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Hi,

I've been studying about electronics for about 8 months. I have a question about tunning a radio. Tunning a radio is usually done by a variable capacitor or variable inductor. Why can't u tune using a variable resistor. They are much cheaper and smaller.

Thanks a lot

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The capacitance of any diode changes when the reverse voltage across it changes. Varactor diodes look like ordinary diodes but are designed to have certain amount of capacitance and the capacitance changes quite a lot when the voltage is changed.
Car radios, VCRs and TVs use varactor diodes for tuning.

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Thanks Audioguru,

Since the topic is tunning(radio), I recently found an old audio/radio system for TV. The Volume control knob said  :o motorized volume. I took it apart, and I think I saw motor. I'm not sure how this thing works?  ???



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Hi


Thanks Audioguru,

Since the topic is tunning(radio), I recently found an old audio/radio system for TV. The Volume control knob said :o motorized volume. I took it apart, and I think I saw motor. I'm not sure how this thing works? ???






the motor acts simply as your hand
i have a remote controlled cd, when i press the + or - volume i can see the volume nob rotate
it is connected by a motor rotate in two direction as the polarity applied on its terminals

For the Varactor diodes, i can add to what my big friend guru said that its capacitance is inversely propotional to the applied voltage; whev v high , c is low so the tunned freq is high

good luck
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Hi Walid,

Thanks!

Probaly that was why. When I bought the system, there wasn't a remote control, but there was a infared detector inside ???. When I saw the motor, and the words, no one would probaly know what it was used for unless they had a remote control  :).
Now I know one more part I can salvage from this system, and it would still work  :)

I have already salvaged some input jacks, and an infared detector, now a motor is on the way soon.....  ;)

Thanks  :)

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