Yaesu FT-901DM Instruction Manual page 32

The VOX GAIN control V R 1
provides adju stment for re lay
VR 6 0 1 c on trols anti trip sensi t i v i t y . Re lay hold
time is determined by delay con trol V R 6 0 2 .
The tone oscillator Q 6 1 5
the MODE swi tch is in the CW posi tion. It is a
phase shift oscillator operating at approxima tely
800 z The sidetone level is adju sted by V R 6 0 3 .
H
.
The side tone output is also coupled to the VOX
circuit for semi-break-in operation.
Located on the VOX UNIT, the cry s tal marker
generator Q 6 1 1 ( 2 SC 1 8 1 5 Y )
kHz cry stal controlled signal which is d ivided i n t o
1 00 k H z mu ltiple s by frequency divider Q 6 1 2
(4024PC ) . The v oltage
1 8 1 5 Y ) regulate s the su pply voltage to t
circuit.
FM UNIT (PB- 1 707 )
The speech signal from pin 20 of PB- 1 7 0 7 is fed
to amplifier limiter Q 9 0 9
bo th positive and negative pe aks when the y e x ­
ceed the level s e t for maximum deviation of the
transmitter frequency . Q9 1 0
T X 12V >--l- -'- -- -'
12V >--- --'
TX
on
the fron t p ane l
sensi tiv it y , and
( 2SC3 7 3 ) opera tes when
genera tes a basic 3 2 00
regulator Q 6 0 5 ( 2 SC
he
VOX
(TA706 1 AP ) , which clips
( 2SC 1 8 1 5 Y ) acts as
cw
12V >--+- -- -- -- -- -'i i
an active low pass filter to eliminate harm onics
c aused by the clipping. V R 9 0 2 de termines the
m aximum deviation .
The outpu t from Q 9 0 1
( 2 SK34E) a nd then fed t o the m odulator 0 9 0 9
( FC6 3 ) . Q9 1 2 ( 2 SC 1 8 1 SY )
freq u e n c y
o f 8987
ulated by varactor diode D 9 0 9 . The o u tput from
Q 9 1 2 is amplified by Q 9 1 3
fe d to the NB UNIT.
TUNE UNIT ( PB- 1 7 20 )
When TUNE swi tch S 2 1 0 1 is p ushe d , the v ol tage
across C2 1 0 1
is applied to the base of Q 2 1 0 1
( 2 SC 1 8 1 S Y ) , causing Q2 1 0 1
activates RL2 1 02 which grounds the cathodes o f
D 1 1 o s a n d D 2 1 0 6 ( b o t h
connected i n parallel with the PTT swi tch , the
tran sceiver is placed in the transmit m ode.
Diode D 2 1 0 6 grounds the common term i n al of
the MODE switch S 2 g and S 2 h , and the bias
vol t age of the PA stage is lowered from the c u t­
o ff con d i tion to the normal operating level.
- 3 0 -
is amplified by Q 9 1 1
a t
oscillates a cry stal
an d is frequency mod­
.5 kHz
( 2 SC 1 8 1 SY ) and then
to turn ON ; this
1 S l 5 5 5 ). A s D 2 1 0 5 is
TUNE , CW KEY ING C I RC U I T