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Likewise, by varying the capacitance and the inductance of the receptor the circuits can be tuned to receive incoming electric waves of whatever length within the limitation of the apparatus.
A variable condenser, see C, of the rotating type is formed of a set of fixed semi-circular metal plates which are slightly separated from each other and between these a similar set of movable semi-circular metal plates is made to interleave; the latter are secured to a shaft on the top end of which is a knob and by turning it the capacitance of the condenser, and, hence, of the circuit in which it is connected, is varied.
If your aerial is not very high or long you can use loading coils, but to get anything like efficient results with them you must have an aerial of large capacitance and the only way to get this is to put up a high and long one with two or more parallel wires spaced a goodly distance apart. The Parts and How to Connect Them Up.
As for tuning, just as changing the length and the thickness of the prongs of a tuning fork varies the frequency with which it vibrates and, hence, the length of the waves it sends out, so, too, by varying the capacitance of the condenser and the inductance of the tuning coil of the transmitter the frequency of the electric oscillations set up in the circuit may be changed and, consequently, the length of the electric waves they send out.
The resistance of a circuit to high frequency currents is generally found in the spark gap, arc gap, or the space between the electrodes of a vacuum tube. The unit of resistance is, as stated, the ohm, and its symbol is R. The Effect of Capacitance, Inductance and Resistance on Electric Oscillations.
A variable condenser, see C, of the rotating type is formed of a set of fixed semi-circular metal plates which are slightly separated from each other and between these a similar set of movable semi-circular metal plates is made to interleave; the latter are secured to a shaft on the top end of which is a knob and by turning it the capacitance of the condenser, and, hence, of the circuit in which it is connected, is varied.
An oscillation circuit, as pointed out before, is one in which high frequency currents surge or oscillate. Now the number of times a high frequency current will surge forth and back in a circuit depends upon three factors of the latter and these are called the constants of the circuit, namely: its capacitance, its inductance and its resistance. What Capacitance Is.
The capacitance of a condenser or a circuit is directly proportional to the quantity of electricity that will keep the charge at a given potential. The farad, whose symbol is M, is the unit of capacitance and a condenser or a circuit to have a capacitance of one farad must be of such size that one coulomb, which is the unit of electrical quantity, will raise its charge to a potential of one volt.
The high potential alternating current delivered by the secondary coil not only charges the spark gap electrodes which necessarily have a very small capacitance, but it charges the condenser which has a large capacitance and the value of which can be changed at will.
They have a capacitance of 1 mfd. and will stand 750 volts. These condensers cost about $2.00 each. The Filter Reactance Coil. It consists of a coil of wire wound on a soft iron core and has a large inductance, hence the capacitance of the filter condensers are proportionately smaller than where a small inductance is used which has been the general practice.
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