RADIO AND ITS RECEIVERS

Sun (Auckland), Volume 1, Issue 35, 4 May 1927, Page 10

RADIO AND ITS RECEIVERS

FROM TRANSMITTER TO RECEIVER

Should a note on the piano or other musical intsrument be sounded, that note produces a certain effect on one’s ears. This note is made up of vibrations at audible frequencies. In other words, in general, it may be said to be rpade up of a fundamental tone and several “overtones,” which are really harmonics of the fundamental frequency. Sound frequencies are designated as low frequencies, or audio frequencies. It is the composite nature of the note of a musical instrument that not only gives the note quality and character, but also distinguishes it from the same note on other musical instruments. The same applies to the human voice, as it is the relative magnitudes of the harmonics and overtones which give character and quality to a particular voice. This serves as an introduction tp our subject. When any programme is broadcast from a given station studio, the sound waves first impinge on what is called a microphone. Such a device is used so that the sound.energy can be transformed into electric energy. This electric energy is in turn amplified by a. special speech or voice amplifier. The output from this latter instrument is then impressed on what is known as the modulator, this in turn impressing these currents upon the radio wave which is to carry them through space. This wave is usually known as the “carrier-wave.” Such a carrier wave has a frequency of about 540,000 to 1,500,000 cycles, or complete vibrations, per second. In conseqLience these are known as “high-frequencies,” or “radio-frequencies.” These frequencies are inaudible, as the normal ear responds only to those of the order of about 16 to 16,000 cycles per second. Why this high-frequency carrier-wave is used is because it has been found to be more capable of being sent through space than other electric waves of lower frequencies. In order to produce the carrier-wave what is called an electric oscillator is used for generation purposes. The aerial is used in order to radiate these carrier-waves. Even if no -sound is being impressed on the microphone the carrier-wave continues to go out into space. However, it does not actuate a receiving set in an audible manner. As soon as the microphone is spoken into, however, a properly tuned receiving set will give a reproduction of the sound impressed at the transmitting station. Now the signals picked up by the receiving set are very feeble and therefore the first thing usually done is to amplify these weak signals, by passing them through a high-fre-quency amplifier. This in turn passes the increased energy on to the detector valve. This reverses or undoes whtit the modulator did at the transmitting station. From such detector the electric currents may pass into one or more pair of headphones. If a loudspeaker is being used they will be passed into a low-frequency amplifier first, so that the impulses give sufficient volume for operation. In closing, it may be remarked that such a combination of transfers leaves the chance of distortion creeping in should some small balance be upset between transmitter and receiver. Nevertheless it is possible by using good apparatus to secure perfectly excellent reproduction. RADIO LICENCES According to the report issued a few days ago in Wellington, it is stated that the total number of licences exceed those of last year. Under the circumstances this is probably better than the most sanguine hoped for. It certainly speaks well for the ensuing season, which really commences in earnest this month. In going through the totals they are certainly illuminating, not so much the difference between the four districts, as the percentage of dealers to listeners. “Raytheon” makes this as follows:

It would seem the larger number of dealer licences taken out in Wellington are in anticipation of the new station being erected there, and which according to latest reports will be “on the air” in July. Nevertheless, the number seems well out of proportion to the listeners-in. Even Auckland and Christchurch, with one dealer to every twenty-two receiving licences seems to be overdoing it. Certainly it means revenue to both the Government and the broadcasting company, mainly the latter, but it may quite easily be noted that such a percentage does not look too healthy for the dealer who serves. It would appear in the main that the trouble rests in the classification of the licence and it would certainly seem that some kind of revision should be made. For the receiving licencee such a move would probably mean better service from his dealer. CORRESPONDENTS’ QUERIES G. Ruatoria, E.C.—Letter to you. H. Epsom —Many thanks, although your list of questions is rather large. The questions are: (1) Which mast should be higher, why? I notice in some cases the mast nearer the lead-in is not used, but the aerial comes at an angle from the distant mast. —Answer: For preference the one nearest the house, in order to keep effective height ground equal. It is doubtful if much is gained, however. Such an aerial as you mention is the “straight-away” type, and has probably been substituted for an inverted “L” or “T” type. (2) Will publish information as soon as available. (3) Will the new Wellington station be heard in Auckland on a crystal set? Would a carborundum detector with stabiliser bring in 2YA? Answer: “Raytheon” understands IYA has been heard in Wellington on a crystal set, so that it would appear quite probable that the new 2YA will be received on some crystal sets here. Whether the detector you mention will do this will be a matter of trial. It would not receive the present 2YA. (4) Refers to claims of crystal users receiving distant stations, including some in Australia, and asks how it is done. Is the secret in using the very best headphones? Answer: Undoubtedly genuine reception has been obtained, and will continue. In the majority of cases there is no radical departure from the usual crystal circuit. Headphones, of course, are a factor, and ‘Raytheon” would recommend the following for success on a crystal set: Sensitive headphones (4,000 ohms or more) of the best quality, the best aerial and ground it is possible to get, good quality sensitive crystal, low-loss inductance winding, and 90 per cent, patience. (5) Would raising the aerial from 25ft. to 35ft. bring in the 50-watt local stations on a crystal set in this city? Answer: Certainly to be recommended, the higher the better, especially for crystal work, and up to 125 ft. long. Location has much to do with this. Cases are known where these stations have been heard clearly several miles

away, yet on the other hand others much nearer fail to secure reception from them. Location, again, is a factor. (6) Percentages are not available. The increase would be fairly expensive, but will doubtless be done later. (7) If the owner of a set visits a friend and tries his set, is he liable to a penalty? Must a licence be taken out before an enthusiast is sure he is within range with his crystal set? Answer: The Act is quite clear. Radio apparatus must not be erected or used without first procuring a licence. Likewise the set must not be transferred to other premises unless the authorities are notified and licence endorsed accordingly. (8) Is any advantage obtained by fixing a hollow metal ball on the aerial? Answer: The ball itself is the aerial. It is usually used where space is limited. (9) Can Australian stations be received in Auckland on a one-valve set, with any regularity? Answer: Yes, subject to atmospheric conditions, and location.

Receiving Dealer PercentLicences. Licences, age. Auckland ». .. 8,860 405 4.57 Christchurch . 4,410 195 4.43 Dunedin .. 1,584 109 6.88 Wellington .. 3,346 478 14.29 Totals .. .. 18,200 1,187 6.52