RADIO RECORD

Greymouth Evening Star, 1 August 1929, Page 7

RADIO RECORD

NOTES FOR LISTENERS-IN

(By

“Reception”)

• HUM IN CRYSTAL SETS HOW TO CURE IT Crystal receivers seldom give trouble from tm interference point of view. Nevertheless, some crystal do suffer now and again from a most annoying hum in the phones of their instruments. Such a, type of disturbance is, of course, generally due to the proximity of a generating station, dr to some portion of the elqctricJighting circuit of the house which may happen io be running closely parallel to a part of the aerial circuit of the set. Also, the trouble may be due to some peculiarity of the electric mains running outside the house, and perhaps in the neighbourhood of the earth plate of the receiver. Naturally, the best method of eradicating such a trouble is to ferret out its cause in a logical manner, and, having found' it, to remove it. In many cases, however, this line of procedure is unfortunately not practicable. However, quite an efficient method of dealing with the crys-tal-set. hum trouble consists in placing a moistened finger tip on the earth terminal of the receiver. In the large majority of instances this will result in the disappearance of the annoying hum, the latter disturbance, of course, instantly returning after the finger-tip lias been removed from the terminal. In such cases, however, the elimination of the hum may be made more or less permanent by attaching a sft. or Gft. length of bars wire to the earth terminal of the set, and by allowing it to dangle loosely on. the floor. Alternatively, the free end of the latter, wire may be connected to a metal plate laid upon the floor, or again the wire.may be attached to some extensive metal object in the room, such as, for example, a kitchen range, a steel or brass fender, a gilt-framed picture of large size, and so forth.

This extra loose earth connection, acting as it does owing to the setting lip of a. means of capacity leakage, has the effect of allowing the oscillations responsible for the troublesome hum to leak, away to earth.

WINDOW WITH A VOICE Though we have long looked upon the shop window as-a “silent salesman,” it seems that our views in this respect must be modified. In one of London’s leading stores, window 7 space has been devoted to demonstrations of cleaning pots and pans by means of a new polish, and in order that the demonstrator may “get the story across” a microphone has been fitted on the inside of the w'indow, with a Joud speaker on the outside. By means of these two instruments the demonstration of pan polishing is accompanied by a series of vocal explanations, thus holding the attention of both ear and eye of the audience.

A LITTLE FLASH What would you say if, on inserting one of the H.T. battery plugs’ (and when (he set was in a dark corner of the room) a little flash appeared on contact? And this with the filament switch still in the “not yet’ position? And what would you say if, on disconnecting all batteries and plunging your hand into the wiring to locate the fault, you received a healthy, sharp coup de’electricite? I mean, of course, what would you say by way of explanation, and not as an ejaculation! The whole thing is one which has puzzled many people, for apart from •the fact that no lI.T, current should be able to How when the L.T. supply is “dis,” liqw can a shock make its presence unpleasant if all batteries are disconnected? The H.T. condenser is the culprit, as you will find out if you put your fingers across each pair of leads hi turn, in order to get a second shock! The. reason is that, even though the filaments are out of circuit, the full H.T. potential is applied to this condenser when (he wander plugs are inserted, and it absorbs current up to its full charge value. Hence the spark. A good condenser will hold its charge for a long while —often many hours —and if its terminals are touched while there is still a portion of the charge remaining a. severe shpck will be felt. This is, in fact, a. test of the efficiency of the condenser, which should bo able to absorb a fair amount of H.T. current, to hold its charge for a long while, and thus to act as a “smoother-out” of high-tension variations. It only remains, to add that, if you have any doubt of the chargeholding and shock-producing powers of a condenser, test it for yourself! THE SYDNEY SCHEDULE

■The following schedule laid down for 2FC and 2BL are of interest to New Zealand listeners. The times given are New Zealand standard time: 2FC, Sydney—Mondays to Saturdays —Early evening, 7.15 to 9.25: Children, dinner orchestra (8.15), sporting news (9), and organ recital (9.15), Evening concert—9.3o to 1 u.m.: 9.30, concert (presentation; 11.45, announcements; 11.50 pm., dance music. For Sundays—--7.30 pm., instrumental music from studio; S.lO, address suitable to the day by a clergyman, professor or prominent man; 8.30. orchestral music; 9, grand concert programme; 11.30, meditation music; close at midnight. 2BL, Sydney (us from July).— On Saturday afternoons, sporting resume, 6.30 to 6.45. Daily: 7.45 p.m., dinner orchestra; 8.15 to 8.34: Mondays—Boy Scouts; Tuesdays—Girl Guides; Wednesdays—bigger boys; Thursdays — bigger girls; Fridays —athletics; Saturdays—tales of Adventure. Daily: 8.35 —markets, news. 9: Dinner Quartette. 9.30: Concert programme, closing at midnight. On Saturdays dance music will be provided from 10 p.m. to 2 a.m. For Sundays —6 to 7.30 p.m., organ and band recitals, and studio programme;. ' 7.30: For hospital children; 8.10: . Studio music; 8.30: Church, service; 10 to 11.30: -Studio concert, ‘band jecital; relays from Melbourne, etc.

INTERFERENCE ATTACK IN G ST ATI CIncreasing the power of the trans.nutting station and increasing the ‘.selectivity of the receiver are unquestionably feasible methods of reducing static interference. Suppose one is experiencing static while listening to a broadcasting station, the only way to reduce this static is by bringing the selectivity of the receiver near to the ideal. Static is considered to be a mixture of disturbances of an identical nature to those received from the transmitter lienee that portion on the received frequency will inevitably be received. From the foregoing one will conclude that static cannot be eliminated, which is quite true. However, the previous statement suggests new methods of attack. Why must one receive on the conventional type of aerial? Why not devise a. very directional type, which will reduce the area from which the atmospherics can be received, and so will increase the signal static ratio? The loop aerial has very directional properties. Again, on© must suppose that certain wave lengths are rworse for atmospherics than others. This may be another way out of the dillijeulty. There are two kinds of atmospherics—static and strays. Static is generally known to take in any electrical disturbance, whereas it is the electric charges that are carried to the receiving aerial by particles such as dust, snow, or moisture in the air. When these strike the aerial they give up their electrical charges. When connected to the receiver and then through an inductance or direct to earth, they ordinarily pass silently to earth. However, when there is a series condenser, these charges mount up until the charge is so great that it sparks across the condenser, and a loud noise is heard in tile receiver.

ELECTRICAL INTERFERENCE

Bulb and electrolytic battery chargers are now in many households. The vibrating reed type has long since been displaced, though a few still exist. The reed type battery .charged is a public nuisance. The irregular clicking sound emitted by this rectifier corapletel prevents satisfactory reception of evert the local station when using a valve receiver. Household electrical appliances are also a source of very troublesome electrical interference. The electric iron emits a buzzing sound on wave lengths below ithirty and forty metres, but this is not usually troublesome. The electrical cleaner does not usually receive mechanical attention, and soon the contacts of the brushes become ■worn, and bud contact is made in the machine. The result is that the sparkjug of the contact causes interference in the form of a cracking noise, which, though travelling only a comparatively small distance, is capable of spoiling reception in neighbouring receivers of a number of blocks away. When using aerial adapters to the electric light mains the trouble from this source is usually more pronounced, the damped radio frequency waves generated in the machines travelling buck through the lighting system and via the adapter to the receiver. Leaky power lines also cause extensive interference. In the United States a number of special cars are fitted with direction finders and suitable equipment. These cars are for the purpose of tracing down leaky power lines and faulty high-pow-er transformers. If you are unfortunate enough to be situated near a power station, it is your bad luck. It would be practically impossible to eliminate interference completely on such an extensive scale. Though the percentage efficiency of br;th the electrolytic and short path bulb rectifiers is not great, they can be used when a receiver is in operation thus showing that they , arc not a source of interfering radio waves.

JOTTINGS

Listeners do not have to pay any licence fee in the United States. Shortly after the inception of broadcasting there some one started the idea of selling the time of the stations to advertisers. One can buy rime from some of the central broadcasting stations in America in the same way as one buys newspaper space. Ai. tire beginning however, this was a failure, because the charge was too cheap, and it only became a success when an enormous value was put on such advertising. The broadcasting companies in the United States which are now selling time in this manner are getting rich and powerful, are spreading their net-work all over, the country, and large commercial undertakings uro competing for permission to “sponsor” the programmes which the advertising' companies are putting on tile air. The sponsored programmes are of a very high musical standard and only indirectly used for advertising purposes.

Galena is the crystal most recommended for Jong distance crystal set reception. Instead of the usual wire cat’s whisker, try a small pointed piece of graphite from a “B” grade lead pencil. Bind if. to the cat’s whisker with a lino wire and make contact with the •crystal with the pointed graphite. This combination is very sensitive and its adjustment very critical. The contact with the crystal should be very light. Platinum also makes a good cat’s whisker, owing tp.. its non-oxidis-ing qualities. As it is expensive a small portion only need be used, attached to the ordinary cat’s whisker. A radio receiving set, only 12 inches long, eight inches high and two and three-quarter inches thick, nicknamed the “Pancake receiver,” has been developed for use on airplanes, It is intended to be installed in the side of a cockpit and is so designed that it will give a minimum of interference 'with the pilot or assistant. Its control knobs and dials are constructed and carefully bevelled to avoid catching on clothing or equipment of the aviator, in the event that he wants to leap from his ’plane with a parachute. Yet they are so designed that they can be operated easily even when the pilot is wearing gloves or mittens. To Professor Davies of the McGill University, at present attached to thei Byrd Antarctic expedition'as physicist, 1

every two weeks is sent by his university a- radio message to Little America, giving a brief account of the latest achievements of other physicists and the latest queries in natural science. Two of the. radio messages sent recently read as follow 7 : “As far as possible report through Commander Byrd, southern lights of aurorae, so that we can ascertain whether they coincide with the northern lights of Europe and America. Rutherford and Aston have discovered the origin of actinium, an isotope of uranium.” The second radio message read: “Please pay particular attention to the structure and density of the old glacier ice. Collect, if possible for analysis, some of the ancient air enclosed for thousands of years in the glaciers. The air from Greenland icebergs has been found similar to atmosphere nowbreathed, though it must have‘blown over the earth in the time of the very ancient Egyptian kings.” The Pan-American Airways Inc.', whose air service extends from New York to Buenos Ayres, has 51 airplanes now in service and all are equipped with 100-watt radio telephone and telegraph transmitters. The ground stations of which there are 72 either erected. or being erected, are 200-watt installations, and are capable of communicating over distances up to 1000 miles. From the minute a ’plane takes off until the time its wheels touch the ground, it is in the hands of the radio division of the Airways Company. The location of each ship is known at all times. Operators at the ground stations maintaining communication with an airplane, keep constant check of its bearing, and should the pilot drift off the course more than two and ahalf miles either side of the direct line, he is notified of his position, and advised in which direction to steer, in order to gain his direct route. In the cities with their variety of entertainment the radio receiving set is only one of many ways of getting enjoyment and recreation. Country listeners, however, in many cases have to rely solely on their wireless receiver for their news, entertainment iand information. A representative of the Broadcasting Company who recently passed through the interior, had the importance of broadcasting to the country listeners impressed upon him. .Among the expressions heard from individual listeners were, “1 don’t think you can possibly realise all that our set has meant to us.” “Radio has given up a new and wider interest in life.” “We should feel utterly lost without our receiving set.” “The very last thing w-e should think of parting with.” In- a ope-room shepherd’s shack the occupier said, “To right! I'll tell the world. I tune in before I put the billy cn, and let ‘er go till 1 turn in. and its great.”