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The output signal from the CW break-in circuit is also
applied to the CW side-tone generator circuit (Q80, Q81).
4·2·4 TRANSMIT IF AMPLIFIER CIRCUIT
(MAIN UNIT)
The modulated IF signal from a modulation circuit is applied
to the IF amplifier circuit (Q1). The amplified IF signal is
then applied to the RF-A (during VHF) or RF-B (during
UHF) unit via the V/U switching circuit (018).
The gain of the IF amplifier circuit (Q1) is controlled by the
ALC amplifier circuit (IC3a). Therefore, the IF amplifier is
reduced when the output power increases.
4-2-5 RF CIRCUIT (RF-A AND RF-B UNITS)
The RF circuit consists of mixer and drive amplifiers to
obtain the desired frequency and level needed at a PA unit,
respectively.
(1) VHF band (RF·A unit)
The IF signal is mixed with an LO signal from the VHF VCO
circuit (PLL unit, 01, 01-03, 08) at the double-balanced
mixer circuit (01, 02) to be converted into a VHF transmit
frequency. The mixed signal is then passed through the
tunable bandpass filter (03-05) to suppress spurious com-
ponents, and then amplified at the drive amplifiers (IC1, Q4,
013) to obtain an approx. 800 mW output level.
The amplified RF signal is applied to the PA-A unit via J7.
(2) UHF band (RF·B unit)
The IF signal is mixed with a 2nd LO signal at the double-
balanced mixer circuit (01, 02) to produce a 2nd IF signal
(71.25 MHz).
The 2nd LO signal is generated at the
reference oscillator and multiplier circuit (PLL unit, X1, Q14)
via LO amplifier (IC2). The 2nd IF signal is amplified at the
buffer amplifier (03) via the bandpass filter circuit (L3, L4,
C12-C14, C164. C178, C179). The amplified 2nd IF signal
is applied to the
1
st mixer circuit (IC3).
The 1 st mixer circuit converts the 2nd IF signal into a UHF
transmit frequency with a
1
st LO Signal from the UHF VCO
circuit (PLL unit. as, 04. 010). The converted RF signal is
amplified at drive amplifiers (IC1. 04, aS) to obtain an
approx. 200 mW output level. The signal is then applied to
the PA-B unit via J3 .
• APC and ALC circuits
..
I
Bandpass filters (L36, L37) are designed between drive
amplifiers to suppress spurious components in the RF
signal.
4-2-6 POWER AMPLIFIER CIRCUIT
(PA-A AND PA·B UNITS)
The power amplifier circuit amplifies the RF signals to the
specified output power.
(1) VHF power amplifier circuit (PA-A unit)
The RF signal from the RF-A unit is applied to the power
amplifier circuit (IC2). The amplified RF signal is applied to
the antenna connector (J2) via the power detector (04-07,
L8), antenna switching (01-03) and low-pass filter (L3-L5,
C5-C8) circuits.
(2) UHF power amplifier circuit (PA·B unit)
The RF signal from the RF-B unit is applied to the drive
amplifier circuit (IC3) to obtain 4-5 W output level and then
applied to the power amplifier circuit (IC1). The amplified
RF signal is applied to the antenna connector (J1) via the
power detector (04, OS, L9), antenna switching (01-03)
and low-pass filter (L3-L5, C5-C10) circuits.
4-2-7 ALC CIRCUIT
(PA-A, PA-B AND MAIN UNITS)
The ALC (Automatic Level Control) circuit protects the
power module (PA-A unit, IC2 for VHF and PA-B unit. IC1
for UHF) from a mismatched output load. Also, the ALC
circuit controls the gain of the transmit IF amplifier in order
for the transceiver to output a constant RF power set by the
[RF PWRl control even when the supplied voltage shifts,
etc.
The RF power level is detected at the power detector circuit
(PA-A unit, 04-07, L8 for VHF, PA-B unit 04. OS, L9 for
UHF) to be converted into OC voltages.
The detected
voltage (FORA for VHF or FORB for UHF) is applied to the
difference amplifier (MAIN unit, IC3a). A reference voltage
(POCO) for IC3a is controlled by the [RF PWRl control to
output difference voltages. The output voltage is applied to
the transmit IF amplifier circuit (MAIN unit, Q1) as an AALC
Signal to control the amplifier gain.
to antenna connector
IF
signal
I
APC~""""
.........•....... :
I
det.
i
i
I
iDS
04:
I
:
:
I
I' -
0::-
:Current:
I
'0::
' :
OS:
I
RF·A unit
I
~
......••.•••.
.idet.
_ ..•••......................
-MAIN-
u-;"ii -
-'C4b - -
~
- - - - -
-!
<
'--_ _ _ _
--1~7<
APC
HVF
.
~
PA-A unit
!-------------IC1-f~~
PA.S - - - - - -
-u.. - - - - - - - -
I - - - - - - - - - - - - + - -
FORB from PA·B
1'----"1'111<::-1
[RF PWRl
control
4-5
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