Transmit Signalling Circuits; Sub-Audible Data (Pl/Dpl) - Motorola GTX/LCS 2000 Service Manual

Transmit Signalling
Circuits
MICRO
CONTROLLER
U0101

Sub-audible Data (PL/DPL)

7-16 Theory of Operation
routed to two attenuators, which are tuned in the factory or the field to set the
proper amount of FM deviation. The TX audio emerges from the ASFIC at
U0201-H8 MOD IN, and is routed to the RF section.
See Figure 7-4 for reference for the following sections. From a hardware point of
view, there are three types of signalling:
• Sub-audible data (PL / DPL / Connect Tone) that gets summed with transmit
voice or signalling,
• DTMF data for telephone communication in trunked and conventional
systems, and
• Audible signalling including Select 5, MPT-1327, MDC, High speed
Trunking.
Note:
HIGH SPEED
G1
5
CLOCK IN
DTMF
7 G2
CLOCK
ASFIC U0201
LOW SPEED
6
C3
CLOCK
Figure 7-4 Transmit Signalling Paths
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 103 Hz, the frequency of the square wave would be 1236 Hz.
The hardware supports all three types while the radio soft-
ware determines which signalling type is available.
HS
SUMMER
5-3-2 STATE
ENCODER
SPLATTER
FILTER
DTMF
ENCODER
LS
PL
SUMMER
ENCODER
ATTENUATOR
H8
MOD IN
TO RF SECTION
(SYNTHESIZER)