Kenwood TK-290 Service Manual page 24

9. Compander Circuit
The term compander is a compound of compressor and
expander. The compander reduces noise by utilizing a com-
pressor and an expander.
As shown in Fig. 17, the signal input to the compressor is
compressed so that the logarithmic ratio is 1/2 with refer-
ence to –10dBV, and then output onto the transmission
path. The signal is expanded by the expander so that the
logarithmic ratio is 2 with reference to –10dBV. This re-
duces noise on the transmission path and prevents deterio-
ration of the signal quality due to noise during transmission.
Input
Input
10. Option Board Terminal
Terminals for mounting the option board are provided at
the bottom of the TX-RX unit. The table below shows the
correspondence between the board and terminals. Discon-
nect R414 and R665 in TX-RX unit when the scrambler board
is attached.
Connect the option board to the connection terminals of
the TX-RX unit.
CIRCUIT DESCRIPTION
(dB)
Compressor Transmission path
0
Signal
–20
–40
Noise
–60
–80
–100
Modulator
Compressor and
Transmitter
The TK-290 contains IC607 (TC35453F) to perform this
operation.
Pin 16 : Compressor input pin
Pin 18 : Compressor output pin
Pin 43 : Expander input pin
Pin 41 : Expander output pin
The TK-290 compander can be turned on or off only when
modulation is set to Narrow by FPU setting. The compander
cannot be turned on when modulation is set to Wide (OFF).
Expander
0
–20
–40
40dB S/N
–60
–80
–100
Demodulator
and Expander Output
Receiver
Fig. 17
DATI CODE4
CODE3
DATO
CODE2
TCNT
CODE1
STONE
AUDIH TXOUT
RXOUT
E
MUTE NC
SCALL
AUX PTTIO
CLR/
KEY
C (AUX)
MAND RXAEN
RXIN
EMERG
BUSY TXIN
+V
PTT
A+
TK-290
Output
60dB S/N
X57-540X-XX
Component side
R414
E
Fig. 18
23