cw
In th e CW,
AM ,
and FSK modes, carrier oscillator
Q702
( 2SK 1 9G R )
on the
CARR
UNIT generates
a crystal controlled carrier signal of
8988.2
kHz .
The carrier is fed through buffer amplifier
Q10 3
(2SC 1 81 5 Y )
to the ring modulator.
Q 7 0 2
also
oscillates
for
TUN E operation .
DC
voltage is applied through diode switch
09 1 2
(1 S l 5 5 5 )
and
RL70 1 ,
to unbalance the ring mod
ula tor for CW,
AM ,
and FSK operation ; the
resul ting carrier signal is fed to T
7 0 1
.
The outpu t from
T 7 0 1
is amplified by
Q 1 0 4
(3 SK59Y )
and fed to
Q2 0 1
( 2 SC 1 81 5 Y )
on the
NB
UNIT. The signal is th en furth er amplified
by
Q 2 0 3
( 3 SK 5 9G R ) ,
and is fed to th e transmitter
m ixer.
K eying of th e transmitter is accomplished by
changing the bias voltage to
V 1 6 0 1 , V 1 7 0 1
, and
V
1
1
0 2
.
The tubes are cut o ff on "key up" by
application of
- 3 5 V
for
V 1 6 0 1
and
- 1
l
O
V
for
V
1 7 0 1
and
V
1 102 .
These cutoff voltage are re
duced to
-- 0. 1
V
and
-
60
V
, respectively , during
"key
d own" conditions.
The key is connected to pin!
3
of the
REC C
U NIT
(PB 1 7 1 7A ) .
Under "key d own" conditions, the
base o f
Q 1 8 0 3
( 2 SA 733)
is grounded, causing
Q 1 8 0 5
(2SC 1 81 5GR)
and
Q 1 8 0 4
( 2 SA639)
to
con duct. The voltage at pin
1 6
of
PB- 1 7 1 7
A
reaches
zero
when
Q 1 8 0 4
conducts. Since pin
1 6
o f
PB-
Keyer speed is controlled by
VR2
b on the fron t
panel.
VR2 7 0 1
provides adjustment o f the dot
space symme try, while
VR2 7 0 2
adjusts th e keying
weigh t .
VR2 7 0 2
normally i s s e t to minimum,
providing a
1 : 1
d ot : space weight.
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Th e microph one signal is amplified by
Q1 o s
(TA7063P)
and
Q7
1
0
(2SC 73 2T M )
and fed tq
Q704
( 3S K 5 9Y ) ,
where it modulates the
8988. 2
kHz carrier signal. The output from T
7 0 2
is fed
to the NB U NIT in the same manner as described
in the CW section previously.
1 7 1 7
A
is connected to pin
2
o f th e
RECT A
UNIT
FSK
(PB- 1 7 08) ,
the bias vol tage of
V 1 6 0 1 , .Y 1 7 0 1 ,
and
V
1 7 0 2
places these tubes in the normal operating
c ondition .
On other modes,
1 2
volts is applied to pin 1 5 ,
causing
Q 1 8 0 4
to c onduct, th us placing th e operat
in g bias on the tubes.
KEYER UNIT
(PB- 1 7 28A)
The built-in electronic keyer utilizes
02 7 0 1
(Curtis
804 4 IC).
The output of
02 7 0 1
is high during
"key down" c on ditions ; th is output is connected
to the base o f
Q 2 7 0 2
( 2S C 1 81 5 Y ) ,
the collector
current of which is c onnected to th e base of
Q
1 8 0 3 ,
causing
Q 1 8 0 3
to c onduct during "key
d own" conditions.
The carrier oscillator
Q7 0 2
( 2S K 1 9GR )
generates
a crystal controlled carrier frequency of
8988. 2
kHz . When keying is applied to th e F S K jack J
1 5 ,
th e b ase voltage of
Q7 0 1
( 2SC 1 81 5Y)
becomes
zero , c au sing
Q7 0 1
to cut off. In the "space"
c ondition ,
Q7 0 1
conducts, placing TC7 0 4 in the
circuit and l owering the carrier frequency to
8988.03
kHz .
AMGC
circuit
Th e
AM
.
GC
circuit is l oc ated in tl-ie
CARRIER
U NIT and is used to reduce. th e gain of th e micro
ph one amplifier when only low-level b ackground
noise is present (no speech input fr om the opera-
-28-
Содержание FT-902DM
Страница 1: ...INSTRUCTION MANUAL FT 902DM YAESU MUSEN CO LTD TOKYO JAPAN ...
Страница 54: ...YA E SU v 8103 A ...
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