Advanced Radio and Radar Part 1 Communicating

Introduction Communication may be defined as “the exchange of information” and as such is a two-way process. It’s the transmission and the receiving that makes a communication. Speech is one method of communication. You need a voice to “transmit” a message (in the form of sound energy) and ears to “receive” the reply.

Introduction However, using sound has drawbacks: a.The speed of sound is quite slow - b.Sound does not travel very far, even if you have a very loud voice. c. Sound can be distorted by outside factors - echoes, wind & other unwanted noises. d. Sound will not travel through a vacuum – it needs a "medium“ to transmit the energy. 300 m/s.

Introduction You can improve the way sound travels by replacing air with a solid material. The string carries the sound better than air – you can speak quietly into one can, and the person holding the other one against an ear can hear you easily.

Introduction The Speed of Sound Is dependant upon the type and temperature of the medium through which it moves. At sea level in dry air at 15°C (59°F), the speed of sound is 340 m/s (1,115 ft/s). BUT At sea level in dry air at 25°C (77°F), the speed of sound is 346 m/s (1,135 ft/s). So the higher the temperature the faster the speed.

Introduction The Speed of Sound Is dependant upon the type and temperature of the medium through which it moves. and at 25,000 ft, the speed is only 309 m/s (1,014 ft/s). While at 250,000 ft, the speed drops to 269 m/s (883 ft/s). So the higher the altitude the lower the speed.

Introduction The Speed of Sound Is dependant upon the type and temperature of the medium through which it moves. in fresh water at 20°C, in fresh water at 20°C, the speed is about 1,482 m/s (4,862 ft/s). and in solid steel, the speed is about 5,960 m/s (19,554 ft/s). But the accepted speed is – 300 m/s And finally...

Electromagnetic Waves While sound works well over short distances, for long-range communications we need RADIO. and for radio we need some form of energy. Electricity can be ‘static’, like the energy that makes your hair stand on end. Magnetism can also be ‘static’, as it is in a common magnet.

Electromagnetic Waves While sound works well over short distances, for long-range communications we need RADIO. and for radio we need some form of energy. A changing magnetic field will induce a changing electric field and vice-versa — and vice-versa — These changing fields form ‘electromagnetic waves’. the two are linked.

Electromagnetic Waves While sound works well over short distances, for long-range communications we need RADIO. When a direct electric current flows in a wire, a magnetic field is produced outside of the wire. DC Direct Current Wire conductor Magnetic field

Electromagnetic Waves When an alternating current flows in a wire, an electromagnetic wave is produced. As before, the current produces a magnetic field, but it is changing strength and direction in sympathy with the conductor’s electric current. AC Alternating Current

Electromagnetic Waves And you can’t change a magnetising force without generating an electric field... e And you can’t change an electric field without generating another magnetic field... B ! AC e e e B B B

B Electromagnetic Waves AC e e e B B e e e B B B This process is ever lasting, forming a perpetual, ever radiating radio wave. Travelling at the speed of light 186,000 miles per second or 300,000,000 meters per second !

Electromagnetic Waves This process is ever lasting, forming a perpetual, ever radiating radio wave. It’s the combination of the magnetic and electric fields that form electromagnetic ‘em’ waves. The frequency of the alternating current determines the frequency of the ‘em’ waves, And the power of the alternating current will govern the range of radiation.

Electromagnetic Radiation A basic radio system consists of - A Transmitter and a Reciever The link from the Tx to the Rx is not sound energy, but electromagnetic (em) energy, - Radio Waves. TransmitterReceiver Tx Y Rx Y

Electromagnetic Radiation The transmitter converts information into ‘em’ radiation, (Sound, Pictures or Digital Code), and transmits in all directions from the aerial. Transmitters come in all shapes and sizes, from TV remote controls of 50 milliwatts, to radio transmitter of up to 500 kilowatts. TransmitterReceiver Tx Y Rx Y

Electromagnetic Radiation Electromagnetic radiation travels in waves. 012 Time in seconds λ Frequency = 2 Hz (i.e. 2 cycles per sec) Amplitude (a) distance from the Amplitude axis to a crest. Wavelength ( λ ) the length of one wave – crest to crest. Frequency (f) the number of cycles in each second. Velocity (v) the speed at which the wave moves. Measured in Hertz Hz Axis Measured in metres, cm or mm Amplitude f 3 x108 m/s (speed of light) = f A number of Units available and has the relationship:

Electromagnetic Radiation One hertz means “one cycle per second” 100 Hz means “one hundred cycles per second”, and so on. Commonly used multiples are - KHz (kilohertz, 10 3 Hz), 1,000 Hz MHz (megahertz, 10 6 Hz), 1,000,000 Hz GHz (gigahertz, 10 9 Hz) 1,000,000,000 Hz and THz (terahertz, Hz) 1,000,000,000,000 Hz.

Check of Understanding Which of the following statements is a disadvantage of using sound for communication? It will not travel through solid materials It will not travel through air It will not travel through water It will not travel through a vacuum

What medium replaces sound for effective long-range communication? Electromagnetic energy Potential energy Kinetic energy Electrical energy Check of Understanding

How many Bean cans would you need for an effective two-way communication system? Four One Three Two Check of Understanding

A radio communications system consists of: A transmitter and receiver. A sender, receiver and interconnecting wires. A transmitting tower and a car, or home radio. A transmitter, loudspeaker and interconnecting wires. Check of Understanding

50 cycles per second 5,000 cycles per minute 5,000 cycles per second 50 cycles per minute Check of Understanding A wave has a frequency of 5 KHz. What does this represent?

The less efficient it is. The lower the optimum frequency that it will transmit and receive. The higher the optimum frequency that it will transmit and receive. The more efficient it is. Check of Understanding The shorter the length of an aerial becomes:

A few more questions. 1.What is the approximate speed of sound? 2.What is the Speed of Light? 3.What is meant by Amplitude? 4.What is the rough power range of transmitters ? Check of Understanding

Advanced Radio and Radar End of Presentation