Yaesu FT-902DM, Instruction Manual

Page: 32 / 55

The VOX GAIN con trol · YR ,
o n
the fron t pane l
p rovides adju stment for relay sensi tivity , a nd
V R60 1 con trols anti trip sensi tivity. R e lay hold
time is determined by delay con trol V R 6 0 2 .
The tone oscillator Q6 1 5( 2SC1 8 15GR) opera tes when
the MODE swi tch is in the
CW
posi tion . I t is a
phase shift oscillator opera ting a t approximately
8 00 Hz . The sidetone level is adj usted by V R6 0 3 .
The sideton e output is also coupled to the VOX
c ircuit for semi-b reak-in operation.
Located on the VOX UNIT, the crystal marke r
generator
Q
6 1
1 ( 2SC 1 8 1 S Y )
generates a basic 3 2 00
kHz crystal controlled signal which is divide d in t o
I
00 k H z mu ltiples b y frequency divid e r Q6 1 2
( 4 024PC ) .
The vol tage regulator
Q
6
0
5
( 2 SC
1 8 1 5Y )
regulates the supply voltage t o the
VOX
circuit.
FM UNIT (PB- l 7 07B )
The speech signal from pin 20 of P B- l 7 0 7 B is fed
t o amplifier limi ter Q 9 0 9
( TA706 1 AP ) ,
which clips
b o th p ositive and negative peaks when the y e x ­
ceed the level set for maximum devia tion of the
t ransmit ter frequency . Q9 1 0
( 2SC 1 8 1 5 Y )
acts as
I
"""�
an active low pass fil ter to eliminate harm onics
caused b y the clipping. VR90 2 de termines the
m aximum deviation .
The output from Q90 1 1s amplified by Q
9
1
1
( 2 SK34E)
and then fed to the modulator 0 9 0 9
( FC63 ) . Q9 1 2 ( 2
S
C 1 8 1
5 Y
)
oscillates a t a cry stal
freque ncy of 8 9 8 7 .5 kHz and is frequency m od­
ulated by varactor diode 0 9 0 9 . The outpu t from
Q9 1 2 is amplified by Q9 1 3 ( 2 SC 1 8 1 5Y ) and then
fed
to the NB UNIT.
TUNE UNIT ( PB - l 7 20 B )
When TUNE swi tch
S 2 1 0 1
is pushed , the vol tage
across C 2 1 0 1 is applied to the base o f
Q2 1 0 1
( 2
S
C I 8 1 S Y ) ,
causing
Q2 1 0 1
to turn ON ; this
activa tes
RL2 1 0 2
which grounds the cathodes of
D 2 1 o s
an d
D 2 1 0 6
(both 1 S 1 5 5 5 ) . As
0 2 1 0 5
is
connected in parallel with the PTT swi tch , the
transceiver is placed in th e transmit m ode.
Diod e 0
2 1 0
6 grounds the common terminal o f
t h e M O D E swi tch
S 2
g a n d
S 2
h , a n d the bias
vol t age o f the PA stage is l owered from the cut­
o ff condi tion to the normal operating leve l .
RIJ 22K
R L I
12V
TUNE , CW KEY ING C I RC U I T
-30-