Transmit Signalling Circuits; Sub-Audio Data (Pl/Dpl) - Motorola CM160 Service Information

Transmit Signalling Circuits

8.0 Transmit Signalling Circuits
MICRO
CONTROLLER
U403
From a hardware point of view, there are 3 types of signaling:
• Sub-audible data (PL / DPL / Connect Tone) that gets summed with transmit voice or
signaling,
• DTMF data for telephone communication in trunked and conventional systems, and
• Audible signaling including MDC and high-speed trunking.
Note: All three types are supported by the hardware while the radio software determines which
signaling type is available.
8.1

Sub-Audio Data (PL/DPL)

Sub-audible data implies signaling whose bandwidth is below 300Hz. PL and DPL waveforms are
used for conventional operation and connect tones for trunked voice channel operation. The
trunking connect tone is simply a PL tone at a higher deviation level than PL in a conventional
system. Although it is referred to as "sub-audible data", the actual frequency spectrum of these
waveforms may be as high as 250 Hz, which is audible to the human ear. However, the radio
receiver filters out any audio below 300Hz, so these tones are never heard in the actual system.
Only one type of sub-audible data can be generated by U504 (ASFIC CMP) at any one time. The
process is as follows, using the SPI BUS, the µP programs the ASFIC CMP to set up the proper low-
speed data deviation and select the PL or DPL filters. The µP then generates a square wave which
strobes the ASFIC PL / DPL encode input LSIO U504-pin 18 at twelve times the desired data rate.
For example, for a PL frequency of 103Hz, the frequency of the square wave would be 1236Hz.
This drives a tone generator inside U504 which generates a staircase approximation to a PL sine
wave or DPL data pattern. This internal waveform is then low-pass filtered and summed with voice
or data. The resulting summed waveform then appears on U504-pin 40 (MOD IN), where it is sent to
the RF board as previously described for transmit audio. A trunking connect tone would be
generated in the same manner as a PL tone.
44
HIGH SPEED
19
CLOCK IN
(HSIO)
82
SPI
BUS
85
80 18 LOW SPEED
CLOCK IN
(LSIO)
Figure 2-8 Transmit Signalling Path
HS
SUMMER
5-3-2 STATE
ENCODER
SPLATTER
FILTER
DTMF
ENCODER
ASFIC_CMP U504
PL
ENCODER SUMMER
ATTENUATOR
LS
40
SECTION
MOD IN
(SYNTHESIZER)
2-17
TO RF