The ‘Wave Band’ Theory of Wireless Transmission

Abstract

SIR AMBROSE FLEMING does not give us in his very able article any alternative explanation of the fundamental problem of the tuned circuit, namely, that the really selective circuit does cut off the higher audio frequencies, generally explained by the ‘cutting of the side bands’ What is actually happening? Does not the solution lie in the fact that the damping of a resonant system falls off as its selectivity increases? In our modern lightly damped receiver, the oscillation persists long after its excitation has ceased. If it is excited by a carrier modulated by a high audio frequency, the persistence of its vibrations will not allow the amplitude of these to vary with the modulated amplitude of the incoming wave and the modula tion gets flattened out, whilst with a low modulating frequency, or bass note, the slower rise and fall of the carrier amplitude gives time for the circuit oscillations to rise and fall with it and thus give a faithful reproduction.