## Short Range Radio Device Communications

### Commission for Communications Regulations

Physics
Technology
Today SRDs or ‘short range (radio) devices’ are in common use. These devices use low power RF (radio frequency) in specified RF bands. They are not likely to cause harmful interference to other networks or to essential public services and so no licence is required for their use.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

### Lesson excerpt

Radios and TVs pick up and process radio waves, i.e., electromagnetic waves typically ranging in frequency from 30 Hz to 30 GHz. Such broadcasts require high power transmitters. Most of the RTE radio transmitters operate at 200,000 watts (i.e. 200 kW) while the power of some local radio transmitters may be as low as 10 watts.

In Ireland (as in most countries) a person must obtain a licence for radio transmission. The type of licence depends on the application (mobile phone, amateur radio, air traffi c services etc.). The licence specifi es the maximum power and the frequency ranges or ‘bands’.

However, no licence is required for certain transmissions that we take for granted today. For instance, a mobile phone must be able to transmit radio signals as well as receive them. Mobile phones operate in specific radio frequency bands and their power is less than 0.4 W.

A smart phone may also have WiFi capability, that is, it uses a specified communications protocol and transmits radio signals at low power (generally less than 0.1 W). WiFi therefore has a short range ― typically less than 100 metres.

What are electromagnetic waves?
We take light for granted. At the flick of a switch we can turn on an electric lamp. The shape of shadows lead us to think that something is coming from the lamp and it seems to travel in straight lines. We can reflect light with a mirror and refract it with a lens. In 1678 Christiaan Huygens explained the properties of light in terms of waves of some sort. In 1690 Isaac Newton tried to explain the properties of light in terms of little particles or ‘corpuscles’ as he called them. However, around 1804 Thomas Young demonstrated diffraction and interference of light — properties that are characteristic of waves. The wave theory of light was then universally accepted. But nobody knew what was actually waving.

In 1831 Michael Faraday discovered electromagnetic induction, i.e the generation of electricity using a magnet and a conductor. Faraday thought that light might have electrical or magnetic properties and after years of trial and error he was eventually successful. He published his findings the following year (1845). This was a remarkable discovery. Indeed, many people today would not expect light to be affected by a magnet.

### True or False?

1. TV signals are in fact radio waves. true
2. The frequency of radio waves ranges from 30 Hz to 30 MHz false
4. SRDs signals are confined to specified radio bands. true
5. The power of SRDs is about 10 watts. false
6. WiFi is a particular SRD application. true
7. Credit card transactions can be carried out using Near-field communication (NFC). true
8. Isaac Newton discovered radio waves in 1690. false
9. Light waves are electromagnetic. true
10. RFIDs can transmit radio signals. true
11. An alternating current produces an alternating magnetic field. true
12. Bluetooth devices transmit on one radio frequency band. false

### Glossary of terms

band
a range of radio frequencies used for a particular purpose
barcode
scannable lines representing data such as product numbers and prices
a radio transmission intended for public access
channels
subsections of a radio frequency band
FM
frequency modulation -- a way of encoding audio signals on a radio transmission
Internet of Things
networking of physical devices such as domestic devices by using smart electronics
Mbps
megabits per second
modulated
modified in a defined way to carry another signal; e.g. amplitude modulation (AM) and frequency modulation (FM)
NFC
near field communication
electromagnetic waves with wavelengths greater than about 1 millimetre
refract
change direction due to change of medium
RFID
short range
communications devices with typical power in the 25 mW to 100 mW range
SRD
short range device
wireless router
a computer networking device that sends and receives data as packets
WLAN
wireless local area network
watt
(W) the SI unit of power. Power is the rate at which energy is transformed.
packets
a block of data
magnetic field
a region of space around a magnet in which it can exerts a force on magnetic material
protocol
a set of rules, e.g. specifying how data should be sent
WiFi
a wireless protocol devised around 1991 as a basis for wireless computer networking
Bluetooth
a wireless protocol used for personal area networks (PANs); it is used to facilitate communication between PDAs, mobile phones, laptops, PCs, printers, digital cameras etc.
carrier
an individual that carries one gene for a particular recessive trait
digital code
Digital data is formatted according in a particular code so that the receiver can interpret the information correctly
alternating current
electric current whose direction is reversed at a fixed frequency known as the mains frequency; the mains frequency in Europe is 50 Hz
GHz
gigahertz; 1 GHz = 1000 MHz or 1000, 000, 000 per second
Hz
hertz; the unit of frequency, meaning oscillations per second; named after Heinrich Hertz (1857 – 1894)
kW
kilowatt, unit of electrical power equal to 1000 watts
electromagnetic wave
radiation, which travels at the speed of light, consisting of electric and magnetic oscillations at right angles to each other; the amount of energy it carries is directly proportional to its frequency (and so is inversely proportional to its wavelength)
interference
the addition or combination of waves; it can be of two types: constructive, in which waves reinforce one another, and destructive, in which waves cancel each other out
diffraction
the bending of waves, when they pass the edge of an obstacle, or through a small gap
electromagnetic spectrum
the entire range of electromagnetic radiation. The spectrum usually is divided into seven sections. From the longest wavelengths to the shortest, these are radio, microwave, infrared, visible, ultraviolet, x-ray, and gamma ray radiation
electromagnetic induction
the inducing of an emf in a conductor when it cuts, or is cut by, lines of magnetic force. The induced emf E is equal to the rate of change of flux, E = d(phi)/dt
power
the rate at which energy is transformed