ENP Study GroupPrinciples of Telecommunications-RadioBROUGHT TO YOU BY: THE FLORIDA NENA EDUCATION COMMITTEE

Radio Spectrum-3kHz- 300GHz

LicensingRadio Wave

Wavelength

Band

Channels

Trunking

Conventional

Repeater

Simplex

Simulcast

Voting

Digital signal

Analog signal

Data

GPS & DGPS

FCC- Federal Communications Commission

Radio Waves Electromagnetic waves that travel through the atmosphere.

To better understand properties of Radio Waves, consider waves in the ocean.Similar to radio waves, they are a series of peaks and valleys.

Images and descriptions courtesy of: Understanding Wireless Communications in Public Safety- A guidebook to Technology, Issues, Planning and Management. Published by the National Law Enforcement and Technology Center. http://transition.fcc.gov/pshs/docs-best/imel-wireless03.pdf

Wavelength & Frequency The length of a wave is measured from one point on a wave to the next similar point.

◦ i.e. from peak to peak, or valley to valley

◦ A wave with a short wavelength would have peaks that are relatively close to each other.◦ A wave with a long wavelength would have peaks that are further apart.

Properties of Radio Waves In a public safety radio system carrying, a person’s voice is converted to electrical energy that rides a wave.

The size or length of the wave is dependent on the frequency used by the radio system.

The distance that a wave can travel is dependent on factors such as the frequency, wavelength, humidity, obstacles interference, etc.

Waves are similar to a long distance runner. The further the runner goes, the less energy he has.

Public Safety BAND plans VHF-low (Very High Frequency)

◦ 39-72 MHz ◦ Travel greater distances, often used for intercity or statewide

communications.◦ Prone to problems with atmospheric skip.

VHF-high◦ 145-159 MHz

◦ Used by Police, Fire and EMS for day-to-day communications.

UHF (Ultra High Frequency)◦ 400, 500, 700, 800, 900 MHz

◦ Used by Police, Fire and EMS for day-to-day communications.

Channels The FCC groups frequencies within a BAND into individual CHANNELS which are licensed to public safety radio systems.

Simplex radio systems As might be inferred by the name, SIMPLEX radio systems are the simplest of systems.

SIMPLEX radio systems utilize portable, mobile and possibly base station radios that ALL transmit and receive transmissions on the SAME channel.

◦ Think: walkie-talkie, CB, FRS (Family Radio Service) or GMRS (General Mobile Radios Service) radios

SIMPLEX is used when units do not need to communicate over great distances.◦ E.g. Firefighter in a building talking to the Incident Commander or truck pump operator.

All modern public safety radios have the ability to operate in a SIMPLEX mode.◦ This is usually referred to as ‘direct’ or ‘talk-around’.

Repeater based radio systems If communications is needed over a greater distance (larger coverage area), a system of repeaters is used.

A repeater system requires two channels. One for “talk-in”, the other to retransmit.

Simplex vs. Repeater

Frequency A“talk-in”

Frequency B repeat

Receive antenna 60’+ above ground

Transmit antenna at greater height

Power limitations Portable radios in the public safety bands generally transmit 3-5 Watts

Mobile radios in the public safety bands generally transmit 35-50 Watts

Base stations and repeaters generally transmit 5-100 Watts

To increase spectrum efficiency and quality, the FCC imposes power restrictions on radio systems.

◦ In the past a jurisdiction would put an antenna in a central location, with an antenna as high as possible, with a large amount of power to push the signal as far as possible.

◦ Radio systems are now engineered so that frequencies may be re-used by other jurisdictions. (e.g. 75 miles between systems).

Power systems (battery packs) and antenna’s must be considered as well.

Trunking (Trunked Radio Systems)

Consider a repeater based radio system for a county that utilized the following in their system:◦ EMS 1 radio channel◦ FIRE 3 radio channels (dispatch, tactical, command)◦ Law Enf. 3 radio channels (PD, SO, car-to-car)◦ City Gov’t. 1 radio channel◦ County Gov’t. 1 radio channel

This small county maintains a total of eight radio channels.

The county EMS normally runs two ambulances. One radio channel is more than sufficient. Now, imagine a large Mass Casualty Incident (MCI) requiring EMS coordination with surrounding EMS providers, hospitals and trauma centers.

How TRUNKING worksCONVENTIONAL RADIO SYSTEM TRUNKED RADIO SYSTEM

Voting Receivers Since Portable and Mobile radios have significantly less power than do repeaters, there are often areas where users may be able to hear radio traffic, but are not be able to get a transmission into the system.

Satellite (remotely located) receivers may be located strategically throughout the required coverage area.

These receivers receive the signal from the portable and mobile radios and send the signal, over the microwave or landline to the central controller, which ‘votes’ (or selects) the best audio signal. This signal is passed to the system and that is what the other users hear.

Simulcast A simulcast system transmits radio traffic across multiple synchronized transmitters (sites).

Simulcast systems are often engineered with voted receiver sites allowing for robust and wide spread coverage systems.

Digital vs. Analog Newer radio systems (including P25) use digital signaling to send the voice through system. A device in the radio called a voice encoder or ‘vocoder’ transmits the analog signal into a digital signal which is transmitted through the system and then converted back to an audible signal.

Traditional radio systems carried analog signals through the system. An analog system uses the voice’s vibration.

Data Data transmissions may also be sent across a radio system.

Simple data transmissions may be the radio call sign transmitted at regular intervals, or to control remote equipment.

Many systems utilize a special signal to indicate an emergency.

Mobile Data systems may use radio systems for data transport.

GPS location information can also be sent across a radio system.

Some systems have been used to transport live video feeds.

GPS The Global Positioning Service was developed by the DOD as a worldwide navigation and positioning tool.

GPS relies on (24) satellites orbiting the earth to serve as reference points using time measurements from at least four satellites. These can be translated into lat/long, altitude, course and speed.

Differential Global Positioning System (DGPS) relies on a calculation from a second receiver at a fixed location to determine the error in the signal.

Questions