HINTS ABOUT OSCILLATION

Evening Post, Volume CXII, Issue 49, 26 August 1926, Page 14

HINTS ABOUT OSCILLATION

Some exceedingly 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 valvo 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 simplo test which consists of moving the tuning adjustment of the receiver, will at once show whether thetset being operated is at fault. If the ntfte 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 socondary 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, by altering the tuning adjustment, gradually reduce this note until it is 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 rat the reaction coil slightly. If a howl occurs then the set was oscillating and causing interference. Another test is to toueli the aerial terminal, when if oscillation is occurring a howl or loud click will bo hoard.