M805-00
Quasi-Synchronous Operation With ADNs
5.3
Copyright TEL
30/04/95
5.1
Operation With Audio
Distribution Network Type 1
Figure 5.1 Block Diagram Of Audio Distribution Network Type 1
The Audio Distribution Configuration 1 (ADC-1) system is one of the networks cur-
rently available that is designed to operate with a Quasi-Synchronous system. Figure 5.1
shows how the T805 Quasi-Synchronous system is integrated into the ADC-1 system.
Speech (HF) audio from the ADC-1 system is passed into the TSGM where, under nor-
mal operation, an internal switching arrangement passes it to the appropriate output
port. This output is then passed into the facility port of the ADC-1 digital switch con-
troller where it is digitised and passed on to all the RICs (PCM digital to analogue den-
coder cards) in the Quasi-Synchronous system. The RICs then convert the PCM code
back to an analogue signal. The audio output of the RIC is then passed into its corre-
sponding LEM.
Because of limitations in PCM technology, the RIC's frequency response is limited to the
300Hz to 3kHz band and so CTCSS (or training signals below 300Hz) cannot be passed
to the LEMs via this path. The CTCSS is either generated in the TSGM itself or fed into
it from an external source. The TSGM's LF output is fed directly into all the LEMs in the
Quasi-Synchronous system via an analogue path where it is internally summed with the
HF audio and processed/equalised. The combined speech/CTCSS output is then fed
directly into the LEMs' AIM.
If there is a requirement to remove a site from the Quasi-Synchronous system (breakout
mode) and have it operate independently, a logic output (labelled ICCS) from the RIC
PCM Network
controller
PCM dencoder
card #1 (RIC #1)
PCM dencoder
card #2 (RIC #2)
PCM dencoder
card #n (RIC #n)
PCM highway
ICCS
(breakout
control)
ICCS
(breakout
control)
ICCS
(breakout
control)
LEM #n
LEM #2
3
4
3
4
3
4
Monitor
receiver audio
To AIM
To AIM
To AIM
2
2
2
1
1
1
LEM #1
TSGM
LF
audio
HF
audio
2
1
2
External CTCSS
(optional)
Speech
1
Содержание T805
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