RADIO+TUNING+-+SEUNG-HYUN

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Electrical resonance of tuned circuits in radios that allow individual stations to be picked up. Electrical resonance occurs in an electric circuit at a particular resonance frequency where the imaginary parts of circuit element impedances cancel each other. In some circuits this happens when the impedance between the input and output of the circuit is almost zero and the transfer function is close to one.

A resonant circuit consists of an inductor, represented by the letter L, and a capacitor represented by the letter C. When connected together, they can act as an electrical resonator, a storing electrical energy oscillating at the circuit's resonant frequency. Most common application is tuning. For example, when we tune a radio to a particular station, the LC circuits are set at resonance for that particular carrier frequency.



Here is a diagram of the carrier wave of a radio station. As you can see it repeats, first creating a growing positive voltage and then reversing to create negative voltage before starting the whole cycle over again. Radio waves travel at a constant speed of 300,000,000 metres a second. So if the voltage went round the full voltage cycle of starting from zero, positive swing, back to zero, negative swing and finally back to zero in one second, the wave would have travelled 300,000,000 metres in that time and that would be the length of the wave. The faster the rate of vibration the shorter the wavelength of the electromagnetic wave.

Every aerial has a natural frequency it tunes. The longer the aerial the lower its frequency of reception will be. The aerial will capture signals from many different wavelengths, the strength of the signal being much higher near its natural reception frequency and much less at other frequencies.

The signal which would give the strongest voltage response to my aerial would be one four times longer than the wire, making it resonant at a quarter of its wavelength. So listening directly to the output from the aerial I would hear the strongest signal which would be any broadcast station with a wavelength of 96 metres, or frequency of about 3 Mhz.