4 - 3
4-1-10 UHF RF CIRCUIT
The UHF RF signals are passed through part of a duplexer
(high-pass filter; L44, L45, L82, C189, C190, C493). The sig-
nals are then passed through the low-pass filter (L42, L43,
C187, C463), antenna switching circuit (D37, D39, D72), and
then amplified at the RF amplifier (Q44). A bandpass filter
(FI3) is used at the next stage of the RF amplifier. The RF
switch (D35, D33) turns on the UHF RF circuit when UHF sig-
nals are received.
4-1-11 UHF 1ST MIXER AND 1ST IF CIRCUITS
The filtered signals from the bandpass filter (FI3) are applied
to the 1st mixer circuit (Q43). The applied signals are mixed
with a 1st LO signal which comes from the U-VCO circuit
(Q20, Q21) to produce a 46.05 MHz 1st IF signal.
The 1st IF signal passes through the 1st IF filter (FI2) to sup-
press out-of-band signals via a matching circuit (R149,
C226). The filtered signal is amplified at the 1st IF amplifier
(Q41) and is then applied to the 2nd mixer circuit (IC8).
4-1-12 UHF 2ND IF AND DEMODULATOR CIRCUITS
The 1st IF signal from the IF amplifier is applied to the 2nd
mixer section of the FM IF IC (IC8, pin 16). The signal is
mixed for producing a 450 kHz 2nd IF signal with a 45.6 MHz
2nd LO signal whitch generated by the tripler circuit (L68,
L69, C208–C212) using the PLL reference frequency.
The 2nd IF signal from IC8 (pin 3) is passed through the 2nd
IF filter (FI6), and is then applied to the limiter amplifier sec-
tion in IC8 (pin 5). The signal is applied to the FM detector
section in IC8 to demodulate into AF signals.
4-1-13 UHF AF AMPLIFIER CIRCUIT
AF signals from IC8 (pin 9) pass through the AF selector
(IC21, pins 3, 4), low-pass filter (Q85, R381–R384,
C415–C418) and high-pass filter (Q86, R386–R390,
C419–C421).
The filtered signals pass through the volume control IC
(IC10). And the level adjusted signals are applied to the AF
power amplifier (IC12, pin 5) via the U-AF mute switch (Q71).
The output signal from IC12 (pin 7) drives the external speak-
er (connected at J2), or it is fed back to the input line of the
AF power amplifier (IC12, pin 2: VHF AF line).
4-1-14 UHF SQUELCH CIRCUIT
A portion of the AF signals from the FM IF IC (IC8, pin 9) are
applied to the active filter section (IC8, pin 8, 7). The active
filter section amplifies and filters noise components. The fil-
ered signals are applied to the noise detector section. The
variable resister (R229) adjusts the input level of the active
filter, and the level is used for squelch threshold reference.
The detected noise signals are output from pin 14 as the
“USQL” signal, and are then applied to the CPU (IC19, pin
95).
The [SQL] (CONTROL unit; R148) controls the input level of
the sub-CPU (CONTROL unit; IC10, pin 61) in DC voltage.
The sub-CPU reads the angle of the [SQL] rotation, then
send the squelch data to the CPU incorporated in the RDATA
line. Then the CPU controls U-AF mute switch (Q71) via the
“UAMUTE” line.
4-2 TRANSMITTER CIRCUITS
4-2-1 MICROPHONE AMPLIFIER CIRCUIT
The microphone amplifier circuit amplifies audio signals from
the microphone to a level needed at the modulation circuit.
The microphone amplifier circuit is commonly used for both
the VHF and UHF bands.
The AF signals from the microphone pass through the MIC
sensitivity control circuit (IC25, D66) and MIC mute switch
(IC26), and are then amplified at the microphone amplifier
(Q88). The amplified signals are applied to the IDC limiter
amplifier (IC23b, pin 6). The output signals from the IDC lim-
iter amplifier (IC23b, pin 7) are passed through the splatter
filter (IC23a, pin 3, 1) and then applied to each VCO circuit
via the deviation adjustment pot.
4-2-2 VHF MODULATION CIRCUIT
The modulation circuit modulates the VCO oscillating signal
(RF signal) using the microphone audio signals.
The audio signals (MOD) from the splatter filter (IC23a)
change the reactance of D3 to modulate the oscillated signal
at the V-VCO circuit (Q4, Q5) after passing through the fre-
quency deviation control (R2). The modulated signals are
amplified at the buffer amplifiers (Q6, Q7), and are then
applied to the drive amplifier circuit via the T/R switching cir-
cuit (D4).
4-2-3 VHF DRIVE AMPLIFIER CIRCUIT
The drive amplifier circuit amplifies the VCO oscillating signal
to a level needed at the power amplifier.
The RF signals from the buffer amplifier (Q7) pass through
the low-pass filter (L5, C35, C36), T/R switch (D4) and atten-
uator (R33–R35). The Tx signal from the attenuator is ampli-
fied at the pre-drive (Q11) and drive (Q12, D5, D6) amplifiers
to obtain an approximate 400 mW signal level. The amplified
signal is then applied to the RF power amplifier (IC1).
4-2-4 VHF POWER AMPLIFIER CIRCUIT
The power amplifier circuit amplifies the driver signal to an
output power level.
IC1 is a power module which has amplification output capa-
bilities of about 70 W. The RF signal from the drive amplifier
(Q12) is applied to IC1 (pin 1).
The amplified signals from the power amplifier (IC1, pin 4)
pass through the APC detector (D7, D8), antenna switching
circuit (D9) and low-pass filter (L15, L16, L78, C70–C72),
and is then applied to the antenna connector.
Collector voltage for the driver (Q12) and control voltage for
the power amplifier (IC1, pin 2) are controlled by the APC cir-
cuit to protect the power module from a mismatched condi-
tion as well as to stabilize the output power.
