Kenwood TS-440S Serivce Manual page 12

TS-440S
CIRCUIT DESCRIPTIO N
waves changing from continuous waves to relatively low dut y
pulses . Q1 is driven by this voltage waveform to control Q2 ,
which is connected to the collector of Q4 in series and mo-
tor drive voltage is generated .
If the motor turns too fast, the SWR value will be smalle r
than the motor stop value because of the inertia of the mo-
tor . As a result, the motor will continue to operate even if
the motor stop signal is sent and the SWR value will con-
tinue to be greater than the motor stop value, causing th e
motor stop signal to turn off . That is, the motor will not sto p
and it will be difficult to obtain a match . If the motor spee d
is too slow, it will take a long time to satisfy a matching con -
dition . The TS-440 therefore controls the motor speed ac -
cording to changes in SWR .
TUNE STO P
ADJ
IC8
c/4 Q 5
Triangular wov e
generator
Fig . 7 Antenna tuner circuit
The antenna coupler is a T type . Six relays RL100 to RL10 5
are used to change taps within the range 3 .5 MHz to 30 MHz .
2) Cooling fan circui t
The final unit contains the temperature-sensitive thermisto r
TH1 thermally coupled with final transistor Q4 . When tem-
perature on the surface of Q4 reaches approx . 50°C, the fa n
start comparator Q9B operates (H level), causing Q8 to tur n
on to operate the fan . During operation of the fan, tempera -
ture protection comparator Q9A is at a L level, so the tem-
perature protection circuit does not operate .
When temperature on the surface of Q4 goes down to 45°C ,
the cooling fan turns off .
• Final temperature protection circui t
When the temperature of the final transistor Q4 rises u p
to approx . 80°C, the temperature protection comparato r
Q9A turns on (H level), Q1 in the filter unit also turns on ,
and a minus DC voltage is supplied to the ALC line, reduc -
ing the transmitter output to zero . (The TS-440 does no t
return to a receive state .) When the temperature of th e
final transistor Q4 falls to approx . 70°C, the protectio n
circuits turns off allowing the transmitter to operate again .
• SWR protection circuit
When antenna VSWR is bad, or the reflected wave is to o
large, because the auto antenna is tuning for example, L4 2
and L43 detect the state and its output is rectified . Th e
rectified signal is then amplified by Q2 to control the AL C
voltage so that drive power is reduced . As a result, loa d
on the final unit is reduced .
• SWR automatic arithmetic circui t
The TS-440 uses the automatic arithmetic circuit in th e
AT-250 . The forward wave voltage
VSF
and reflecte d
wave voltage
VSR
from the filter unit are fed into the ana -
log arithmetic circuit of the switch unit, and used to se t
the voltage level of IC8 pin 2 (5 V +VsR/VSF) . Output vol-
tage from the pin 2 is shifted by IC5 to move the needl e
in the SWR meter .
IC5 contains a level shift/meter amplifier and an auto tune r
V-I convertor . IC7 contains a square wave generator an d
a voltage comparator . IC8 contains an integration circuit .
Q3 and Q4 are used to switch forward and reflected wav e
input signals alternately .
Comparato r
output
Q9 B
/45° /50°
0° Bo° Temperature ° C
FAN OFF FAN ON Thermal Therma l
protection OFF protection ON
Fig . 8 temperature protection operatio n
V
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