"TRUTH'S RADIO CLUB

NZ Truth, Issue 1096, 2 December 1926, Page 2

"TRUTH'S RADIO CLUB

SOME UNWANTED NOISES

Causes And Their Corrections

(By "Neutrodyne.")

In some instances the undesirable noise^ that sire heard on the loud-speaker or telephones may originate at the broadcasting 1 station, but generally speaking the trouble is found* to be either m the receiving set or between the broadcasting station and the receiver— i.e., m the ether.

A STEADY hiss, which frequently blurs the voice of the artist, may be due to a noisy microphone, and when the music or voice is cracked, as is the case very frequently with the New Zealand stations, the cause of this is, m all probability, due to blasting of the microphone or poor modulation. Relay lines which ' are used for broadcasting programmes picked up from points remote from the studio are often excessively noisy by. currents being induced from neighboring power lines. A rushing sound which is particularly noticeable if the receiver is tuned very sharply »to a station, is caused by the generator supplying the plate voltage to the v transmitting tubes. ' s * This noise is more or less noticeable on all stations, and is heard all „the time the station is on the air. Ether Disturbances • — — ~ — ■ Next to be -considered are noises /#hich are caused by electrical disturbances m the ether between the transmitting station and receiver. There are a number of sources from which these noises arise, a few being high tension power lines, leaking transformers, defective insulators, X-ray and violet ray machines, lifts, and sparking at the brushes of motors and generators. Tramway trolley poles, telephone and telegraph systems, and innumerable other electrical contrivances also cause them. The disturbances which we might say are broadcasted from these sources are usually at short wave lengths and are picked up by a sensitive receiver. Static is caused by atmospheric disturbances and is usually worse m the summer than m the winter months. Probably the most common annoyance experienced m cities is due to improperly controlled regenerative receivers, which -cause a howling note of varying pitch to be heard m the ; speaker. Frequently an excellent programme is suddenly cut off for a short period, or broken . by a series of unfamiliar clicks. These may be traced to key clicks v from a continuous wave transmitter or a near-by regenerative or superheterodyne receiver which is not being controlled correctly. Finally, there are' the noises which are caused by the receiver | itself or the equipment used m conjunction with it. B batteries which have run down cause a crackling noise and sometimes a high-pitched squeal which is' •heard when listening on the second stage. When tlie voltage of a 45 -volt A battery drops to 37 volts it is time to discard tt.

- Valves and Batteries

Storage or wet B batteries often cause, the same trouble, even though the voltmeter reads high, this being due to the fact that a storage battery will usuallk read nearly fun voltage

m spite of the fact that it is almost completely exhausted. A hydrometer reading is the onlytrue method of obtaining a correct indication of the state of this- type of battery. • v , Defective valves afe sometimes the cause of unwanted noises. Although outwardly they may appear quite 0.k., it sometimes happens that their elements are not rigidly, supported, and any disturbance m the vicinity of the receiver may cause these elements to vibrate. This vibration will, cause a feell-like sound which may build up m volume and .drown out the programme. A somewhat similar sound will probably be experienced if the loud-speaker is placed on top of the set or by pointing the horn m the direction of the receiver. This may be remedied by a slight change m the position of the speaker. Noises are also caused by dirty prongs of the vacuum tubes or by sockets which do not make proper contact. Clean the valve terminals at frequent intervals and bend up the contact springs of the sockets.