HOMODYNE AND SYNCHRODYNE

6. Tuning-Whistle Suppression

One new feature which the author incorporated in one of his designs was an effective tuning-whistle suppressor. When the synchrodyne is being tuned-in and the oscillator is not quite synchronised, a very harsh beat-note is produced which approaches zero frequency as synchronism is reached. It is desirable, for comfort in operating the receiver, that …. … to this device is that a small amount of non-linearity is introduced into the audio output by the rectifier network unless the depth of modulation of the r.f. signal is very small; it is therefore advisable to have a switch to cut out the network when the required signal is satisfactorily tuned in. It should be noted that this whistle-suppressing circuit will operate on any signal which may be selected provided the amplitude is sufficient to produce a d.c. large enough to overcome the bias on the rectifiers.