Motorola pro7100 Manuel de service télécharger pdf (Page 25)

Theory of Operation 2-11

2.3.4 Transmit Signalling Circuits

Refer to Figure 2-4 for the descriptions that follow.

Figure 2-4. Transmit Signalling Paths

The three types of transmit signalling paths are as follows:

• Sub-audible data (PL/DPL/connect tone) summed with transmit voice or signalling

• DTMF data for telephone communication between trunked and conventional systems

• Audible signalling

2.3.4.1 Sub-Audible Data (PL/DPL)

Sub-audible data implies signalling whose frequency/data rate 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 U0221 (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 U0221-18 at twelve times the desired data rate. For

example, for a PL frequency of 103Hz, the frequency of the square wave is 1236Hz.

This drives a tone generator inside U0221 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 U0221-40 (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.

NOTE

All three types are supported by the hardware while the radio software determines which

signalling type is available.

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Motorola pro7100 Manuel de service Page 25