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Typical Radio/ Wireless Link Structure.

Radio communication above the VHF frequency range (above 150 MHz) uses high-frequency waveforms that cannot be directly processed by A-to-D or D-to-A technology. Hetrodyning is analogue multiplication with a sine wave carrier to perform frequency conversion. This exploits the sin(A)*sin(B) = -cos(A+B)/2 part of the standard trig identity for converting upwards and the other half for converting downwars.

The high frequency circuity is almost always implemented on a separate chip from the digital signal processing (DSP) for the baseband logic.

The radio transmitter is typically 50 percent efficient and will use a about 100 mW for most indoor purposes. A cell phone transmitter has a maximum power of 4W which will be used when a long distance from the mast. (Discuss: Having a mast in a school playground means the children are beaming far less radio signal from their own phones into their own heads.) The backlight on a mobile phone LCD may use 300mW (100 LEDs at 30 mW each).


20: (C) 2008-17, DJ Greaves, University of Cambridge, Computer Laboratory.