How does a radio filter out waves of different frequencies?

March 5th, 2012

Question by : How does a radio filter out waves of different frequencies?
How does a radio filter out waves of different frequencies?
With all the different frequencies of waves in the air, how does the sound out of a radio come out clear?What do I need to make one?

Best answer:

Answer by Electronics is my hobby
dear radio does not filter any waves!! let me explain..
Radio has a demodulator in it. it is a PLL. now the demodulator ics like MM74HC4046 are connected in a standard circuit. when you tune the radio for a frequency, which is actually changing the resistor values for the oscillator, you demodulate the frequencies one by one. supose your range is from 300 KHz to 10 MHZ then as you turn the knob, and your circuit has range 300KHz – 12 MHZ thn your starting freq is 300KHz. then as you turn the knob you increase or decrease the resistance and start tuning the circuit. then your first station is at 598khz. at that freq u hear the channel. then as you turn along it goes higher. at 3.9MHZ you listen to different channel. so thats no problem. also the PLL is there which gets locked at a frequency and so there is a conitnuous demodulation at this frequency. I’ve already told you one ic and there are many others. also another is 7046.
if you want ot make one then search FM demodulators by 4046 and use the MM74HC4046. it gives higher selection from short wave, medium wave and FM also.

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One Response

  1. Randy G says:

    A variable capacitor and an inductor are arranged as a filter circuit that passes only one frequency, and cancels out the rest.

    When you turn the know on the radio, you cause moving metal plates to move past each other, which changes the value of the variable capacitor.

    …The simplest tuner consists of an inductor and capacitor connected in parallel. The capacitor is usually made to be variable (although the inductor can made variable it requires a more complex mechanism and is rarely used). This creates a resonant circuit which responds to an alternating current of one frequency. In general, radio makers will use a rule of thumb of 1.5 picofarads per metre wavelength. Common inductance values are 4.1 milliHenries for long wave, 370 microHenries for medium, and 130 nanoHenries for VHF (FM) between 88 and 108 MHz. In a superheterodyne radio the capacitor that tunes the “tank” will be ganged with another; this alters the local oscillator to provide a constant intermediate frequency. Combined with a detector, also known as a demodulator, it becomes the simplest radio receiver, often called a crystal set…

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