Yaesu FT-902DM, Инструкция по эксплуатации

Страница: 29 / 55

TRANSMIT CIRCUIT
S S B
The ou tput from the M IC j ack J
2
is fed through
the MIC GAIN control VR 3 a to pin 1 3 of the
CARRIER UNIT.
CARRIER UNIT ( P B- 1 706A)
The microphone signal is amplified by microphone
amplifier
Q7 0 5 ( TA-7063 P )
and fed through relay
RL7 0 1 to the ring m odulator consisting o f
D 7 0 5 -
0 7 0 8
(all
1 S 1 00 7 ) ,
where the signal m odulates
carrier signal delivered from
Q7 0 3 ( 2 SC 1 8 1 S Y ) .
The d ouble sideband signal is fed through T
7 0 1
to the FILTER UNIT.
FILTE R U NIT ( P B- 1 99S )
The 8 9 8 7 .5 kHz signal fed to pin 8 of the FILTER
UNIT is amplified by buffer amplifier
Q 3 04
( 2 S K
1 9GR )
and is passed through sideband filter
X
F
3 0 4
by diode switches
D 3 0 9 ( l S l S S S )
and
D 3 0 7 - D 3 0 8
(both
1 S1007 )
where the D S B signal i s converted
to an S S B signal by removing the unwanted side­
band .
N B UNI T (P B- 1 994 )
The S S B signal is fed through a bu ffer amplifier
Q 2 0 4
(2SC 1 8 1 SY) to the bases of
Q 2 0 2
and Q2 0 5
(both 2SC 1 8 1 S Y ) . When the RF processor switch
is "OFF,'' the S S B signal is amplified by
Q 2 0 2
and fed t o
Q2 0 3
( 3 S KS 9G R ) . When the processor
switch is "ON ,'' the SSB signal is amplified by
Q 2 0 5
( 2 SC 1 8 1 S Y ) and is further amplified by
the limiter
Q2 0 6
(TA 7060P ), where the signal s
that ex ceed the p reset clipping . level are sliced out.
V R 2 0 3
is used to equalize the level of the clipped
and unclipped signals.
This highly clipped S SB signal is passed through
a selective fil ter
XF 2 0 1
to remove RF harm onics
that result from signal clipping. The filtered out­
put signal is amplified by
Q2 0 3
and fed to the
RF UNIT. The PROC LEVEL control
V R 5
b,
located on the front panel, varies the resistance
between the collector and emitter of
Q 2 0 7 ( 2 SC
181 S Y ) ,
thus changing the input sign al level to
the filter.
The CW, FSK, AM , and FM signals pass through
Q2 0 1 ( 2 S K1 9GR) and are fed to Q2 0 3 .
The A LC (Automatic Level Control ) v oltage
detected at the grid circuit of the PA tube is fed
to the first gate o f
Q2 0 3
to reduce the gain of the
amplifier, thus preventing overloading and dis­
tortion .
RF U NIT (P B-21S4 )
Th e S S B signal from J
1 0 2
o f the p rinted b o ard i s
fed to the diode rin g mixer
Q i o 2 ( N D4 8 7C2-3 R ) ,
where the S SB signal i s heterodyned t o t h e d esired
RF frequency by mixing with the l ocal signal
which is supplied from the VCO UNIT. The
mixer output is amp lified by
Q i o s
( 2 SC240S )
and
Q i 0 6
( 3 SK4 0M ) , and applied. throu gh diod e
switch D
l l
o ( 1 S 1 00 7 )
t o the D RIVE UNIT.
DRIVE UNIT ( P B-17 1 4 ) PA UNIT ( P B- l 7 1 S )
The output from the RF UNIT is fed to the grid
of the transmi tter driver
V 1 6 0 1 ( 1 2 BY7A)
where
it is amp lified to a level su fficient to drive the
final amp lifier tubes
V 1 7 0 1
and
V 1 7 0 2
( 61 46B) .
A p ortion of the RF signal is coupl e d through
C 1 6
to the cathod e of the 1 2BY7A driver tube
so as to imp rove the linearity of the final amplifier
stage ( R F negative feedback).
Neutralization o f the p ower amplifier is accom­
plished by feeding b ack a small amoun t of the
output through TC
1
to the cold end of the T
3
/L9
combination . The re turn of the grid circuit is
connected to the REC A UNIT
(P Bl 708) t o
produce ALC voltage to con trol the gain . o f the
TX IF amplifier, thus preventing distortion caused
by overdrive .
- 27-