Transmit Signalling Circuits; Sub-Audible Data (Pl/Dpl) - Motorola GM-950 Manual

Transmit Signalling Circuits

5.0 Transmit Signalling Circuits
Refer to Figure 3.2 for reference for the following sections. From a hardware point of view, there are
three types of signalling:
1. Sub-audible data (PL/DPL/Connect Tone) that gets summed with transmit voice or signalling,
2. DTMF data for telephone communication in trunked and conventional systems, and
3. Audible signalling including Select 5, MPT-1327, MDC, High speed Trunking.
NOTE: All three types are supported by the hardware while the radio software determines which
signalling type is available.
MICRO
CONTROLLER
U0101
5.1

Sub-audible Data (PL/DPL)

Sub-audible data implies signalling 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 U0201 (ASFIC) at any one time. The
process is as follows, using the SPI BUS, the µP programs the ASFIC 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 PL CLK U0201-C3 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 U0201 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 U0201-H8 (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.
5C.3-12
HIGH SPEED
G1
5
CLOCK IN
7 G2 DTMF
CLOCK
ASFIC U0201
6
C3 LOW SPEED
CLOCK
Figure 3.2 Transmit Signalling Paths
HS
SUMMER
5-3-2 STATE
ENCODER
SPLATTER
FILTER
DTMF
ENCODER
PL LS
ENCODER SUMMER
ATTENUATOR
TO RF
H8
SECTION
MOD IN
(SYNTHESIZER)
GEPD 5433
Theory of Operation