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Radio Communication

Radio Communication. SL/HL – Option F.1. Radio communication includes any form of communication that uses radio (EM) waves to transfer information TV, mobile phones, wireless internet, satelite radio. Radio Waves. Electromagnetic wave that is created by an alternating (AC) current

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Radio Communication

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  1. Radio Communication SL/HL – Option F.1

  2. Radio communication includes any form of communication that uses radio (EM) waves to transfer information • TV, mobile phones, wireless internet, satelite radio

  3. Radio Waves • Electromagnetic wave that is created by an alternating (AC) current • Made up of perpendicular electric and magnetic fields

  4. Radio communication • Principle • A changing electric field must be created in order to produce a radio wave • Simplest oscillating circuit is made up of a coil of wire and a capacitor • The circuit will oscillate at a given frequency based on the turns in the coil and the size of the capacitor • When the electrons oscillate, the waves are sent out in all directions • This is called a transmitter

  5. Radio Communication • A second oscillator circuit, placed away from the transmitter will detect the signal • Electrons in the circuit will respond to the EM waves and an alternating current will be produced • The amplitude of this oscillation is generally very small compared to the sent signal

  6. Modulation • In order to send information we need more than just a signal • A single signal frequency would just be a tone • The frequency needs to be changed or modulated to represent the change in data to carry an actual signal • Morse code was simply turning the signal on and off

  7. Modulation • Amplitude and frequency modulation are accomplished by superimposing a second wave upon the first • Carrier wave • original wave • Signal wave • superimposed wave

  8. Amplitude Modulation • The frequency of the carrier wave is constant • The signal wave is used to vary the amplitude of the carrier wave

  9. Sidebands • When a carrier wave is modulated by a signal wave, 2 additional wave are actually produced • This can be shown mathematically but it is not necessary at this point • The 2 additional frequencies are then:

  10. Sidebands • This produces what is known as a power spectrum • A chart showing the different frequencies that make up a signal • Scale is in decibels which is a logarithmic scale so an increase of 1 bel means the power has increased by a factor of 10

  11. Bandwidth • Signals, especially more complex ones (radios) often need more than one frequency to transmit information • With these and their sidebands, a band of frequencies gets taken up by each signal, this is known as bandwidth • Radio stations are allocated a 9 kHz bandwidth • Phones are give 3 kHz • Analog TV signals get 6 MHz since they need to transmit video as well

  12. Frequency Modulation • The amplitude of the carrier wave is kept constant • The signal wave is used to vary the carrier waves frequency

  13. Frequency Modulation • In an FM signal, the carrier wave deviates from its original frequency f by an amount Df • This is known as the peak frequency deviation • So the maximum and minimum frequencies of an FM signal are:

  14. Frequency Modulation • An FM signal also has a modulation index • If the carrier signal f is modulated between f1 and f2 then: • The larger the modulation index of an FM wave, the more sidebands are produced and the wider the bandwidth • In FM signals the bandwidth is equal to:

  15. Comparing AM and FM • Bandwidth • AM uses 9kHz per channel while FM uses 200 kHz • This means that FM stations are farther apart and also why they use higher frequencies • Range • AM signals have a much larger range than FM due to the lower frequencies • AM waves are reflected off of the ionosphere while FM signals shoot off into space

  16. Comparing AM and FM • Quality • Other sources of EM waves, which are all around us, affect AM waves much more significantly • This is why AM stations are more susceptible to noise • Cost • A simple AM receiver can be built very cheaply, while FM receivers are more complex and costly

  17. AM Receiver • Aerial – the antennae, a long conducting rod that EM waves can oscillate electrons in • Tuning Circuit – A circuit that can be ‘tuned’ to resonate at a particular frequency • r.f. (radio frequency) amplifier – amplifies the tuned signal • Demodulator – removes the carrier wave from the signal • a.f. (audio frequency) amplifier – amplifies the audio signal • Speaker

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