Motorola MTR2000 T5544 Instruction / Field Service Manual page 188

Station Control Modules
10
Microphone
Microphone audio passes through preamp/bias generator circuitry to a switch
which selects mic or MRTI TX Audio, and routes the result to Codec #2. A sep-
arate path from the preamp output routes mic audio to the MRTI RX Audio output.
This allows mic audio to reach the MRTI output without appearing on the local
speaker. Gain in the mic audio paths is chosen to match the required MRTI levels.
Discriminator Audio
DISC RX Audio is generated by linear Codec #5. Normally it is a wideband RX
audio signal, available on the backplane for the system connector, the TCC con-
nector (as Trunk RX Data), and for any option cards. However, it has three other
functions as well:
• Under the influence of the Audio Mode input on the system connector, the
signal is changed to band-limited RX audio with optional de-emphasis and
squelch.
• In line test mode, Line 1 input audio from the Wireline Interface Board
(WIB) is routed to this output for level checking and test purposes.
Auxiliary TX Audio
The system connector input, Aux TX Audio, provides a path for audio from exter-
nal equipment to reach the transmitter without passing through the wireline. The
Audio Mode input switches it between wideband audio which is only splatter-fil-
tered, and audio which is band-limited and pre-emphasized before being splatter-
filtered. In either case, the audio reaches the DSP via codec #1. In line test mode,
this input is routed to the Line 2 output for level setting and test purposes. In ad-
dition, for special applications, the signal can be routed directly to the exciter (i.e.,
does not pass through the DSP). There is no adjustable gain required for this in-
put.
68P81096E32-E
08/06/07