Motorola APX 7500, Detailed Service Manual

Page: 40 / 164

September 9, 2011 68009482001
2-12 Theory of Operation: System Communications Overview
Local paddle microphone audio is digitized in the O5 control head and sent on the CAN_AUDIO bus
from the control head to the Consolette controller card (PPLN1689). On the Consolette controller
card, this digitized CAN audio is converted to SSI audio by the Nautilus FPGA (U900) and routed to
the DSP where its gain can be adjusted via the “Controlhead Mic (TX) Gain Setting” in the
Consolette Configuration. This gain can be adjusted from -5 dB to +5 dB in 0.5 dB steps to achieve
the desired transmit deviation. Since local microphone audio is not being input to the DSP through
the Codec, whenever there are simultaneous PTTs among the priority rear panel transmit path and
the local microphone, the transmit audio on these active paths will be summed in the DSP. The only
case where this is not true is when the local microphone PTTs first and then a tone remote control
(TRC) attempts to PTT on a different channel. In this case, the Consolette will dekey and a bad tone
will sound at the local speaker. From the DSP, the Nautilus FPGA converts the SSI audio to CAN
audio which is sent over the CAN_AUDIO bus to the APX transceiver to be transmitted.
NOTE: The audio inputs to the APX Consolette are always in analog audio format. The APX
Consolette then converts them for over-the-air transmit per the selected signaling type which
can be enabled in its codeplug: Analog Conventional, Type II Trunking, APCO Conventional,
and APCO P25 Trunking (including F2).
2.3.16.1 Headset Transmit Audio
Headset microphone audio can originate from both headset connectors. This audio is input on the
high speed connector board's RJ45 Headset 1 Connector at HD (J11 pin 5) and RJ45
Headset 2 Connector at HD (J12 pin 5). Since these are single-ended microphone audio
inputs, HDST1_MIC- (J11 pin 4) and HDST2_MIC- (J12 pin 4) are both tied to ground. Each headset
path has its own PTT source associated with it, HDST1_PTT* (J11 pin 6) and HDST2_PTT* (J12 pin
6). These PTT signals are passed through octal buffer U1809 before reaching OMAP inputs
HDST1_PTT_OMAP* (U400 pin R11) and HDST2_PTT_OMAP* (U400 pin Y1). After being routed
from the high speed board to the controller card, the headsets’ microphone audio is biased and
summed through quad op amp package U1801 pin 2 with an attenuation of 6 dB. Each headset
microphone audio path has an impedance of 50 with a bias of 4.8V for the headset microphones’
internal circuitry. This summed audio from U1801 pin 1 is then input at Codec MICIN; furthermore,
the gain of this audio is adjustable via the “Headset Mic (TX) Gain Setting” in the Consolette
Configuration.
NOTE: Only APX Consolettes with the local control option consisting of an O5 control head and front
panel speaker will support headsets.