RADIO RECORD

Greymouth Evening Star, 27 September 1928, Page 7

RADIO RECORD

NOTES FOR LISTENERSJN

(By

“Reception”)

CRYSTAL SETS. SIMPLEST WIRELESS CIRCUIT. The crystal receiver employs the simplest of all wireless circuits. It is easy to build and simple to operate, and its upkeep costs are practically nil. It will give good headphone strength up to 20 or 30 miles away from a. high-powered broadcasting si a--lion providing that. a. good aerial is used. Its chief disadvantage as compared with the valve receiver may be summed up as follows: It will not successfully operate a. loud speaker, and it is rather difficult to tune out undesirable stations. Furthermore, most types of crystals require frequent adjustment which, in addition to the aforementioned interference rather tends to mar the enjoyment of the programme. Interference, however, may be greatly reduced by carefully following these instructions: Pay particular attention to .the aerial and earth as recommended. Bear in mind that both signal strength and interference increases in proportion to the height of the aerial. Decreasing the height will reduce interference to a greater extent than signal strength. Therefore city dwellers shguld keep their aerials as small as possible, consistent with comfortable reception. Before buliding a receiver, select a circuit employing both aerial and secondary coils tuned by variable condensers. These two coils should be kept as far apart as possible when interference is experienced. This will make the tuning sharper and interference from undesired stations will be reduced The crystal proper plays a very important part in the. reception of wireless signals. Briefly, it converts the feeble alternating currents into undirectional impulses, permitting these to have audible effect in the headphones. Crystals may be divided into two distinct classes. The first type, commonly known as “perikon” combinations, requires a second crystal to be in contact with it. The second class are those crystals requiring a metal contact. Crystals such as tellurium and zincite; zincite and copper pyrites; zincite and bornite come under the first class. The perikon combinations are not popular among broadcast listeners, so we will pass on to the second type without further mention of them. In the second class there are galena, iron pyrites carborundum, molybdenite and illicon. Both sillicon 'and carborundum require a steel contact; galena will work equally well with gold, silver, brass or copper contacts. Carborundum is the most reliable .crystal, but it requires a streevolt battery and a potentiometer for successful operation. Galena, whether synthetic or natural, is one of the most popular crystals. It is extremely sensitive, but it requires a very light contact with the cat’s whisker, and therefore is very liable to be thrown out of adjustment. However, the synthetic types of balena do not suffer from this effect to the same extent as do the natural types. Crystals should on no account be handled with the fingers. If they become insensitive they may be cleaned by immersing them in alcohol for about ten minuts, and the allowing them to dry. Headphones used in conjunction with a crystal set should be of the high resistance type (3,000 or 4,000 ohms), and when two or more pairs are used they should be joined in parallel. In order to join two or more pairs in parallel, take one phone tip from each pair of phones and securely fix them to one of the phono terminals of the receiver] The remaining tips are connected to the other phone terminal. Finally, when using several pairs of headphones make quite sure that they arc all of the sanie resistance, otherwise the lower resistance telephones will have more than their share of current.

EFFICIENT RECEIVING SET.

231 STATIONS VERIFIED

Most people in New Zealand have the idea that with the multiplicity of broadcasting stations in America it must be very difficult for American listeners to listen-in comfortably to any particular station, and that there must be a lot of “blanketing” by local stations. In the course of an interesting letter,' Mr. Philip C. Kenton, of Long Beach, California, makes it clear that this is not the case. He forwards a copy of his log containing 231 stations which he has heard, and of which he has had verification. The list is a remarkable one and includes stations in every State in America, Canada, Mexico, four English stations, Scotland, South America, Wales, Japan, Germany, France, and IY r A, 2YA and 4YA New Zealand. All stations were on the broadcast band as Mr. Kenjon does not possess a short wave receiver.

BRITISH BROADCASTING. The British Broadcasting Corporation’s report for 1927 shows a total income for the year of £901,00, of which £800,900 was received for licenses. The sum of £490,000 was spent on programmes. There were 68,000 hours of transmission during tho year with only about twenty hours of breakdown. Music occupied twothirds of the programme. An increased interest in educational broadcasting is shown, the report says. Four thousand schools were known to listen to London and Daventry alone—double the unmber of the previous year’ —and about 1500 adult educational bodies cooperated in the distribution of the sessional talks programme. The total number of listeners increased by 217,000 during the year to 2,395,174. The five-minute charitable appeals on Sunday were known to have realised £40,000. though the actual sum was! considerably larger.

NOT ALL COMPLIMENTARY. .Even in Australia the programmes do liot please everybody. When listeners were privileged to hear Dame Nellie Melba as “Mimi” in “La. Boheme,” an invitation was extended by the. New South. Wales Broadcasting Company to those who wished to express thenappreciation by letter, to write to the sludios, and their messages would be conveyed to the. Dame personally. From all parts of the Commonwealth tellers came pouring in, in congratulation of (be brilliant performance. The opinion of nearly 2000 people could be summed up in one word, “Wonderful.” There was one exception. A “round robin” from live people declaimed with soured unction. “We, the undersigned, consider Melba’s programme rotten!”

static-reducing device. IS THIS THE REAL THING? We have heard so often about static eliminating and reducing devices, all of which have been valueless, that we are inclined to be a little .sceptical when any fresh one is announced. However, the following from Washinglon sounds good. The static, reducing device, designed by William -I. Scott. veteran of tile naval reserve, and onetime repairer of band instruments, is functioning successfully at Radio Central of the Navy. “This instrument has been of great assistance on the long distance low-frequency circuits, such as Balboa, San Francisco,* and San Diego, making reception through static possible when normally signals would have been unreadable,” says the official bulletin of the communications division. Navy engineers describe the operation of the device as follows: ‘'‘The clariphone operates as a. sound filter. It consists essentially of a loud-speaking unit, several sections of small brass tubing and a microphone, all of which are enclosed in a padded, sound-proof box. tubes are so arranged and of such dimensions that they will permit the passage of sound waves or tones of a definite frequency only. Th© present installation is adjusted to pass a tone of approximately 2,000 cycles, rejecting all others. The radio receiver is tuned to produce a signal beat, note of 2,000 cycles, which operates the loud speaker unit of the clariphone. This unit operates in a small air chamber, converting the electrical energy into sound waves. The sound waves are conducted through a system’ of air chambers and tubes, each, section of which assists in the filtering out of interfering noises. The signal is finally picked up by a microphone which converts the sound waves back into electrical energy and operates a. pair of head-phones.” A FEW TIPS. Porcelain Insulators for Aerial. — Glazed porcelain insulators and highgrade types of moulded composition insulators are best suited for aerial insulation.. Spreaders should not carry parallel insulators on each wire; this reduces the insulation instead of improving it. The insulators should be placed in series, and strung at each end of the spreader rope. Phone Cords.—lt is often found that phone cords fray where they enter the terminal tags. This can be prevented bv pushing two lengths of cycle-valve rubber, each about lin. long, on to each terminal tag. Force the rubber on to the broad part of the tag, and roll a small portion of tlTe rubber nearest to the cord back on itself. Push the rubber still farther on, and then the rolled-back portion can be unrolled on to the cord.

Hand Capacity Effects. —A metal shield will reduce hand capacity effect to a minimum in a set. It has been found that in a well-constructed, carefully designed set capacity effects, are absent.

Use of By-pass Condenser—lt is a good plan to use such a. condenser, although the set will operate without. It usually improves the control of the regeneration. Rango. of Crystal Receiver.—The consistent range of a crystal receiver is from ten to twenty-five miles. However, under freak conditions, receivers of this type have been known to pick up signals of stations more than 100 miles away.

Loose Valve Contact.—-When the valve does not lit properly in its socket a toothprick or a match whittled down to form a wedge can be placed between the socket and the valve to hold it tightly in place. Crystal Sensitivity.—A sensitive spot, on a crystal soon loses its sensitiveness. When one spot is exhausted find another, until the crystal is finished. Keep your lingers off the crystals.' Shore Wave Aerials.--It is common knowledge amongst many persons that on (.ho short wave lengths correspondingly short aerial should be used. This is not so, as experiments have proved. It. was found that for five-metre reception the longest aerial possible, but no earth connection, proved to be the best possible method of pick-up. For reception on. wave lengths from fifteen metres up to 100 metres an aerial with an overall length of 250 ft. is advisable. This will give a greater pick-up of R.F. currents.

Utilising the Old Valve.—A receiving or transmitting valve that will not oscillate any more can be made to serve as a rectifier valve as long as the plate or grid is not shorted to the filament. The socket, springs connecting to the grid and plate of the valve should be wired together, so that the valve will carry more current.

Testing a. Valve—Tho best test for a new valve is to. put in a regenerative receiving set or oscillator, and determine whether or not it will oscillate. This is true, because a valve that will oscillate will also detect and amplify (the two other functions of a valve). This is the test often used by manufacturers and dealers. A valve that will not oscillate is practically worthless for any use but rectifying. It is a very good practice to use rubber-covered wire in connecting up storage batteries, due to the fact that it is not affected by the acid fumes and spray caused by charging. Ordinary insulation in time soon burns off, leaving the wires bare and sometimes causing the short circuit which will ruin, the battery or charger, and in some cases may even cause fire. Corrosion may also be eliminated from battery terminals and adjacent leads by a liberal coating of vaseline on both before the connection is made.