ELIMINATING NOISES

Radio Record, Volume I, Issue 12, 7 October 1927, Page 15

ELIMINATING NOISES

The following talk by Mr. Preston B. Billing, of the Wellington Amateur Radio Society, was delivered through Station 2YA -recently: Noises within your radio receiver are due to one or the other of the foliowing causes: Crackling noises often mistaken for statics are due to defective or runflown. B batteries. If anv one of the 15 or 30 cells: are run down or polarised, amplification of the resulting voltage fluctuations cause crackling in the Jondspeaker. In order to determine if the batteries are really run down or defective, one can substitute another batterv and note if there is anv improyement in the reception, Batteries which show less than 75. per cent. of. their initial voltage shonld be regarded as suspicious. The next place to look is in the A battery, If dry batteries are in tse in this part of the set, the remedy ts fairly obvious they should be replaced. The accummuiator type of A battery does not as a rule give any tronble if the battery is kept well charged, and it is not very old, there should be no tronble from this source. Very often noises will be encountered through a defective grid leak; try one or two leaks and see if there is any improvement. All wiring in the set should be rigid, and connections securely made; flux of any description should be cleaned away immediately the soldering of the joints has been effected. If plug in coils are in use weke certain the plugs are clean, and make contact with their respective sockets. Very often these noises can be traced to bad contacts at the base of the tube sockets, or in the case of the later sbyle of sockets on the side of the valve pins. Sometimes the withdrawal and reinsertion of the valves will clear away the obstruction. If this fails the valve prongs should be cleaned together with the springs of the valve sockets. Bad tubes are frequent offenders, and one would be well advised to make certain of this factor. The noises from this cause are usually more violent, exhibiting themselves as a violent break in the circuit. ‘Ihe trouble is usually due to leakage or to a poor connection between the pins in the base of the valve, and the elements to which they are connected, namely, the grid ind the plate. The filament usuallv oes not give anv trouble, and if no flickering is observed they should be all right. Audio-frequency transform: ers with defective insulation, especially between the primary and frame, and between windings (the primary and secondary), cause noise. Microohonic noises are due to the valves themselves; firstly, the valve seckets should he sprung in order to eliminate noises arising from people walking about the oon, and also to prevetit noises, due to the operator of the set touching the dials in the tuning process. Tf von are in doubt as to whether or rot vour receiver is the cause of the noise, remove the aerial terminal, the set should be nerfectly aniet. and onlv " Slight hiss should Le heard from the valves themselves. THE RADIATION TROUBLE. Speaking of noises leads us to a further problem, and a very annoying one ut that. JI am speaking of radiation. This form of trouble seems to be on the increase, and before closing I would like to say a few words about it. If 1 have received one request to say something of this matter, I have received dozens, especially in the last few days. Now the atmospheric conditions have not been too good during the last week, and possibly there have been listeners straining their sets in order to hear distant stations. ‘This in itself is bad enough, but listeners sliould realise that on nights when the static is bad there is no hope of receiving distant satisfactory reception. Why, then, all this straining to bring them in? All that is happeniug is that your set is adding to the din already manifest. Now, of course, there are some types of set which do not radiate, and it is high time some listeners gave their sets a look over so that their next door neighbour may enjoy the concerts also. In purchasing a set you should obtain an assurance that the receiver will not radiate. Dealers have been instructed that they are not to offer for sale receivers which offend in this respect. Most of the trouble from this cause is due to the constructor himself. He purchases a promising kit of parts, assembles and wires it himself, and then commences to drag in the stations without neutralising his set correctly. The net result is that he secures indifferent reception. What he does get is of a distorted nature, but right apart from this his fellowlisteners are compelled to listen to the awfnl squeals and howls which emanate from their loudspeakers and phones, and which finally compel them to close down altogether. On the other hand, there are some constructors (amateur) who cat asseinble and operate a re. ceiver, taking care to adjust it so that it will cause no annoyance. I would be far better for the listener tc have his set tested for radiation, and thereby eliminate a lot of unpleasant noises, , . My next talk will have more to da with this matter, and I will endeavour to explain how you can ascertais for yourself whether or not your receiver is oscillating, and what is best to be done with it.