Kenwood TS-440S Service Manual page 10

TS-440S
3. Transmitter Circuit Description
M I C
FSK IN
In S S B , CW, A M, o r FSK mode, t h e tra n smitter system uses
t rip l e conversio n . In F M mode, the tra n smitte r system uses
d o u b l e conversio n using PLL mod u l atio n .
A u dio sig n a l s from the mic ro p h o n e a re a p plie d t o t h e M IC
pin ( c o n n ector ( 2 1 )) of the IF u nit a n d a re separated into SS B
mod u l ation a n d VOX sig n a l s . The S S B sig n a l is amplified a p­
p rox . 8 d B by IC4 (µPC 1 1 5 8HZ) . AFSK a u dio sig n als from
the AFSK IN pin ( b a ck p a n e l) a re also a p p lied to IC 4 .
10
CIRCUIT D ESCRIPTION
044
IC4
2SC2 459
JJPC I 158HZ
MIC AMP
PROC
QI0,11
04 6
3SK122x2
3SK73
Q I
02, 3 04,5
2SC2075 2SC2509x2 2SC2879x 2
Fig . 6 Tra nsm itter c ircuit configu ration
IC5
AN6 12
DBM
013,14
3SK122x 2
A.T
IC4 f u n ctio n s as a S P E ECH processor. O u t p u t from IC4 is
distributed to the MIC G A IN co nt rol (front p a n e l) a n d F M cir­
c uit (RF u nit) . In S S B mode, the sig n al a p plied to the M IC
G A I N co ntrol is sent back to the IF u nit (con nector ( 2 3) MV2),
amplified by Q44 ( 2SC 2 4 59), a n d s u p plied to the b a l a n ced
mod u l ator IC 5 (A N6 1 2) . In F M or CW mode, Q44 does not
ope rate because a cut-off voltage is s u p plied to its emitte r
v i a diodes 0 8 2 a n d 046 . The sig n a l converted to 4 5 5 kHz
8.83MHz
016
2SC2538
1
RX