land mobile radio systems
TRANSCRIPT
National Communications System (NCS)ESF #2 Training Conference
LAND MOBILE RADIO SYSTEMSAND
HOW TO RESTORE THEMMajor Curtis Bowers
Plaquemines Parish Sheriff’s [email protected]
504-392-1652 June 21, 2007
Class Topics
Types of Radio Systems Simplex Trunking APCO Project 25
Frequencies Getting a system back online Radio gateway devices
Different Types of Radio Systems
Conventional Systems Simplex Operation (Radio-to-Radio) Repeater
Trunking Systems Single Site Multicast Simulcast Conventional Digital
Conventional Systems
Simplex Operation Transmissions are made over the same
frequency
Transmissions are from radio to radio – no system infrastructure needed
Conventional Systems
Carrier Squelch - open to interference
Private Line Code – keeps radio signals on same frequency from keying into radio or opening the carrier squelch
Interference audio is still present
Conventional Systems
What are the advantages of this type of system? Cost – almost any radio will work, as long as
frequency is correct Small number of users Small coverage area No infrastructure is needed
Conventional Repeater Systems
Repeaters boost transmission power for greater range
Antennas are placed on towers for increase in coverage area
5 watts 25 watts100 watts
400’
Conventional Repeater Systems
Repeater systems improve portable and mobile talk-out and talk-in coverage
A duplex system uses two frequencies. The radio transmits audio into the repeater and repeater sends out the audio at a higher wattage on a different frequency
Antenna on a tower with a repeater gives a greater range
Antenna on a tower with a pre-amp receive system increases talk-in coverage
Trunking Systems
Trunking systems consist of several repeaters controlled by computerized system
System manages users, talkgroups, and repeaters
Repeaters
Control Channel
Central Controller
Trunking Systems
Trunking systems can be a single site or consist of multiple sites over large regions
Each repeater has its own frequency and one of these repeaters is a control channel
Control channel manages information to and from the user’s radios
With this information, channels (repeaters) are assigned to users for radio traffic
Control channel is always communicating with affiliated radios
Affiliated radios send talkgroup (TG) info to system
Trunking Systems
Voice Channel Request
22 Central Controller
Control ChannelControl Channel
11
PTTPTTRequesRequestt
33
44
Trunking Systems
There can be numerous talkgroups and users on this type of system
Capacity is determined by number of channels (repeaters) the system has
There can be numerous sites (towers) used on this type of system
Size of system is limited to the number of frequencies the owner can obtain, the manufacture of the system, the version of system in service, and how much the owner can afford
Trunking Systems
Different types of multi-site systems:• Multicast: The multiple broadcast of identical audio
information on different frequencies from multiple, geographically separated sites
• Simulcast:
The simultaneous broadcast of identical audio information on the same frequency from multiple, geographically separated sites
Trunking Systems
Site 1 Site 2
Site 3
Multicast System Example
3 4 5CCVCVC
86 7CCVCVC
CCVC
21
Trunking Systems
Site 1
1 3 4 5 6VC VC
Site 2
CC VC VC
7 8
Site 3
CC VC
CC
2
8
2 5
Multicast cells Multicast cells could be could be
combinations combinations of sites in what of sites in what is also called a is also called a
Simulcast Simulcast configurationconfiguration
8
2 5
Trunking Systems
Site 1 Site 2
Site 3
3 4 5 6 7 8CCVCVCVCVCVCVCVC
21
Simulcast System Example
3 4 5 6 7 8CCVCVCVCVCVCVCVC
21
3 4 5 6 7 8CCVCVCVCVCVCVCVC
21
Trunking Systems
Simulcast “Seamless” Coverage
Site 1 Site 2
Site 3
1 2 3 4 5 6 7 8CC VC VC VC VC VC VC VC
2 3 4 5 6 7 8CC VC VC VC VC VC VC VC
2 3 4 5 6 7 8CC VC VC VC VC VC VC VC
1
1
2
2
22
2
22
2
22 2
2
Trunking Systems
Trunking systems with multiple sites have a weak link in their operation; links must go back to the master site
Links can be T-1 circuits or microwave links Multicast sites that lose their links go into site
trunking and no longer communicate with other sites
In a simulcast system, only the prime site will continue to operate; all other remote simulcast sites are off line until links are reestablished
A simulcast cell can also go into site trunking
Trunking Systems
Analog operation
Mix mode consisting of digital and analog resources
APCO 25 systems digital only
Digital is not a secure communication system, encryption is for secure communication
Analog vs. Digital
Benefits of Digital Technologies Improved Audio Quality
Digital
AnalogAudio
Quality
Signal StrengthStrong Weak
Good
Poor
Frequency Issues
License for frequencies to be restored or used
Special Temporary Authorization (STA’s) obtained
Equipment must match frequency range of system
Service equipment, software, and hardware needed to tune equipment to frequencies to be restored
Types of equipment needing tuning for frequencies: Combiners, duplexers, repeaters, tower top amp's, and radios
Restoring a Communication System
Survey what is left that still works or that can be put back in service
What type of system will be initially put in service
At tower sites you will need antennas, antenna mounts, antenna cable, cable connectors, tower climbing crew, and site master testing equipment
Restoring a Communication System
Determine how this equipment can be transported to the site
If this is a remote site how will it be connected (linked) back to other sites: microwave, phone circuits, or broadband satellite
Locate or identify a vendor or service shop that can perform many of these task for you
Restoring a Communication System
Installing a new communication system
What does the supported agency need
What type of technology will be used
What is best for the agency being supported, not what the vendors want to sell
Radio Gateways
How will this device help
Will it even work with the system or systems being connected
Get permission before connecting systems together
Set the rules for how this gateway channel or talkgroup will be used
Radio Gateways
When a problem arises with this connection, a contact person must be available 24 hrs a day
Not always the best way to connect groups of users together
Questions
Any questions welcome
Contact Information
Major Curtis Bowers
Plaquemines Parish Sheriff’s Office
8344 Hwy 23
Belle Chasse, LA 70037
504-392-1652 office
504-812-9305 cell
www.ppso.net