PvtSQUELCHTM CTCSS Encoder/Decoder
7
MX375
4. General Description
4.1.1 Pre- and De-emphasis
Pre- and De-emphasis (6dB/octave) filters are included on-chip in the transmit path, so that the use of this device will
produce natural sounding audio (clear or private modes) when installed in modern radio communication transceivers, with
or without existing audio processing circuitry. The recommended layout is shown in block form below.
Clear
To Transmitter
Stages
Band Pass
Filter
Band Pass
Filter
Amplifier
Pre-emphasis
De-emphasis
Pre-emphasis
Modulator
Clear
From Receiver
Stages
Band Pass
Filter
Band Pass
Filter
De-emphasis
Amplifier
Demodulator
Figure 3: Transmit and Receive Paths
4.1.2 Functions and Outputs
D0-D5
Notone RX/TX
PRIVATE
ENABLE
PTL RX TONE
RX TONE
TONE
TONE
TX
RX
PATH
TONE
DETECT DECODER OUTPUT PHASE PATH
PATH STATE
Tone
Tone
1
1
0
1
1
1
0
1
1
0
1
1
1
0
0
0
0
1
1
1
1
0
0
0
1
1
1
1
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
X
1
0
X
X
1
0
X
1
0
X
X
0
0
0
0
0
1
X
0
0
0
0
0
1
X
1
1
1
1
1
0
0
1
1
1
1
1
0
0
YES
YES
OPEN
OPEN
OPEN
BIAS
BIAS
BIAS
INV
INV
CLR
X
TX, TONE
TX, TONE REV
TX, NOTONE
INCOMPATIBLE
INCOMPATIBLE
COMPATIBLE
RX, NOTONE
TX, TONE
0°
180°
X
Notone
Tone
BIAS
BIAS
BIAS
BIAS
BIAS
YES
BIAS
X
BIAS
Tone
X
BIAS
OPEN
OPEN
OPEN
BIAS
CLR
INV
CLR
CLR
CLR
CLR
X
Tone
X
BIAS
Notone
Tone
X
BIAS
OPEN
OPEN
OPEN
BIAS
0°
180°
X
Tone
YES
BIAS
TX, TONE REV
TX, NOTONE
INCOMPATIBLE
INCOMPATIBLE
COMPATIBLE
RX, NOTONE
Notone
Tone
BIAS
BIAS
BIAS
BIAS
BIAS
BIAS
X
BIAS
Tone
X
BIAS
OPEN
OPEN
OPEN
CLR
CLR
CLR
Tone
X
BIAS
Notone
X
BIAS
Table 3: Functions and Outputs
Note:
1. Algebraic functions:
RX Path On = RX × (PTL + RX Tone Decoder)
Clear Path = Notone + Private Enable + (PTL × RX × RX Tone Decoder)
Notone (D0 - D5) = 000011
Carrier Frequency = 3333Hz During inverted Path (TX or RX)
2. The Pre- and De-emphasis circuits remain in the transmit path in both the Clear and Invert Modes.
3. Power remains applied to the CTCSS tone decoder at all times.
4. During clear operation the carrier frequency is turned off to reduce spurious emissions.
© 1997 MX•COM Inc.
www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: 910 744-5054
Doc. # 20480026.007
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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