Subject: [NEXTEL-1] Lesson One: Two Way Radio

From: Marcel <[email-masked]>
Date: Tue, 08 Apr 2003 20:45:45 -0400

Lesson One: Two Way Radio .

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IT Course

Module Three

Section Six: Wireless Communications

Introduction to Lesson One

The first commercial two-way radio was used in the early 1930s.
Today it is hard to imagine how businesses and institutions, such
as hospitals and fire stations, would function without it. This lesson explains several types of two-way radios and how they operate.

In this lesson you will learn:

The description of two-way radio

How the two-way radio operates

Functions of the two-way radio

Index
|

Resource |

Glossary |
Outcomes |
Help

© Copyright
NB Distance Education Inc.

IT Course

Module Three

Section Six: Wireless Communications

Lesson One: Two Way Radio ..............page 1 of 5

Description of a Two Way Radio

A two-way radio system allows a two-way conversation with at least one user mobile. In
1933, the New Jersey police department became the first user of a two-way radio system.
Before this, radio systems were used for one way transmissions only. This did not allow
the recipient of the call to reply to the caller. During the 1940s, particularly in war
time, the need for two-way communications escalated rapidly.

One major application for two-way radio systems is in the public service. Various types of emergency vehicles use the two-way radio system, including fire, police and ambulance services. This
allows a fast response to emergency situations as they arise and enables the vehicle
attendants to have constant contact with the necessary support personnel throughout the
course of the event.

Index | Resource | Glossary | Outcomes | Help

© Copyright NB Distance Education Inc.

IT Course

Module Three

Section Six: Wireless Communications

Lesson One: Two-way Radio ..............Page 2 of 5

Description of a Two-Way Radio

Two-way radio systems offer financial benefits, particularly pertaining to businesses.
They can better service their customers and save time and fuel due to reduced travel
times.

For example, a telephone company technician could be sent to restore service to a
telephone at a fuel-oil deliverer. The trouble is quickly fixed and the company begins to
receive calls for fuel again. Just after the technician leaves, a line at a taxi company
goes out of service. Since the taxi company is just next door to the fuel-oil deliverer,
the dispatcher radios the technician who immediately visits the taxi company and repairs
the telephone. The two-way radio used by the telephone company resulted in quick service
and limited business loss for the company. Without the radio, another truck would have
been sent, or the dispatcher would have had to wait until the first technician returned to
the office.

Index | Resource | Glossary | Outcomes | Help

© Copyright NB Distance Education Inc.

IT Course

Module Three

Section Six: Wireless Communications

Lesson One: Two-way Radio ..............Page 3 of 5

How A Two-Way Radio Operates

A basic two-way radio system is made up of five basic components:

the microphone, which converts sound to an electrical signal;

the transmitter, which combines the electrical signal with a carrier frequency;

the antenna, which transmits the modulated carrier and receives a modulated
carrier signal;

the receiver, which separates the electrical voice signal from the carrier
frequency;

the speaker, which converts the recovered electrical signal to sound.

Index | Resource | Glossary | Outcomes | Help

© Copyright NB Distance Education Inc.

IT Course

Module Three

Section Six: Wireless Communications

Lesson One: Two-way Radio
..............Page 4 of 5

How A Two-Way Radio Operates:

There are 6 basic steps in the operation of a two-way radio:

The first step involves pressing the transmit button and speaking into the microphone. The microphone converts the voice into an electrical signal much like the transmitter on a telephone.

The electrical signal generated by your voice is a low-frequency signal. As we saw in the section on basic speech, the majority of our speech is in the 100 Hertz to 9,000 Hertz range.
This frequency range cannot be transmitted over the airwaves very far, so
the transmitter modulates a high frequency carrier (Radio Frequency) with the voice signal.
The type of modulation used is called (Frequency Modulation) or FM. The term FM should be familiar to you from your stereo. You have a choice of listening to either AM (Amplitude Modulation) or FM on your stereo and the choice is usually FM because it sounds better. FM's resistance to noise makes it the superior quality modulation, it thus dominates the two-way market. If you listen to 100.1 on the dial, it means that you are listening to music which has been modulated on a carrier frequency of 100.1 Million Hertz.

Once the voice signal has been modulated to a higher frequency, it is amplified (boosted in power) and sent to the antenna. Once sent to the antenna, the signal is transmitted into the air. The antenna can transmit the signal in all directions equally (conventional antenna) or the antenna can be designed to transmit the signal in one particular direction (gain antenna).

The receiving antenna may be another fixed antenna, an antenna located on a vehicle (mobile). The receiving antenna passes the signal on to its receiver.

The receiver begins to reverse what the transmitter sent. Like your stereo receiver, it removes or demodulates the carrier out of the original voice signal. If you are listening to 100.1 MHz on the dial, the receiver is subtracting that frequency out of the signal leaving only the original demodulated voice signal. The signal is then sent to the speaker.

The speaker converts the recovered electrical signal to sound.

Index
|

Resource |

Glossary |
Outcomes |
Help

© Copyright
NB Distance Education Inc.

IT Course

Module Three

Section Six: Wireless Communications

Lesson One: Two-way Radio
..............Page 5 of 5

There are three types of radio systems as follows:

Central Dispatch

A central radio system called the base station transmits a message which is received by one or more people tuned into the same frequency. The recipient may, in turn, respond to the message or converse with the dispatcher. An example of such a system is taxi cab dispatchers, who dispatch all the cabs with the cab drivers acknowledging their orders.

Unit-to-unit

Outfitted with mobiles or portables this system allows each person to talk and listen. Everybody with a unit is able to hear each
message. The mobile units get their power from the battery of the vehicle they are installed in or from a battery in the portable. Units consist of a transmitter, a receiver, a speaker and a microphone.

Paging

With this one-way communications system, an individual or a group of people receives messages by way of personal radio receivers called pagers. The recipients of the messages are unable to respond to the message without going to a telephone. There may be a need to allow contact with only one individual or with a select group of people on these types of systems. In order to accomplish this, a coding system is used where users on the system have a unique ID encoded in their pager. Units will receive the ID before the message and thus only allow the message to pass if the ID matches the one programmed to the pager.

Click on this graphic to animate [75KB]

For efficiency, some organizations suit their individual needs by using combinations of these types of systems. For instance, a central dispatch unit may combine with the unit-to-unit system to enable the mobile users to communicate with one another.

Two-way radio systems can also be connected to the conventional telephone network allowing mobile and portable radios to initiate and receive regular phone calls. This is done by connecting telephone lines to the two-way radio system base station with a device called a patch.
Touch-Code microphones are then used by the radio users to key in the telephone numbers.

Task

This concludes lesson one.

Index
|

Resource |

Glossary |
Outcomes |
Help

© Copyright
NB Distance Education Inc.