Sub-Audio Signaling Processor
FROM RX
DISCRIMINATOR
Page 9 of 24
MX805A
MX805A RX LPF
Gain = 6dB
MX805A
RX AMP
+
15
16
17
14
RX AMP IN
13
+
_
EXTERNAL
OP-AMP
NOTE 6
(see p.4)
_
C9
270k
R9
100k
D2
D1
R3
20
MX805A
COMPARATOR
+
21
COMPARATOR IN
19
_
15
m
F
COMPARATOR
OUT
V
DD
R10
R11
D.C. RESTORATION
LEVEL SHIFT AND AMPLIFY
Figure 4: MX805A Input Components using and External Op-Amp
4 General Description
4.1
Glossary
Continuous Digitally Coded Squelch
Continuous Tone Controlled Sub-Audio Squelch
Digital Private Line
Logic Trunked Radio
Non-Return-to-Zero
Filter Cutoff frequency
Sub-Audio Rx frequency
Sub-Audio Tx frequency
Tone frequency
Xtal/Clock frequency
NRZ RX baud rate
NRZ TX baud rate
Audio input signal.
DCS
CTCSS
TM
DPL
TM
LTR
NRZ
f
CO
f
CTCSS IN
f
CTCSS OUT
f
TONE
f
XTAL
R
NRZRX
R
NRZTX
s
INPUT
4.2
4.2.1
Operating Modes
NRZ Encoding
The NRZ Encoder is formed by a shift register and the TX Sub-Audio Lowpass Filter. Data loaded from the
Command Data line is output one 8-bit byte at a time from the NRZ Tx Data Register. The output data level
may be adjusted and filtered. Data may be pre-emphasized via a C-BUS command. The expected Rx baud
rate is programmed as the NRZ Tx Baud Rate (R
NRZTX
). See Table 8
4.2.2
CTCSS Encoding
The CTCSS Tone Encoder is comprised of a clock divider programmed by an 11-bit binary number (Q)
loaded to the CTCSS Tx Frequency Register (See Table 8) via the C-BUS Command Data line.
The square-wave output of the encoder is fed through the Tx Level Adjust variable gain block to the Tx
Sub-Audio lowpass filter, a variable gain bandwidth circuit controlled by 4-bits (P) if the CTCSS Tx Frequency
Register. The Tx Sub-Audio output is a sine-wave. Standard and nonstandard sub-audio tones are available.
A CDCS turnoff tone may also be generated.
ã
2001 MX-COM, Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
All trademarks and service marks are held by their respective companies.
Doc. # 20480116.005
CMLMICRO [ CML MICROCIRCUITS ]
