Hum in Crystal Sets

Radio Record, Volume III, Issue 11, 27 September 1929, Page 27

Hum in Crystal Sets

How to Eliminate It (CRYSTAL receivers, though universally recognised as being troublefree, in remote cases develop an annoying hum in the ’phones, Such interference is probably due to the proximity of (a) a generating station, (b) power mains, (c) a portion of the electric wiring of the house running approximately parallel to the aerial. As removing the cause of the trouble is unfortunately impracticable, any method of eliminating this interference must be developed from the set itself. In most cases, if a moistened fingertip is placed on the earth terminal, the hum will disappear, though upon removal of the finger-tip the disturbance, of course manifests itself once more. However, elimination may be made permanent by attaching a 5ft. or 6ft, length of bare wire to the earth terminal, and by allowing it to dangle upon the floor. Alternatively, this may be attached to a metal plate, or to any convenient metal object in the room such as a brass fender. ; This extra earth connection establishes a means of capacity leakage, and this allows the induced oscillations responsible for the interference to leak away to earth.