118 lines
5.3 KiB
Plaintext
118 lines
5.3 KiB
Plaintext
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MOTOROLA TRUNKING SYSTEM
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This file is an over view of the Motorola Trunking system.
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The concept:
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Trunking is a means of having a large amount of Two way radio users on a
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few channels without the bother of waiting for the other users to clear a
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channel or as in conventional repeaters having all other users on that
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channel able to monitor your voice traffic.
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Interconnect to the telephone lines available as an option.This allows
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phone calls to be made and recieved as well as dispatch.
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The Equipment:
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Trunked systems in the U.S. currerently are all in the 800 MHZ range with
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the systems being repeater type systems. The main differences is where to put
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the logic and control package and what type of signalling system used.
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The MOTOROLA system was designed with the logic in a central control unit
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located at the base repeaters and a primarily digital format for signalling
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between mobiles and the system. Data at 3600 baud is primarily used, also
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used is 150 baud and 3 tones (1800 hz,105 hz,and 163 hz).
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Terms used:
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For our uses we will suppose that the user is a rapid package delivery
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service with roving supervisiors,roving expiditers,standard delivery people
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and you the Boss.
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FLEET: The entire group of mobile units and portables.
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SUBFLEET: A user defined section of mobiles,portables, and or base units. A
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subfleet can be just the delivery people and a base;or the Boss and his
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supervisiors or any other combination needed. The mobile units can be fixed
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to one subfleet or be able to move between subfleets.(numd´r of subfleets
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acsessable by a single mobile can be restricted). Up to 15 subfleets per
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fleet and numbers of fleets are limited only by the number of channels in
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a system; to a max of 20 channels with 305 fleets.
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We will now run through a call on a basic system. The system is 5 channels
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with one channel dedicated to data. Data channel is 3600 baud only.
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When the mobile is turned on it scans for the continuously transmitted
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background data stream. This stream also contains the system Id. The mobile
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if assigned to this system will decode the Id and sit on this channel. If a
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conversation for this mobile is in progress then the mobile decodes the data
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and joins the in progress conversation.
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When the mic button is depressed the mobile sends on the data channel a
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request for service(known as the inbound signaling word ,ISW.). The ISW
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contains the following information: Fleet,Subfleet, and Unit ID.
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The system hears the request and checks all channels for an activity. When
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it finds one it sends back on the data channel the following:
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FLEET,SUBFLEET,UNIT ID,AND CHANNEL INFORMATION. This is known as an Outbound
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signalling word,OSW.
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The OSW will send the mobile to a channel by programming its synthesiser.If
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all channels are busy the OSW will cause a busy tone to be heard and a busy
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lamp to light. The request will be held and the system will call back when
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a channel is available.
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With the requesting mobile now on the voice channel the system still sends
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the OSW on the data channel and sends a 3600 baud handshake on the voice
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channel. The handshake has Fleet, Subfleet and Unit Id in it.
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When the requesting mobile decodes the handshake it responds on the voice
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channel with 80 msec of 1800 hz tone.This tells the system that it is on the
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voice channel.
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The system responds by changing the handshake from 3600 to 150 baud data
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using less devation. The 150 baud has in it Fleet and Subfleet data. The
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system now sends all other mobiles that are in the same fleet and subfleet
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to that voice channel. When they arrive they decode the fleet and subfleet
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data and unmute the speaker to recieve the voice message. OSW still being
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sent on data channel
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The requesting mobile now switches to sending the subaudable connect tone
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(105 hz) while voice is being transmitted.
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The system hears the connect tone and holds the channel for that subfleet.
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When the requesting mobile unkeys for the first time it sends a 200 msec of
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disconnect tone(164 hz). It also hears the 150 baud data and unmutes the
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speaker.
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The disconnect tone starts a time out timer in the system.
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All mobiles now on the voice channel may use the channel. Each time any
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mobile keys up it sends only connect tone. This tone tells the system that
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the channel is in use and resets the time out timer.
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When the conversations are done the timeout timer will expire in the system
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causing a disconnect data word to be sent on the voice channel.This mutes the
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speakers of all the units on that voice channel and all units return to the
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data channel. The OSW on the data channel is dropped.
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The system will put that fleet id in the recent user queue.It will have first
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call on the system instead of a new request by a different subfleet. This is
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to ensure no waiting of a channel in the middle of a voice message if someone
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lets the system drop out.
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This system has a lot of nifty other features including what I call the Boss
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call and the call from on high. As this is long enough already,I will save
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them for another time.
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If you have any questions leave a msg in the forum in section 3 and I will
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be glad to give you any information I can.
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JOE BARTLETT 70675,306 ALT.SYS.COMS.
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