Trc Audio Processing - Motorola APX 7500 Detailed Service Manual

4-10
NOTE: It is not possible to select the transmit Encryption Key (CKR) through the TRC interface. Refer
to the APX 7500 CPS for more details on configuring the radio's secure settings. Encryption
Key strapping is recommended for TRC operation.
4.12.2.3.3 PTT
To make a voice transmission, first select the desired channel using the Select Frequency feature.
Then the console user also ensures that the correct secure mode (if configured) is chosen.
NOTE: For encrypted voice calls, the Console sends the request for secure mode to the Consolette
so the Consolette can encrypt the audio. The Console does not encrypt the audio associated
with coded mode calls.
Once all of the selections are made the console user invokes a PTT to start their transmission. The
requested transmission is then performed by the Consolette which routes audio from the wireline TX
interface to the radio for transmit. The transmission goes out on the currently selected air interface
(and talk group if one is chosen) using the unit ID of the Consolette's radio (not the Console's unit
ID). Once the LLGT is no longer detected by the Consolette or if the Console operator dekeys, the
Consolette will dekey. AGC can be enabled on this interface. If the mobile configuration does not
allow the PTT (RX Only Channel for example) or if any of the Channel/Coded/Clear commands
included in the PTT sequence are disallowed, the Consolette will generate a "bonk" tone and not Key
Up.
4.12.2.3.4 Monitor
When a monitor command is received, the Consolette will send a message to the mobile radio to
cause it to enter the monitor state (ex. disables Receive PL on Conventional channels). Whenever a
subsequent PTT command ends, a message is sent to exit the monitor state. The user may "quick-
key" the Consolette (briefly key-up and de-key the Consolette) from the Console/Deskset in order to
exit the monitor state.
4.12.2.3.5 Receiving a Voice Transmission
When the Consolette receives a voice transmission, the audio is provided on the wireline RX
interface to the Console. There is no ID reporting available with the TRC interface. If ID reporting is
needed, refer to
section 4.12.3 for information regarding the ACIM interface.

4.12.2.4 TRC Audio Processing

Receiver audio from the radio is passed through a guard tone notch filter within the DSP on the
Consolette controller board (PPLN1689A). This filtered audio is then applied to a line driver circuit for
transmission on the wireline to the remote Console/Deskset. The receive notch filter prevents false
HLGT detection due to possible receiver audio components near the guard tone frequency (since
with a two-wire configuration, receiver audio output and transmit audio/tone inputs are tied together
at the wireline).
Transmit audio passes to the DSP on the Consolette controller board where gain (either linear or
AGC) is applied. If AGC is enabled, the signal is automatically adjusted to a nominal -16dBm. If AGC
is disabled, a linear gain/attenuation can be applied. This level can be selected in the Consolette
Configuration Codeplug. The guard tone (LLGT) is removed from the audio prior to it being sent to
the radio for transmit.
NOTE: On two-wire operation, receiver audio is muted when HLGT is detected, so that there will be
no interfering audio signals on the wireline when the function tones are being received.
September 9, 2011
section 4.16 for information regarding the use of an external MDC decoder or
Feature Operation: Wireline Interface
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