Los Angeles County
Sheriff’s Department
480 RADIO COMMUNICATIONS SYSTEM
N. Razum
© 1998-2003
(This is an abbreviated version of this document which does not have any confidential information listed. The "full" version of the document, for official use, may be obtained through the Department.)
System Overview:
The Sheriff’s communication system is on the UHF portion of the radio spectrum within 480-490 megahertz (MHz) range. It is commonly referred to within the Department as the “480” radio system. The Department is licensed (WII-800) for 66 UHF frequency pairs (channels).
Radio communication is the best when it is done “line of sight” and is better nearer than far away. As LA County is 4083 square miles (1741 flat and 1875 mountain), this poses problems for efficient and reliable communication. “Repeaters” are placed on high peaks, or buildings, which receive transmissions by line of sight, and then re-transmit them on a different frequency from multiple hill-tops at the same time. The Department has about 60 repeater sites, all of which are strategically located in areas to provide the best communications within the County.
The Department has set-up specific frequencies to handle certain geographic locations. To dispatch calls to West Hollywood (WHD), there are 3 receivers and 2 transmitters around that location to give the best coverage to the WHD units. Deputies in Malibu may not receive WHD calls clearly as the system was not designed to cover that area. There are “County Wide” and “Area/Regional” frequencies, that do permit clear communication within larger zones. Special Units Dispatch (SUD), uses 37 receiving and 14 transmitting sites for County-wide access.
For coverage over large areas, “Repeat” communication accesses these machines, and “Direct” or “Simplex”, uses line-of-sight. “Simplex” is radio-to-radio communication and is sometimes referred to as “Talk-around” or “car to car”.
Radio Broadcasts:
The Sheriff’s Department has a radio center that dispatches calls. It is called Sheriff’s Communication Center, or SCC, and is located near Biscaluz jail in East Los Angeles. At any given time, there are between 5-25 dispatchers working on the frequencies. All frequencies are recorded and the tapes are saved for specific intervals.
A call for service received via 911, goes to the local Sheriff’s station. The local station dispatcher types the call into the computer and then sends it to SCC in East LA. The SCC dispatcher then sends the call via radio, computer, or both to the intended unit. The computers in the cars are called Mobil Digital Terminals (MDT’s) and operate on separate UHF frequencies (470MHz).
Department issue radios, either mobile or hand held, have digital identifiers that transmit the specific radio’s identifier every time the transmit button is depressed. These automatic identifiers on the Sheriff’s system are called “G-Star AID” encoders, but are commonly called “burp” or “burst” encoders. Deputies out in the field commonly refer to it as a "turkey call". These identifiers display the unit’s number on the SCC dispatcher’s computer screen. SCC can determine authorized transmissions, even if they don’t identify themselves.
Any transmission without AID is logged as a “trouble” and are logged by a computer with the date and time, as well as the receivers that “heard” the transmission. All “troubles” are investigated. DO NOT “kerchunk” dispatch frequencies to see if your radio is working.
Department radios also have emergency triggers, called “E-Triggers” or “man-down switches” which changes the radio to the emergency frequency, and transmits the radio’s identifier five times.
Frequencies:
Of the 66 Sheriff’s channels, each channel has a specific assigned task. Each Station has a dispatch frequency. Some smaller stations share a dispatch frequency with another smaller station. There are 16 Dispatch frequencies. Each station also has a local tactical frequency (L-Tac’s) for units to talk to each other to coordinate calls. Some stations share L-Tac frequencies. There are 12 L-Tac’s. Some calls require responses from neighboring stations and coordination after dispatch is done on 4 Area tactical frequencies called A-Tac’s. Some activities require County-wide coordination and are done on three C-Tac frequencies. Many Sheriff’s stations have neighboring areas that are handled by police departments not other Sheriff’s stations. Requests for service from different agencies are called Mutual Aid requests. There are 5 Mutual Aid frequencies that cover regional areas of the County and most law enforcement agencies have them programmed in their patrol car or handheld radios.
Frequencies are assigned to stations or areas and do not change from day to day, and transmitter and receiver sites are programmed for specific areas. (i.e. Altadena units know they will always use Dispatch 1, and L-Tac 8.)
Radio Call Signs
All Sheriff stations are assigned station numbers. Firestone #1, East LA #2, etc. Radio calls evolve from these numbers and the local dispatching desk out of a station adds a zero to the station number and the letter D, for Desk. As we use the letter alphabet, it is called “David” over the air. East LA desk would be “20 David”, Crescenta Valley would be “120 David”.
Special Enforcement Bureau (SEB) desk is “240 David” over the air. Since SEB units respond to all areas of the County, it has County-wide coverage. SEB shares this frequency with Aero Bureau, Emergency Operations Bureau (EOB), Psychiatric Emergency Team (PET) and and a few others.
The Dispatch frequencies are “one-way”, meaning only SCC can only hear the field deputy talking. Other people monitoring hear a beeping alert tone to let them know the frequency is in use. SUD is a “clear” frequency, everyone can hear transmission and EVERYONE is listening. Since the “exciting stuff” happens on SUD, Department “Brass” often listen to it. The news media regularly monitor it as well.