Kat-2 (Internal Automatic Antenna Tuner); External View; Auto Antenna Tuner Block Diagram - Kenwood TK-80 Service Manual

TK-80

KAT-2 (Internal Automatic Antenna Tuner)

External View

Circuit Description
1. Auto antenna tuner
When the AT TUNE switch is pressed, ATA goes high.
AUTO/THRU switching relay K1 closes, and the AT is in-
serted. The CW mode is entered, and the transmission out-
put becomes about 10W. If the VSWR is less than 1.1, tun-
ing is regarded as complete, and the AT TUNE operation
stops. If the VSWR is greater than 1.1, the duty cycle of the
motor control pulse (described later) is controlled according
to the VSWR. If tuning is not complete after more than 20
seconds, AT TUNE operation stops at below VSWR 1.3.
The motor speed is determined by the microprocessor,
and the direction is determined by the phase comparator IC1
and amplitude comparator IC6 if the APRE is low, and by the
microprocessor if the APRE is high (Fig. 1).
Forward wave/
IN Reflected wave
92
AT UNIT
L1,2
AT1
Detector
Phase Difference/
Amplitude Difference
IC1,6
Fig. 1 Auto antenna tuner block diagram
2. Auto tuning
The transmitter power from the final unit passes through
current/voltage detection transformers L1 and L2, which
have toroidal cores. The current and voltage components
detected here are rectified by a waveform rectification circuit
consisting of D3 to D5, Q1, D6 to D8, and Q2, and are then
phase-compared by IC1. The output signals (Q and Q) from
pins 5 and 6 of IC1 passes from IC2 through the switch, and
are applied to the motor drive IC, IC4. Variable capacitor
VC101 is turned by motor M1 so that the phase difference of
the voltage and current components decreases.
The voltage and current components detected by L1 and
L2 are rectified by diode's D1 and D2, and are applied to volt-
age comparison circuit IC6 as the amplitude component of
the signal. The comparator output passes from IC3 through
the switch. Motor M2 is driven by another motor drive IC,
IC5, which turns variable capacitor VC102 in the direction that
decreases the amplitude difference of the voltage and cur-
rent components.
Thus, variable capacitor VC101 adjusts the capacitance of
the circuit so that the current and voltage phases match, and
variable capacitor VC102 adjusts the resistance of the circuit
so that the current and voltage amplitude difference de-
creases. If the phases match and the amplitude difference is
zero, the VSWR is 1.0.
The speed of motors M1 and M2 is determined by the
duty cycle of the pulse input to pin 8 of IC4 and IC5. It is
controlled according to the VSWR calculated by the CPU in
the control unit and the speed corresponding to preset or
manual antenna tuning.
Pulse signal SPED from the control unit passes through
Q5, and is amplified by Q4 to produce a control pulse input to
IC4 and IC5.
V/A
Detector
IC2,3
Detector
PORT
VSF
VSR A/D
CONTROL UNIT
FINAL UNIT
AT2
Matching
Circuit
VR101
VR102
Motor
Driver
IC4,5
PORT A/D
CPU
OUT