expected for the current
programmed squelch threshold,
then the processor analyzes the
expected signaling programmed on
the current channel table.
In case of not any signaling is
required, or the signal has been
detected, the processor ask to the
audio processor (U5) to open the
audio path, unmuting the audio
amplifier (U10).
4.2.4. Virtual VOLUME CONTROL
The potentiometer position (RV1) is
measured by one analog to digital
converter on the audio processor
(U5), and then the information is
reported to the main processor. The
firmware immediately adjusts the
audio processor path gain to get the
appropriate overall circuitry volume
control.
Minimum volume, emergency and
private audio level are controlled
only by software overriding the
information received from the DAC
on U5.
4.2.5. Sub audio signaling
Received sub audio signaling like
CTCSS and DCS are received and
processed by the receiver (U1) then
detected on the audio processor
(U5). Once decoded, the sub audio
signaling is reported to the
processor where the firmware
compares it with the value
programmed into the current
channel programming.
If the received signaling matches
the channel programming, then the
main processor (U8) requests the
audio processor (U5) to open the
audio patch.
4.2.6. ANALOG AUDIBLE SIGNALING
DTMF signals, MDC1200 and tone
signals are processed and decoded
by the audio processor (U5).
Decoded information or received
tone is reported to the main
processor (U8).
4.2.7. DIGITAL AUDIO PROCESSING
Digital received information is
processed by the receiver DSP (U1)
then delivered to the audio
processor (U5), which includes a
high speed (4FSK) modem.
Data decoded by the modem is
transferred to the main processor
(U8) which de-encrypts the
information, checks the integrity,
corrects the wrong bits and extract
the audio information form the
received frame.
The portion of the data received,
error free, is moved to the vocoder
(U6).
The vocoder re-builds the audio
from the compressed data then
applies filter it, adjust the volume
RECEIVER
[U1]
