3. North Simulcast Site (3 tower sites/12 channels) Route 439 Spook Hill Hereford (Prime Site) South Simulcast Site (15 tower sites/24 channels) Arcadia MEMA Warren Jacksonville Red Run Fire Headquarters (Prime Site) Hickey Kingsville Highway Shop 2 Essex Allender Catonsville North Point Brady Avenue Sparrows Point Backup Prime Site for Both the North & South Simulcast system Gilroy BALTIMORE COUNTY TOWER SITE LOCATIONS
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5. TRUNKING In two-way radio communications, Trunking refers to the automatic and dynamic sharing of a small number of radio channels among a large number of radio users. A Trunking System efficiently distributes message traffic across the available channels and reduces wait time for those channels.
6. Talkgroup A Police 1 2 3 4 5 Trunking allows individual users to be combined into Talkgroups . A TALKGROUP is a group of users that have a common need to communicate with each other in order to accomplish their job. Talkgroups Talkgroup B Fire/EMS
7. The Motorola Trunked radio system uses a computer called the Zone Controller as an “operator”. The Zone Controller has 2 PRIMARY DUTIES: FIRST, to insure that only radios programmed for your specific Trunking system are used on the network. SECONDLY, to maintain and distribute the frequencies or channels on the network. Zone Controller
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10. Step 1: The following is an example of what occurs between the time you press the PTT (Push-to-Talk) button and the time you hear the Talk Permit Tones (less than ½ second). In this example, Channel 1 is the Control Channel and Channels 2 through 5 are voice channels. When you press the PTT button, the Control Channel receives the request and forwards the request to the Zone Controller that a radio is on. Talkgroup/Channel “B” wants to talk to all other users on the system selected to the same Talkgroup/Channel. Call Processing Event Sequence
11. The Zone Controller then communicates with the Control Channel at every tower and asks if they have any radios turned to Talkgroup/Channel “B” affiliated on their site. Based on the replies from the Control Channels, the Zone Controller reaches into the pool and chooses a specific frequency for the transmission. In our example, this is Channel 5. The Zone Controller then sends a message to all of the Control Channels that if they have any users selected to Talkgroup/Channel “B”, they should send those users to Channel 5. Step 2: Step 3: Step 4: Step 4 Call Processing Event Sequence (Con’t)
12. All radios monitoring the Control Channel receive this message and travel over to Channel 5. Step 5: Voice Call Processing Event Sequence (Con’t)
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15. The first tone is a “Talkgroup/Channel Busy” What is a “Talkgroup/Channel Busy”? When a radio user attempts to key up their radio and the Talkgroup/Channel where they are selected is already transmitting (i.e.“talkover” another user), they will receive a “Talkgroup/Channel Busy” prohibit tone. There are two types of “Busy” tones that you may receive on the trunking system. Trunking System Design (Con’t)
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Editor's Notes
A talkgroup is a group of users that have a common need to communicate.
Your “Sarah” is called the Zone Controller. Sarah has two primary functions. The first is to ensure that only radios programmed to work on the RISCON system are allowed to use the system and the second is to control the distribution of the frequencies kept in the pool.
The backbone of a Motorola trunked radio system begins with a series of trunked repeaters. One repeater always has the duty of transmitting and receiving the data traffic required to monitor and control the operation of the system. This repeater (channel) is called the control channel. Every tower has a designated control channel. The control channel’s primary function is to keep track of the selected talkgroup of every radio affiliated with the tower. The control channel never carries voice traffic. Therefore, if you have a 5 channel system, only 4 voice transmissions can occur simultaneously.
If you are using Push to Talk Tones, this is an example of what occurs between the time you press the PTT button and you hear the tones (about ½ second). NOTE: If you are not using PTT tones, the same process occurs during the first ½ after pressing the PTT button.
When the conversation is complete, all of the radios return to the control channel. This process can occur multiple times during the transmissions of a specific conversation. If there are times in the transmissions when no radio is keyed, the radios return to the control channel. The radio users never know the specific channel they are assigned. They just need to know that if they are selected to the same talkgroup on their radio, that they can communicate with all other radios selected to the same talkgroup that are affiliated with the system.
Trunking systems are designed based on the concept that it is highly improbable that a large percentage of users will key up at exactly the same time and that most conversations are relatively short. Your system has a “Time out Timer” set to 60 seconds. What that means is that if the radio user presses and holds the PTT button continuously for 60 seconds, at 56 seconds they will begin to hear a tone, and at 60 seconds, Sarah will take the channel away from the user. This is designed primarily for the radio that gets lodged down beside the seat with the mic keyed. This means that a frequency will not be locked out of the pool for longer than 60 seconds (demonstrate tone).
In a trunking system, only one radio can transmit at a time. If a radio is transmitting on a specific talkgroup and another radio keys up on the same talkgroup, the second user will hear a “Prohibit Tone” (demonstrate tone). The user should de-key the radio and listen. If they hear on going conversation, the user should wait for the transmission to end and then re-key the radio. If no conversation is heard, the user may be out of range on the system. Out of range will display on the radio (demonstrate tone).
System busy means that all frequencies have been assigned and “Sarah” has no frequencies remaining in the “pool” to assign. When this occurs the user receives a System Busy Tone (demonstrate tone). The user should de-key the radio. Sarah puts the radio user’s request into a queue and when a frequency is available, Talk Permit Tones (demonstrate tone) are sent to the radio. After the user receives the Talk Permit Tone, they have 3 seconds to key up the radio or Sarah will assign the frequency to the next user in the queue. NOTE: If the user re-keys the radio before receiving the PTT tones, their initial request is cancelled and they are then placed back in the queue.
Describe how radios and dispatch consoles will perform when a site is in Site Trunking.
Describe how radios and dispatch consoles will perform when a site is in Failsoft.
Describe how radios and dispatch consoles will perform when a site is in Failsoft.
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