Theoretically speaking, "to match a desired frequency," which will most likely be that of the transmitter's.
That is understood, but I have not a clue how it works. Why is it that when you make a coil with this diameter, this height, & with this AWG of wire, you get a "tuned" coil. Better yet, why is it that when you change these physical dimensions, geometry of the coil if you will, that you in turn change the freq of the coil?
The only logical thing I can think of is the physical dimensions of the EM wave being transmitted. The wavelength. Perhaps the wavelength needs to be equal to the + & - (the ends) of the coil? Think of it as taking a coil & unwinding it. You end up with a specific length. Now that length should be equal to the EM wave?
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That is understood, but I have not a clue how it works. Why is it that when you make a coil with this diameter, this height, & with this AWG of wire, you get a "tuned" coil. Better yet, why is it that when you change these physical dimensions, geometry of the coil if you will, that you in turn change the freq of the coil?
The only logical thing I can think of is the physical dimensions of the EM wave being transmitted. The wavelength. Perhaps the wavelength needs to be equal to the + & - (the ends) of the coil? Think of it as taking a coil & unwinding it. You end up with a specific length. Now that length should be equal to the EM wave?
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There's two ways to tune something in the RF world. One way is to make an LC resonator that resonates at some desired frequency,and another is to make the electrical length of something equal to some multiple of the wavelength of interest.
Every conductor has some inductance and capacitance, and therefore a resonant frequency. Changing the physical geometry of the conductor, like winding it into a coil, alters both of these parameters and can change the resonant frequency. Do whatever you want to the wire. Crunch it into a ball and throw it in the trash and it will be tuned to some frequency, just not the one you want and it won't have a the greatest Q factor.
The electrical length of something is a function of how long it is and how fast a wave propagates through it. For electricity in a conductor, this will always be somewhat slower than the speed of light. The propagation speed will be determined by the series inductance and the parallel capacitance of the conductor. Think of it as a bunch of little inductors and capacitors all strung together(this is the concept of distributed parameters vs. lumped parameters). And the product of these capacitors to inductors determines the propagation speed. The greater the inductance and capacitance, the slower the wave will travel. Changing the size of the wire and how close one winding is to the next changes the series inductance and parallel capacitance.
Every conductor has some inductance and capacitance, and therefore a resonant frequency. Changing the physical geometry of the conductor, like winding it into a coil, alters both of these parameters and can change the resonant frequency. Do whatever you want to the wire. Crunch it into a ball and throw it in the trash and it will be tuned to some frequency, just not the one you want and it won't have a the greatest Q factor.
The electrical length of something is a function of how long it is and how fast a wave propagates through it. For electricity in a conductor, this will always be somewhat slower than the speed of light. The propagation speed will be determined by the series inductance and the parallel capacitance of the conductor. Think of it as a bunch of little inductors and capacitors all strung together(this is the concept of distributed parameters vs. lumped parameters). And the product of these capacitors to inductors determines the propagation speed. The greater the inductance and capacitance, the slower the wave will travel. Changing the size of the wire and how close one winding is to the next changes the series inductance and parallel capacitance.
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If the aerial is tuned it has active resistance at the transmitter frequency. If aerial is shorter than it should be then it has a capacitive impedance. It's bad for the transmitter and for the feeder. To make it active one should add a coil which would make a resonant circuit with the capacitance of the aerial. Diameter and height define necessary inductance of the coil and AVG makes sure that the coil bears current flowing in the aerial
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The value of an inductor depends on the core permeability and the geometry of the windings. If it is an air core this is still true. It has nothing to do with wavelength.