TK-90
26
The signal passed through the IF amplifier loses all unnec-
essary signals other than the second IF signal at the MCF
(XF101). Here, it is inserted into the second transmission
mixer (IC101) and is converted to the transmission frequency
signal.
The signal from the second transmission mixer (IC101)
passes through the receiving circuit BPF, becomes amplified
at the drive amplifier (Q3), and is sent from CN1 to the Final
unit.
CIRCUIT DESCRIPTION /
!
73.095MHz
XF101
RF BPF
1.605~30MHz
TX signal
Q186
Q187
D183
ALC
Q182
TGC
10.695MHz
TX signal
LO2
62.4MHz
IC101
Q3
LO1
■
Control Circuit
1) ALC Circuit
This is the feedback loop circuit for avoiding raising of the
transmission power above the specified value. It monitors
the forward wave detection voltage (VSF) detected at the fi-
nal unit, lowers the first IF amplifier gain so as not to exceed
the specified value, and controls the antenna end transmis-
sion power.
The VSF voltage is added to the base of Q363 and the
POC voltage (Power Control Voltage) is added to the emitter.
If the VSF voltage generated by the transmit power becomes
POC + approximately 0.7V, the Q363 collector current runs
and the collector voltage decreases from 5.6V. Q365, D370,
Q366, and D372 convert the voltage change to the correct
control voltage, change the first IF amplifier Q186 second
gate bias, and control it so that the transmit power is not over
the specified value.
2) Power Control Circuit
By lowering the ALC circuit POC voltage, the VSF voltage
where ALC starts being active becomes lowered. By doing
this, the transmission power can be lowered as well. How-
ever, in this condition, the ALC starts becoming active when
the microphone input level is low.
Therefore, the IF amplifier (Q186) gain should be lowered
in accordance with the POC. By making the ALC voltage de-
fault value (the voltage when transmitting no signal) variable
depending on the set transmission power, the IF amplifier
(Q186) gain is changed at the same time.
■
From Drive Output to Antenna
The transmission signal sent from CN2 of the TX-RX unit
(X57-721) to CN2 of the Final unit (X45-378) is amplified for its
power by the pre-drive amplifier (Q1), the drive amplifier (Q2
and Q3), and the final amplifier (Q4 and Q5). The higher har-
monic wave is then removed with a LPF of the specified fre-
quency band, and the transmission signal passes through
traveling wave, reflecting wave detection circuit, and trans-
mission/receive switching relay and is sent to the antenna
terminal.
j`c=EucNMNF=
!"#$%&'()*+,-"#(
!"#$%&'()*+,-./01234
=Ef`NMNF
!"#$%&"#'()*
!"#$
=Ef`NMNF=
!"#$%&
_mc
!"
!
=EnPF=
!"#$
`kN
cáå~ä
Fig. 10
From modulation circuit to drive output /
NM
!"#$%&'
!"
NF=^i`
!"#$ %&'()*+,-./0123 4
!"#$%&'()*+%&,-
=EspcF
!"#$
!"#$%&'()*+,-./01234
spc
!"
nPSP
!"
ml`
=E
!"#
F
!"#$%&'!"()*+,
spc
!
ml`= H
MKTs
!
nPSP
!"#$% !&'
RKSs
nPSR
aPTM
nPSS
aPTO
!"#$%&'() *
!"#$%&
nNUS
!"#$%&'()*+,-
!"#$%&
=
OF=
!"#
!
^i`
ml`
^i`
!"#
spc
!"# $%&'()*!+,-./0123456
^i`
!"
!"#
ml`
!"#$
=EnNUSF=
!"#$%
!"#$
^i`
!"
=E
!"#$%&'
F=
!"#$%&'()*
=EnNUSF=
!"#$%&
quJou
=EuRTJTONF=`kO
cáå~ä
=EuQRJPTUF
`kO
!"#$%&'()*+
=EnNF
!"#
=EnO
nPF=
!"#$
=EnQ
nRF=
!"#$%&'()*+
imc
!"#$%&'()*+,-.$/0'$1
!"#$
L
!"#$%&'()*+,-
=
