What is Radio ? Justin Champion Room C203, Beacon Building Tel 3292,

Content  Introduction –What is Radio –Sine wave –Modulation –Interference  Conclusion

Radio Frequencies  We use this technology everyday –This course would be a lot shorter with out them!  They allow for –Cellular Devices –Wireless Networks –Television –Radio Microphones –Satellite Communications –DECT Telephones –Personal Radios –The full name is Radio Electromagnetic Spectrum, but we use the shortened term Radio

Radio Frequencies  Radio is an electronic magnetic wave –Connect a wire to a battery and touch the ends close to an AM radio  You should hear the sound which is produced –The magnetic pulse which is transmitted will be picked up on a nearby wire as electricity and converted to sound.  By touching and letting go you can produce Morse code over the radio!  The distance this will be picked up by is related to power in the source

Radio Frequencies  To transfer information a carrier wave is required. –On/Off carrier would look like this –More Common is the Sine wave  This changes its value continuously 1 Cycle

Radio Frequencies  Sine Wave –As we know what the carrier wave should be showing  It is easier now to check for changes –These changes will be used to encode information –Carrier wave will also allow for information to be transferred over greater distances  Without errors 1 Cycle Amplitude

Radio Frequencies  Frequency –This refers to how often the Sine wave cycles up and down per second  1 cycle = Hertz (HZ)  1,000 Cycles = Kilohertz (KHz)  1,000,000 cycles = 1 Megahertz (MHz)  1,000,000,000 cycles = 1 Gigahertz (GHz)  Encoding Data –Adjustments to this Sine wave can then be used to encode 1’s and 0’s, voice or video –These adjustments are referred to as Modulation

Radio Frequencies  The following are all radio waves –X-Ray, Light, Gamma Rays –For our normal interest of Radio we use  Very Low Frequency (VLF) –3-30 KHz  Low Frequency (LF) –30 – 300 KHz  Medium Frequency (MF) –300 – 3000 KHz  High Frequency (HF) –3 – 30 MHz  Very High Frequency (VHF) –30 – 300 MHz  Ultra High Frequency (UHF) –300 – 3000 MHz

Radio Frequencies

Radio Modulation  Modulation of the signal –Changes which can be made to a carrier wave  Frequency Shift Keying (Frequency Modulation (FM)) –Increases / decreases the cycling rate of the sine wave  Amplitude Shift Keying (Amplitude Modulation (AM)) –Changes the power of the signal  Phase Shift Keying –Changes the phase that the sine wave is in

Frequency Shift Keying (“Les modulations de base”, 2004, Franck/Pages/Les_modulations_de_base.htm) (“Les modulations de base ”, 2004, Franck/Pages/Les_modulations_de_base.htm) Franck/Pages/Les_modulations_de_base.htm Franck/Pages/Les_modulations_de_base.htm

Amplitude Shift Keying (“Les modulations de base”, 2004, Franck/Pages/Les_modulations_de_base.htm) (“Les modulations de base ”, 2004, Franck/Pages/Les_modulations_de_base.htm) Franck/Pages/Les_modulations_de_base.htm Franck/Pages/Les_modulations_de_base.htm

Phase Shift Keying (“Les modulations de base”, 2004, Franck/Pages/Les_modulations_de_base.htm) (“Les modulations de base ”, 2004, Franck/Pages/Les_modulations_de_base.htm) Franck/Pages/Les_modulations_de_base.htm Franck/Pages/Les_modulations_de_base.htm

Radio Modulation  Bits Encoded –The previous methods allowed for the encoding of 1 bit at a time  Multiple Bits Encoded –Quadrature Phase Shift Keying (QPSK)  Allows for 2 bits to be encoded each modulation.  This technology is used in the IEEE x standards

Radio Modulation  QPSK Modulation –Adjusting the phase puts the signal into one of the quarters

Radio Modulation  Modulation –More than 2 bits can be encoded by encoding phase and amplitude changes  The more bits that are encoded the more susceptible to errors the signal will be  Quadrature Amplitude modulation (QAM) –4 bits  64 QAM –6 bits

Antenna Size  Optimum Antenna Size –4 phases of the carrier wave –Speed of Light is 299,792,458 meters per second –At a frequency of 20Mhz (20,000,000 Hz)  Each cycle takes (1/20,000,000)/4 =  Speed of light * each cycle =  Antenna size of 3.74 meters !

Antenna Size  Optimum Antenna Size - Change this to 900 MHz –4 phases of the carrier wave –Speed of Light is 299,792,458 meters per second –At a frequency of 900MHz (900,000,000 Hz)  Speed of light * each cycle gives  Antenna size of 8 centimeters

Radio Frequency - Authority  Allocation of use –In the UK OFCOM is responsible for allocating licenses for use of the radio spectrum –They allocate all of the civilian uses of the spectrum  –List of recently awarded uses of the radio spectrum  wards wards wards –Military portion of the spectrum is controlled by the Ministry of Defence

Radio Frequency - Authority  Frequency spreading –Unfortunately no one country can control radio waves as they travel until they have no power  The International Telecommunication Union (ITU) based in Switzerland working the United Nations holds regular meetings to agree across countries what frequencies to allocate to what  Signal are difficult to contain within an area

Radio Frequency - Authority  Frequency spreading –Consider this when you are sending your credit card details  You may be in a building  The signal will travel outside of the building –Unless the building has been specially built to deal with this  Someone standing outside will receive these signals –If they are not encrypted in some manner the information is plainly available  ( 2003)

Radio Frequency - Modulation  Problems with Radio Signals –Interference  Any signal which is on the same frequency is interference  Even though to other people it may be a valid signal ! –Bluetooth and b working in the same area is a example

Radio Frequency - Modulation  Interference –Unless something physical blocks the signals will travel in all directions the same distance

Radio Frequency - Modulation  Interference –Continued  It is difficult to predict who far a signal will travel  A lot of factors impact on the radio signal –Frequency used  In general the higher the frequency the shorter the distance travelled  The higher the frequency the more information you can encode per second  The higher the frequency the more the signal resembles the effects of light! –Weather  Outdoor the weather can effect the signal, with heavy rain increasing the attenuation on a signal –Physical Attributes  Signals will have reduced power when passing through physical items, like walls, trees, safety windows being particularly bad !

Radio - Attenuation  Attenuation –The distance travelled by a signal is related to the power  There will still be a maximum effective distance for the communications –After this point more errors will be received than valid data. Time / Distance Strength Power

Conclusion  What we have discussed –What is radio –Radio Frequencies –Sine Waves –Modulation –Interference