Motorola pro7100 Manuel de service télécharger pdf (Page 24)

2-10 Theory of Operation

Multi switch U0251 controlled by ASFIC CMP port GCB4 selects either the external microphone

input signal or the voice storage playback signal for entering the ASFIC CMP at pin 48. The audio

signal at U0221-48 (TP0222) is approximately 14mVrms for 1.5kHz or 3kHz of deviation with

12.5kHz or 25kHz channel spacing.

The FLAT TX AUDIO signal from accessory connector J0501-5 is fed to the ASFIC CMP (U0221, pin

42) through C0541 and line FLAT TX RTN.

The ASFIC has an internal AGC that controls the gain in the microphone audio path. The AGC can

be disabled/enabled by the µP. Another feature that can be enabled/disabled in the ASFIC is the

VOX. This circuit, along with the capacitor at U0221, pin 7, provides a dc voltage allows the µP to

detect microphone audio. The ASFIC can also be programmed to route the microphone audio to a

speaker for public address operation.

2.3.3.1 PTT Sensing and TX Audio Processing

The microphone PTT signal coming from the control head is sent via the SBEP bus to the µP. An

external PTT can be generated by grounding pin 3 on the accessory connector if this input is

programmed for PTT by the CPS. When microphone PTT is sensed, the µP always configures the

ASFIC CMP for the "internal" microphone audio path, and external PTT results in the external

microphone audio path being selected.

Inside the ASFIC CMP, the microphone audio is filtered to eliminate frequency components outside

the 300-3000Hz voice band, and pre-emphasized if pre-emphasis is enabled. The signal is then

limited to prevent the transmitter from over deviating. The limited microphone audio is then routed

through a summer, which is used to add in signalling data, and then to a splatter filter to eliminate

high frequency spectral components that could be generated by the limiter. The audio is then routed

to an attenuator, which is tuned in the factory or the field to set the proper amount of FM deviation.

The TX audio emerges from the ASFIC CMP at U0221-40 MOD IN, at which point it is routed to the

RF section.

2.3.3.2 TX Secure Audio (optional)

The audio follows the normal transmit audio processing until it emerges from the ASFIC CMP TX

SND pin (U0221-44), which is fed to the Secure board residing at option connector J0551-33. The

Secure board contains circuits to amplify, encrypt, and filter the audio. The encrypted signal is then

fed back from J0551-32 to the ASFIC CMP TX RTN input (U0221-36). The signal level at this pin

should be about 65mVrms. The signal is then routed through the TX path in the ASFIC CMP and

emerges at MOD IN pin 40.

2.3.3.3 Option Board Transmit Audio

The audio follows the normal transmit audio processing until it emerges from the ASFIC CMP TX

SND pin (U0221-44), which is fed to the option board residing at option connector J0551-33. The

option board contains circuits to process the audio. The processed signal is then fed back from

J0551-32 to the ASFIC CMP TX RTN input (U0221-36). The signal level at this pin is approximately

65mVrms. The signal is then routed through the TX path in the ASFIC CMP and out at MOD IN, pin

40.

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Motorola pro7100 Manuel de service Page 24