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Installation Guide
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Appendix 2 – Special Application – Carrier Sense (CS-DBA)
Intended for use in communication systems where data-customers must share channels with one
or more voice-customer(s). Refer to Dataradio’s System Engineering for details. The Carrier
Sense feature is usually factory-set at time of order.
Normal setup for “voice” transmissions:
•
Half-duplex – Transmit and Receive is done on the same frequency as “data” transmissions.
•
Voice repeater (base) – In dispatch systems, when base-originated voice transmissions take
place, all mobiles hear the voice message. Mobiles do not talk to each other directly.
Operation:
If mobile voice-transmits, the voice repeater base often puts up sub-audible tones, called “busy
tone” as an indication that the voice channel is in-use. Data-mobiles are already listening on the
repeater frequency. For the data-base station to be able to determine that a voice channel is in-use
requires the use of a “guard-receiver” listening to the voice repeater. This component is added to
the base rack.
On Carrier Sense-enabled systems, operations are on a “first-come, first-served” basis. If the
channel is voice-busy, data communications from base and mobiles are expected to wait until on-
going voice communication completes before keying up. Similarly, voice communication from
base and mobile systems are expected to check first if channel is data-busy. If it is, then voice
must wait for the data carrier to go away. Brief periods of voice communications should be in-
visible to customer applications. Long periods of voice (or interference) will delay delivery-
confirmation responses from the radio-modem and the application may timeout and resend its
data. In multi-tower systems, the use of long voice-messaging may not be recommended.
To help data-applications coexist with voice-applications, the option of having the Carrier Sense
status reflected on the DCD lead conveys the “channel is busy with voice” information to the ap-
plication so it can be made to suspend its own timeout timers. System Engineering will arrange
for this option to be set on user equipment where applicable. If enabled, toggling of DCD
may
affect application’s DMP driver if it expects DCD to remain normally active. Therefore, software
vendors may have to write or upgrade their software so that the DMP driver expects DCD to tog-
gle often and to make use of the information that DCD is conveying.
DATARADIO is a registered trademark, Gemini, Gemini PD, and PARALLEL DECODE are trademarks
of Dataradio Inc
