TK-90
27
The idling current adjusting trimmer potentiometer is ad-
justed as VR1 for the pre-drive, VR2 for drive Q2, VR3 for
drive Q3, and the final steps Q4 and Q5 are adjusted to VR4.
Although a FET is used for the drive amplifier, because the
FET’s Vth characteristics vary greatly, the drive step idling
current is adjusted separately for Q2 and Q3. Please note
that the same hfe rank transistor is used for the final steps,
Q4 and Q5.
The LPF circuit of this transceiver divides the frequency
band of 1.605~30MHz into 7 (6 in previous models), and en-
sures a higher harmonic wave attenuation within the band
range.
Thermistor (TH1 and TH2) for temperature protection de-
tection converts temperature change to voltage, is output
from CN4’s TH1 and TH2 terminals to the TX-RX unit, and
controls the fan motor and power down.
In transmit power detection, the voltage at coil L8 is de-
tected at D7 for traveling wave and D6 for reflecting wave,
output from CN4 to the TX-RX unit as VSF and VSR signals,
and is used for transmission output control. The current run-
ning in the drive circuit is detected at R1 as ID+ and ID–, and
the current running in the final step circuit is detected at R3
as IC+ and IC–. Each signal goes from CN4 to the TX-RX unit
and is used for transmission output control.
For the pre-drive for excess current protection, chip fuse
F1 (5A) for the drive circuit, chip fuse F2 (10A) for the power
switch Q7 protection, and blade-type fuse F3 (4A) for the ex-
ternal antenna tuner power are used.
The DC power supply coming in from the power connec-
tor into the transceiver is divided into 2 lines of 14V and 14S.
A 14V power supply which does not go through the main
power switch FET (Q7) is added to the final step transistor Q4
and Q5’s power supply and from CN3 to the MCU in the TX-
RX unit.
The main power switch FET (Q7) is controlled by Q8 and is
turned ON/OFF. The PSC signal from the TX-RX unit is ap-
plied to Q8, and when the PSC signal is High, Q7 is ON and a
current of approximately 5A goes through Q7.
Power supply 14S, which went through Q7, becomes the
power supply for the pre-drive and drive. 14S becomes an 8V
power supply of 8A at IC2, and is used for the final transistor
base bias. 8A is supplied from CN3 to the TX-RX unit. 14S
becomes an 8V power supply of 8D at IC1, and the power
supply 14AF which came through the choke coil L29, from
CN3 to the TX-RX unit.
For the relay for LPF (K101~K702), the controlling IC (IC3),
FEN, CLK, and DAT control signals from the TX-RX unit come
through CN4. IC3’s 5V power supply is also generated at the
TX-RX unit and is supplied from CN4’s 5A terminal.
CIRCUIT DESCRIPTION /
!
ANT
Q2
Q1
Q3
Q4
Q5
DRV IN
TX LPF
1.605~30MHz
band
L8
SWR
VSF VSR
K1
RAT
(TX-RX unit)
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