FOR THE GOOD OF RADIO

Evening Post, Volume CVII, Issue 140, 14 June 1924, Page 22

FOR THE GOOD OF RADIO

CANNOT WE CLEAR THE AIR?

It is a curious fact that among. all the inquiries sent to this office regarding wireless matters, not orie has referred to trouble with regard to selfoscillation of a ■ receiving set. ■ Nobody has written complaining that his reception 'of local concerts ■is poor, except some who have had such weak reception that grave constructional defects were •to blame. Yet, judging by the amount ot interference constantly going on, there must be much room for complaint of just this nature.

The ideal is to have no radiating receivers. But this ideal will not be reached for a long time. Those who own regenerative sets which are: potential sources of interference are desired, in the public interest, to use them so as not to create a disturbance.- Many of these ■ sets are iii the hands of young operators, whd, do not realise the trouble they are causing, and their friends, if they are aware of such cases, will he doing a kindly act and a public service by helping them into the broad way\of radio righteousness.

' "Grid-Bias" is anxious to help cure this grave defect in the wireless community of Wellington, because it is not only a present nuisance; it is a menace ti a hobby which is now entering upon the most hopeful stage of its existence. He; has no desire to preach, but ■ the condition demands it. Hence this

OPEN LETTER TO THE LISTENER.

The future of broadcasting in. New Zealand depends as much upon you as upon the wireless trade or the broad- , casting organisations. If there is broadcasting1 at aIL/-the people who carry it on are obliged, by. commercial interests as ■ well as by their legal undertaking, to do their best.- They are expected, by you among others, to provide ;as good programmes as they can, to use as efficient apparatus as they can as efficiently as • they can, and so to produce effects which listeners can enjoyAt Hint point their duty ends. But the listener has a duty, too. Ho is not obliged /to listen.- He •is ' not obliged, if he does listen, to' adjust his apparatus so that lie enjoys the music. But he is obliged, morally as well as legally, to use his receiving. set so as not to ' interfere wit'ft other people's enjoyment. There are apparently many listeners who do not realise, this; ,and who do not realise that their carelessness may have-disastrous results for the whole community of listeners. .It is quite possible for one wireless listener to ruin the<■ enjoyment'of hundreds/ of others in his neighbourhood. If this* happens here- and .there throughout a populous area, and there is no redress, what is going to happen to radio as a hobby? It will lose its popularity; broadcasting will become, impossible; and one of ,the most attractive of modern p.astimes will be killed.

■ How can this be prevented? Not by force; only by good-will. No legislation can compel, every wireless user to be of good behaviour; and the need for compulsion should not arise. Wireless as ,aa entertainment is within the reach of all classes; but it is good enough for the King. He listens in at Buckingham Palace. Let us all, therefore, keep it good enough for the least of us. •

In, .only one way does the . listener spoil broadcasting, and he can tell quite easily when he is .doing it.' He does it by letting his valve set "oscillate'1' on the wave-length of a transmission. Simple crystal sets cannot cause interference in this way, though they suffer by it. * i ' ■'.

It is very easy to tell whether your valye set is oscillating. "When listening to a broadcast or other radio telephony, the speech or music, whether,loud or not, should be clear and natural, not '.'fuzzy" or . "drummy" or 'mixed with squealing or roaring sounds. If you hear a squeal,' and altering the tuning of the set changes the ■ pitch of the note, your set is oscillating. If, on the other hand, the changed tuning leaves the pitch of the squeal or other interference -unchanged, and only, alters its strength, the trouble is caused by. someone else, and you are experiencing the evil which this is written to cure.

The receiving set will oscillate,without squealing. It only squeals when it is tuned to nearly the same wave length' as^ other waves which strike the aerial. "Silent" oscillation can be detected in various* ways : by the increased loudhess of "atmosphSHcs" ot "statics"-; by the increased loudness and changed tone of any spark morse signals that are heard (these lose their character and all ' sound alike); and, best of all, by touching the grid terminal of each valve with a damp finger. If the set, is not oscillating, there will be a.- ''pop" in the when the. finger'touches, but none when it is removed: If it ia oscillating, the touch pop. will be much louder, and will be followed by another' when the finger is.removed. It is not . always convenient to.. reach these ter- ■ minals, but an equally, good test^ so far as the prevention of interference is concerned, is to touch, with the -wet\ finger, the aerial terminal of the xeceiver. This will'npt always show whether the whole set is'free from self oscillation; but it will show, by the popping sound in the head phones, when the aerial circuit is being oscillated. ■ Tliat iis the state in which waves capable of causing the interference are being radiated. ' . Now the oscillating s^tate has its uses. It enables spark Morse signals to be. heard when they are too^ faint without it. It is essential for ; the reading of continuous wave telegraphy, the. chief method of signalling among amateurs; and it; is. useful; amd often necessary, for picking up telephony from distant stations by finding the "carrier wave.1'1 But it is absolutely, useless for the actual reception of telephony except in special cases,, and with very skilful manipulation. It is not necessary, for the find* ing of ai broadcast when one is within ten miles of. the broadcasting station,and it should not be ueed for that purpose. '• . ■' )

. Whenever a set falls- into oscillation on a broadcast wave-length and causes a squeal, remember that you are not the only one. that, hears it. Listen to the squeals you can hear from other sets, and make up your mind not to add to them. Stop the 'oscillation. Move the_ reaction or tickler coil back ti.l the oscillation, stops, or reduce the .filament brilliancy, or do both. Adjust the grid leak if necessary— this may result in a^great increase of signal strength. Do it with the minimum of reaction, and increase or, reduce the leak till the sounds are at their best. Co not start with too mucll reaction and reduce it.; work the oilier,way. Whate.ver'you do, do not "juggle the ■dials" with the sot oscillating. This makes the.interference more aggravating still. It is bad enough 'when it is done on thy tuning of a strong local broad-

cast, but when it is done on the wavelength of a' distant station, it is much worse. People who are listening to Auckland or Dunedin are usually particularly anxious to hear well, and they have to tune carefully to do it.. Their occupation deserves respect. Anyway, dial-juggling never gets anywhere. If you find that your set is obstinate and persists in oscillating, or is "unstable" and difficult to control, there is something wrong with it. Correct adjustment "of the grid leak will work wonders. There is a best filament bril-' liancy, too, and too dull a filament will make the commencement of oscillation very abrupt. • Some valves oscillate more easily than others, and the tickler coil should be changed if necessary. Too. many turns in this coil will cause persistent oscillation.

Sometimes a set will oscillate spitefully under the best treatment, and the trouble may be due to the B battery being run down, and of unduly high resistance. This can ho cured by replacing the battery, or prevented'by shunting the battery with a suitable condenser of large capacity—anything from .005 to 1 microfarad, and the..bigger the better. Connect one terminal of the condenser to ,the negative end of the battery and the 'other to that positive terminal of the battery to which the plate of the detector valve is conneced;. Not only; is this a remedy for the trouble referred to —it is good practice at any time, and kills' the small noises often caused by defects in the battery. Use' a good, sound condenser for this purpose. • , ' r

If 'all else fails, close down. Call in an expert—the man next door may be able to,help. You will not have to go far. If you cannot hear well, your set is sick, or you need some help. No wireless man should be ;afraid to send ,out au "SOS"—so long-as he doesn't do it with, his set: The radio fraternity is anxious to Kelp him. . . '