ВЭФ 12 (Astrad VEF 12 Project) - including a transistor tutorial

[Nowhere-Man]

Back to radios. Here is something more relevant to that capacitor we discussed: AC signal current and capacitors but at resonant frequencies. Example: AC into circuit that has resistor, capacitor and winding in parallel across the lines. Now if the signal is low frequency, capacitor reactance will be higher than XL and AC current will react to the reactances and resistance of the circuit. At higher frequencies, XL will be higher reactance than XC. Yet at resonance both reactances will equalise but the phases cancel. So only the pure resistaance allows current. This is in part similar to what Terry referred to earlier with AC and capacitors. And to add something I just worked out mathematically: series and parallel resistance circuits like this have the same Q if XL and XC (in both circuits are equal and RP (parallel) times RS (series) equals the square of the resonant reactance. See page 43 ARRL