signal, and outputs “AFON”
signal from pin 97 according to the set CTCSS/DTCS signal to
toggle the AF power regulator (LOGIC UNIT; Q105, Q106) ON
and OFF.
5-2 TRANSMITTER CIRCUITS
5-2-1 MICROPHONE AMPLIFIER CIRCUIT
(LOGIC UNIT)
The microphone amplifier circuit contains AF amplifier, IDC,
splatter filter, etc. The AF signals from the microphone (thereafter,
it is called “MIC signals”) are filtered and level-adjusted at this
circuit.
MIC signals from the microphone (MC300) are applied to the MIC
amplifier (Q302), then the amplified MIC signals are applied to
the mode switch (IC301, pin 1). In FM mode, the MIC signals are
output from pin 6 and applied to the IDC (Instantaneous Deviation
Control; IC302, pin 5).
In DV mode
†
, the MIC signals are output from pin 7 and applied to
the IDC (IC302, pin 5) via the ALC amplifier (IC300, pins 3, 5).
IC302
IC301
Microphone Q302
1
7
3 5
6
7
8
5
Mode
switch
to the
VCO
IDC
SPLATTER
MIC
1 2
D/A
converter
9
IC300
ALC
IC304
11 10
IC303
DV mode* onry
5-2-2 MODULATION CIRCUIT (VCO UNIT)
The modulation circuit modulates the VCO oscillating signal with
the AF signals from the microphone and the tone signals from the
CPU.
• MICROPHONE SIGNALS
The level adjusted MIC signals from the D/A converter (LOGIC
UNIT; IC303, pin 2) are applied to the D55 (in transmitting on 144
MHz band) or D100 (in transmitting on 430 MHz band) to modulate
the VCO oscillating signal by changing the reactance of D55 or
D100. The modulated VCO output signal is buffer-amplified by
Q200 and Q201, then applied to the transmit amplifiers via TX/RX
switch (RF UNIT; D100) and amplifier (RF UNIT; IC100, pins 1, 4),
as a transmit signal.
• TONE SIGNALS
The CTCSS and DTCS signals are generated by the CPU (LOGIC
UNIT; IC1) and output from pin 43.
The CTCSS/DTCS signals are passed through the tone filter
(Q307, R338–R340, C339, C340). The filtered tone signals are
mixed with the MIC signal coving from the IDC amplifier (LOGIC
UNIT; IC302 pin 7), then applied to the modulation circuit via the
the splatter filter, mode switch and D/A converter.
The CTCSS/DTCS signals are passed through the tone filter
(Q307, R338–R340, C339, C340). The filtered tone signals are
mixed with the MIC signals come from the IDC amplifier (LOGIC
UNIT; IC302, pin 7), then applied to the modulation circuit (D55
or D100) via the splatter filter (LOGIC UNIT; IC302, pins 9, 8),
mode switch (LOGIC UNIT; IC304, pins 11, 10) and D/A converter
(LOGIC UNIT; IC303, pins 4, 3).
5-2-3 TRANSMIT AMPLIFIERS (RF UNIT)
The VCO output signal is amplified to transmit output power level
by the transmit amplifiers.
The VCO output signal from the amplifier (IC100) is applied to the
pre-driver (Q102), driver (Q101) and power (Q100) amplifiers in
sequence to be amplified to the transmit output power level. The
power amplified transmit signal is passed through the antenna
switching circuit and transmit filters.
†
Available when the optional UT-121 is installed.
