SmarTrunk Systems ST-9116C, Руководство по обслуживанию, Страница: 9 / 67

ST-9116C SM R 1.1 SMARTRUNK SYSTEMS, INC. 9
The detected audio is amplified,
filtered and conditioned inside of
U35 which also includes a de-
emphasize filtering for received
audio signals.
The output of the filtered and
conditioned audio is fed into one
ADC converter of the main
processor where it is converted to
PCM audio to be processed and
switched
as per application
requirement.
One independent analog filtered
output is fed direct to transmit
audio processor for analog repeater
mode.
4.2.3. VIRTUAL SQUELCH CIRCUIT
RSSI is measured by the receiver
(U8) as the result of the analysis of
the signal and the noise of the
carrier. The output is sent to the
main processor (U37) as a digital
frame, which is analyzed by
repeater firmware.
In other way, R123 potentiometer
position is read by one ADC input
on the RX Audio Processor (U35)
the value between -132dBm and -
30dBm is calculated in agree to the
potentiometer angle.
If the RSSI is higher than the
expected value of squelch threshold
calculated and the monitor function
is enabled working in analog mode,
then the speaker is unmuted and
the PWM incoming audio (PCM) is
delivered to the PWM filter to be
integrated then it is fed to the
amplifier.
4.2.4. VIRTUAL VOLUME CONTROL
The PCM audio can be sent to the
speaker in case of monitoring is
required. On this case, the
processor generates a PWM audio,
which is filtered then delivered to
the audio Power Amplifier (U36).
Monitor audio volume control is
based on the reading of the volume
potentiometer (R131) by one of the
ADC inputs of the RX Audio
Processor (U35) then the value is
sent to the main processor through
the SPI bus.
Main Processor (U37) adjusts the
PWM level in agree to the desired
audio level.
4.2.5. SUB AUDIO SIGNALING
Received sub audio signaling as
CTCSS and DCS are received and
processed by the receiver (U8) then
detected on the audio processor
(U35). Once decoded, the sub audio
signaling is reported to the
processor where the firmware
compares it with the programmed
into
the current channel
programming.
If the received signaling matches
the channel programming, then the
main processor (U37) requests the
audio processor (U35) to enables
the analog repeater mode
4.2.6. ANALOG AUDIBLE SIGNALING
DTMF signals, MDC1200 and tone
signals are processed and decoded