23
TK-290
CIRCUIT DESCRIPTION
9. Compander
C
ircuit
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.
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).
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.
Fig. 17
Compressor
Transmission path
Expander
Noise
40dB S/N
0
–20
–40
–60
–80
–100
(dB)
0
–20
–40
–60
–80
–100
60dB S/N
Output
Input
Modulator
and
Transmitter
Compressor
Input
Demodulator
and
Receiver
Expander
Output
Signal
R665
DATI
TCNT
AUDIH
MUTE
MAND
BUSY
DATO
STONE
E
SCALL
KEY
EMERG
PTT
CODE4
CODE2
TXOUT
NC
PTTIO
RXAEN
TXIN
CODE3
CODE1
RXOUT
E
CLR/
C (AUX)
RXIN
+V
A+
AUX
R414
X57-540X-XX
Component side
Fig. 18
