Apco And Crosspatch Transmit Audio; Wireline Transmit Audio - Motorola APX 7500 Detailed Service Manual

Theory of Operation: System Communications Overview

2.3.16.2 APCO and Crosspatch Transmit Audio

The crosspatch and APCO transmit audio paths share the same Codec INP1; however, these paths
are not summed. They are mutually exclusive, so only one of these paths is routed to Codec INP1 at
any given time. The single-ended crosspatch transmit audio is input on the high speed connector
board's RJ45 Crosspatch Connector at CP_AUX_TX (J24 pin 8) and its associated PTT source
(CP_PTT*) is located on J24 pin 7. The single-ended APCO transmit audio is input on the low speed
connector board's DB25 Accessories Connector at AUX_TX (J104 pin 17) and its associated PTT
source (PTT*) is located on J104 pin 10. The PTT signals for both interfaces are passed through
octal buffer U1809 before reaching OMAP inputs CP_PTT_OMAP* (U400 pin L18) and PTT_OMAP*
(U400 pin V8). The crosspatch PTT and APCO PTT cannot be active simultaneously (only one PTT
source is active at a time), but both can be deactivated. These parameters are set in the
"Crosspatch-Hardware PTT Selection" audio parameter of the Consolette Configuration. Both the
crosspatch and APCO transmit audio paths have an impedance of 600Ÿ and are attenuated 6 dB via
quad op package U1801 (U1801 pin 6 for the crosspatch path and U1801 pin 9 for the APCO path)
before being input into analog switch U1800. Based on the "Crosspatch-Hardware PTT Selection"
setting, OMAP output CP_DISABLE (U400 pin M14) will select the appropriate U1800 input path to
be switched into Codec INP1. The gain of this audio is adjustable via the "Crosspatch In (TX) Gain
Setting" in the Consolette Configuration.

2.3.16.3 Wireline Transmit Audio

Wireline audio to be transmitted over the air is applied to the wireline interface network. This
differential audio can be input in either of two locations depending on the "Wireline Configuration"
setting in the Consolette Configuration Remote Interface Parameters page. Based on this setting,
OMAP output NUM_WIRES (U400 pin W15) will select the appropriate wireline path (two-wire or
four-wire) to be switched in via U1805. For two-wire operation, the differential audio is input on the
high speed connector board's RJ45 Wireline Connector at LINE1+ (J21 pin 3) and LINE1- (J21 pin
6). For four-wire operation, the differential audio is input on the RJ45 Wireline Connector at LINE2+
(J21 pin 4) and LINE2- (J21 pin 5). The wireline interface network consists of line matching
transformers T1801 (two-wire operation) and T1800 (four-wire operation), quad op amp package
U1806, and other discrete components. The purpose of this circuitry is to match the impedance of
the controller card to that of the wireline (T1801, T1800, K1801, K1802), block any DC components
between the controller card and the wireline (C1862, C1863, C1860, C1861), and provide protection
from surges on the line (surge arresters F1 and F2 on the high speed connector board). Solid state
relays K1801 and K1802 set the impedance for the wireline. Based on the "Wireline Configuration"
setting in the Consolette Configuration, OMAP output WL_IMPEDANCE (U400 pin P11) will select
the appropriate wireline impedance (600Ÿ or High Impedance) to be switched in via K1801 and
K1802. After passing through switch U1805, wireline transmit audio is attenuated 14 dB via quad op
amp package U1801 (output pin 14) before entering Codec INP2. At this point, the transmit audio
gain is either adjusted by the AGC (automatic gain compensation) algorithm in the DSP or linearly
via the Codec and DSP. AGC is only used when the wireline interface is being used with tone remote
control. Therefore, in order for the gain to be adjusted using AGC, "TRC" must be selected as the
"Wireline Function" audio parameter in the Consolette Configuration and then "TRC AGC
Configuration" must be enabled in the Consolette Configuration Remote Interface Parameters page.
The AGC function, when enabled, sets the wireline transmit gain based on the level of the high level
guard tone (HLGT) received. In addition, the "AGC Offset Adjustment" in the Consolette
Configuration can be used to adjust the ratio applied between HLGT and audio to compensate for
variation from the normal ratio. This may be required if there are nonlinearity in the wireline, if the
console has a non-standard level for HLGT, or if the console lacks a microphone gain adjustment or
68009482001
2-13
September 9, 2011