HINTS ABOUT OSCILLATION

Evening Post, Volume CXII, Issue 97, 21 October 1926, Page 14

HINTS ABOUT OSCILLATION

Some useful hints have been provided by the engineers at 2LO, the famous London Broadcasting Station, for the benefit of listeners generally and oscillators in particular. They state that oscillation is caused by the mishandling, through ignorance or carelessness, of a valve receiver. If a valve set is tuned in to a station a howl of constant or variable note may be heard in the telephones. This may be caused by another oscillating receiver, or by the set being operated. A simple test which consists of moving the tuning adjustment of the receiver, will at once show whether the set being operated is at fault. If the note varies in pitch sympathetically, with the alteration of the receiver's tuning adjustment, then the receiver is at fault, and the oscillation will cease if the reaction coil be moved away from the secondary until no howl can be heard. Some people tune in a broadcasting station by making the receiver howl at a high pitched note and then, gradually reduce this note until it is by altering the tuning adjustment, so low as to be almost or quite inaudible. They are under the impression that the receiver is not oscillating when no howl is heard, but as a matter of fact it is probably still oscillating at a frequency exactly the same as that of the broadcasting station. This method of zero beat reception, as it is frequently called, is very often practised by the unskilled amateur, but it is productive of distortion both in the receiver itself and in other receivers near it. If an amateur thinks he is working on zero beat he can easily test the fact by moving out the reaction coil slightly. If a howl occurs then the set was oscillating and causing interference. Another test is to touch the aerial terminal, when, if oscillation is occurring, a howi or loud click will be heard.