RADIO WAVES

& MICROWAVES

TRANSMITTER RECEIVER

An AC CURRENT is fed into the transmitter

Makes ELECTRONS in the METAL TRANSMITTER

AERIAL OSCILLATE

Which produce RADIO WAVES

Which make ELECTRONS in the METAL RECEIVER AERIAL OSCILLATE

And a matching AC CURRENT comes out of

the receiver

TRANSMITTER

RECEIVERS

RADIO WAVES are used for…..

Studying the

Universe

Carrying information

Control signals

Navigation and radar

The Radio Spectrum

LW MW SW

LF MF HF VHF UHF SHF

300 kHz 300 MHz3 MHz 30 MHz 3 GHz

1 km 1m100m 10m 10 cm

RADIO STATIONS& Navigation beacons

TV, remote controlled toys,

garage doors etc

Mobiles, m’wave ovens, wireless,

satellites

Radar

LONG WAVE radio signals can ‘bend around’ the curve of the Earth’s surface and so have a LONG RANGE.

ionosphere

reflections from the ground

MEDIUM WAVE radio waves are reflected by a layer of charged particles (ions) in the upper atmosphere called the IONOSPHERE.

Reflections from the ground can give a very long range, but the ionosphere has several layers whose height and density change making reception very variable

SHORT WAVE (microwave) radio waves pass through the ionosphere to space and so can be used for satellite relays, which can pass a signal around the world

ANALOGUE AND DIGITALRadio and TV signals were carried by ANALOGUE radio wave signals.

These are now being replaced by DIGITAL radio wave signals.

1

0

An ANALOGUE signal can have any value

Eg 0.02, 0.47, 0.53, 0.85, 0.79, 0.33, -0.14, -0.38

A DIGITAL signal can only be ON or OFF (0 or 1)

Eg 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1

DIGITAL SIGNALS:• Carry MORE INFORMATION in the same time• Don’t suffer from INTERFERENCE, so give clearer sound & pictures• Are easy to STORE on PCs, CDs, DVDs, MP3 players etc

The ‘gaps’ are 1s and the ‘pits’ are 0s

The gaps reflect the laser and the pits don’t

pitgap

Why are digital signals not affected by interference?

Whenever a signal travels (through a wire or as waves through the air), two things happen: it gets WEAKER and it picks up NOISE

GETS WEAKER

PICKS UP NOISE

ANALOGUE DIGITAL

AMPLIFIER

DIGITAL signals use an amplifier called a REGENERATOR which just decides whether the signal is a ‘0’ or a ‘1’ and then recreates it.

(original)

REGENERATOR

If we use an amplifier to make an analogue signal stronger, the noise is amplified as well. (Turning up the volume on a crackly station doesn’t help!)

MICROWAVES

Microwaves are VERY SHORT WAVELENGTH RADIO WAVES.

Main uses:

COMMUNICATIONS COOKING

Communications: satellites

As microwaves pass through the ionosphere, they can be used to send TV, Internet and mobile ‘phone signals up to a satellite which then relays them around the world

Mobile phones are portable microwave transmitters and receivers combined in one handset.

All phone companies are part of the world wide GSM* network

*Global System for Mobile communications

A mobile communicates with base stations by microwave signals. Base stations can be powerful transmitters that cover large areas of countryside or weaker transmitters for small areas of towns

Base Station

Exchange Internet

Landline network

Satellite Relay

Exchange

Satellite Relay

Microwave

Cable

Base Station

Base Station

The GSM network can pass information around the world in a fraction of a second

A mobile is constantly sending out short microwave signals to find the nearest base station to get the best signal. The phone companies (and the police) can locate where the phone was at any time from records of how these signal change.

mic

rowav

es

Cooking:

Microwaves with just the right frequency (2,450MHz) can make water molecules strongly vibrate. This heats up objects containing water as energy is transferred from the microwaves to the water molecules

In a microwave oven, objects containing water heat up all the way through. Objects in normal (infra red) ovens heat up from the outside first. Temperatures of test tubes of cold water in a microwave and

in a normal oven after 1 minute

Water HOTGlass tube cold

Glass tube hotWater still cold

Are Mobile Phones a Health Risk?

Although the microwave transmitters in phones are much less powerful than in microwave ovens, phones DO transfer energy to the tissue in the head when the phone is being used.

The question is does this cause damage?

Many studies have looked at:

• The effects of weak microwaves (same strength and frequency as phones) on laboratory animals

• The effects on people who described their mobile phone use to the scientists

Researchers in Sweden have found that just two minutes' exposure to energy waves from a handset can disable a defence mechanism in the body designed to prevent harmful proteins and toxins in the blood from entering the brain.

Once the proteins enter brain tissue there is a higher risk of brain and nerve diseases such as Alzheimer's, Parkinson's and multiple sclerosis developing.

Other effects reported include:

Skin and brain cancer

Cancer of the middle ear

Damage to DNA in cells

Damage to the immune system

Other ‘nervous system’ effects

Tests on lab animals and on tissue samples

This research was carried out on 16 people who had complained of symptoms from using mobile phones.

It was found 13 suffered symptoms including nausea, headaches and dizziness which researchers believe are a clear indication of radiation. IDEA chairman Dr Philip Michael said: "This is causing disabilities in a large section of the population. "We are working on funding for a far larger study which will use blind testing to prove beyond doubt that mobile phones are responsible, but we believe the evidence is now overwhelming.

“The brain is an electrical instrument, and the frequency of radiation produced is very close to that used in the brain, so it's no big surprise to find a phone is interfering with that frequency, causing headaches, nausea and the other problems." Tests on

people

Federation of the Electronics Industry:

"We firmly believe that there is no link between use of mobile phones and any adverse human health effect.

"This is based on many years of research. The mobile phone industry is a global industry and research into the safety of phones is done on a global scale - probably $60m has been spent on this particular issue”.

“The Government set the guidelines that the industry follows, and all mobile phones sold in the UK are designed, built and tested to these standards which take account of all the scientific research into this issue”

The Phone Companies say:

A government-funded committee headed by scientist Sir William Stewart concluded that while there was no direct evidence of a health risk from using mobiles, more research was needed to prove their safety.

The chairman said: "I don't think we can put our hands on our hearts and say mobile phones are safe. If there are risks, and we think there may be risks, then the people who are going to be most affected are children."

He advised people to limit the time they spend on their mobile, and to try to stay away from mobile phone masts.

The Government says:

HOW CAN YOU REDUCE YOUR MICROWAVE DOSE?

HIGH SIGNAL STRENGTH LOW

Microwave oven

Mobile mast (20m away)

Mobile phone

Cordless phone

Bluetooth headsets

You will get a bigger dose if:

The transmitter is CLOSE to your head

You use the device for LONGER

1. USE YOUR PHONE FAR LESS (most effective)

2. Use a hands free kit for conversations but NOT A WIRELESS ONE!

x

3. SEND TEXTS rather than talking as the phone only transmits for a few seconds to send one

4. Keep the phone away from your head when it is DIALLING OUT as this is when the signal is strongest.

5. Make sure you use a CORDED landline for long conversations NOT a CORDLESS model.

x

x