Glossary
Here's a glossary of terms that may help you understand the 800MHz trunked radio system a little better.
800 MHz
This refers to the range of frequencies that will be utilized in the radio network. Usually this term is applied to any network that broadcasts on frequencies between 700/800 MHz.
Analog
Whenever a person speaks, sound is projected in the form of a sound wave. These waves move at a certain frequency that determines the pitch of the sound. An analog radio network transmits the actual wave of a person's voice over the air by modulating it onto a radio frequency carrier. An analog network operates differently from a digital network, which converts the vocal sound wave into a digital bit stream of ones and zeros. This information is then sent over the air, and eventually converted back into an analog wave to be heard. The Phoenix 700/800 MHz network uses a digital format that will replace an analog format.
Bonk
Sound emitted when 2 radio users are attempting to talk at the same time. A bonk means you will have to wait until the other user is finished talking before you are allowed to talk.
Conventional
A conventional radio network allocates specific frequencies to specific groups of radio users permanently. If nobody in a particular group is transmitting on their assigned frequency, then that channel remains open. This is in contrast to a trunking network which assigns frequencies to users only when they are needed, which can be more efficient. The 800 MHz network is a trunking network, and will replace a conventional network.
Coverage/Coverage Area
A radio network's coverage area refers to the entire area that gets a strong enough signal from the network for a radio in the field to transmit and receive. Once a signal from a network degrades so badly that it is essentially useless, and all transmissions are bad or impossible, then that area is considered to be out of the coverage area. The 800 MHz digital network has a coverage area that spans the entire Phoenix metropolitan area. The coverage area is often called the "footprint" of a network.
Digital
The term "digital" refers to the method of expressing information in one of two different electronic states, which are usually designated as ones or zeros. These ones and zeros form a pattern that can be translated into all kinds of information. Relaying digital information through an electrical system is done by transmitting electronic pulses with one of two distinct electrical charges.
Frequency
All radio networks broadcast their transmissions through antennas on a certain frequency. The number of the frequency refers to the number of times that an electromagnetic wave repeats in the span of one second. For example, a transmission being sent at 800 MHz means that its wavelength repeats 800,000,000 times per second. With sophisticated electronic equipment, these waves can be engineered to carry large amounts of information over great distances.
Intelligent Site Repeater
An Intelligent Site Repeater is a radio site which utilizes a device called a site controller. This controller can perform all call processing and channel assignment tasks that are required to operate the site's base stations. Intelligent Site Repeaters will be utilized in the 800 MHz digital radio network.
Interoperability
This term refers to the capability of separate and independent entities to work together seamlessly. The 800 MHz network will promote full interoperability between all participating agencies.
PTT (Push to Talk)
This term refers to the button on a radio that a user pushes to transmit. When somebody wants to talk over the air, they depress the PTT on their portable radio, mobile radio, or dispatch console, and if there is an available frequency, they will be able to speak over the network. When a user presses the PTT, that is often referred to as "keying" the radio.
Repeater
A repeater is a piece of equipment that acts as a transmitter and a receiver. In a radio communications system, repeaters are used to extend the coverage of a wireless transmission. The repeater accomplishes this by first receiving a signal that has been transmitted from some other location, then amplifying and re-transmitting that signal from an antenna, thus giving the original transmission a boost.
Simulcast
A radio network that is simulcast transmits information from each of its transmission sites simultaneously. This means that when a radio user transmits from his/her radio, that transmission is rebroadcast from every tower or antenna that is part of the simulcast system. Because of this technique, any radio can pick up any transmission, regardless of its location. The 800 MHz network has several simulcast networks working within the whole system.
Site
Also called transmit site, cell site, radio site, or antenna site. Any radio network transmits and receives its signals through antennas that are placed strategically in different locations throughout their desired coverage area. These places are called sites. Usually the antennas at these sites are mounted high above ground on towers or on the sides of buildings. The 800 MHz network utilizes approximately 20 radio sites, including sites on North Mountain and South Mountain.
Talk-Permit-tone
Tone that signals you to begin talking. Once the PTT is depressed, two quick beeps can be heard. You know have an assigned frequency and the ability to transmit your message.
Talkgroup/Radio Channel
A talkgroup is a group of radio users that are linked to each other through the radio system. For instance, if any member of a talkgroup initiates a call, any member of that group will hear that transmission.
Trunking
This term refers to a type of communications system that draws from a pool of available frequencies, and assigns them only when they are needed. For example, in the 800 MHz trunked network, when a radio user wishes to talk over the air, they push their transmit button and the system dedicates a frequency to broadcast that user's transmission. After the user lets go of the transmit button, the system can reassign that same frequency to a completely different radio. Trunking is different from a conventional radio network, which assigns one dedicated frequency to a group of radios indefinitely. In a conventional system, if nobody in a particular group is transmitting, their assigned frequency sits unused and is essentially wasted. Trunking can be more efficient, since any available frequency can be used whenever it is needed.
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