Basic Radio is a free introductory textbook on electronics based on tubes. See the editorial for more information....


Author: J.B. Hoag

The fidelity of a receiver is its ability to reproduce in its output the wave-form of the modulations which were superimposed upon the carrier wave at the transmitter. A receiver which did not amplify the high-pitched notes to the same degree as the low-pitched notes would sound "boomy", whereas, if the reverse were true and the low-pitched notes were incorrectly suppressed, the high pitches would make the reception sound "tinny". For phone reception, then, the selectivity curve should ideally be such that equal intensity signals over the entire audio range would give the standard signal output. This ideal, however, need not be fulfilled in practice, because, especially with speech, most of the energy in a sound wave is carried in the lower frequency range. For example, the average peak of energy of a man's voice in speaking is around 130 cycles per second, while that for a woman's voice is around 300 cycles per second. Therefore, the rounded curve of Fig. 32 E is permissible in practice. With c.w. reception, these considerations do not apply and the resonance curve can well have great sharpness.

Last Update: 2009-11-01