RADIO AND ITS RECEIVERS

Sun (Auckland), Volume I, Issue 131, 24 August 1927, Page 14

RADIO AND ITS RECEIVERS

Conducted for THE SUN by

C. M. Taylor, B.Sc., A.M.I.R.E.

UNCLES AND AUNTS The Broadcasting Company realises that in the modern home much consideration is given to the younger members of the family and in catering for the children it is doing much to boom radio in New Zealand. In this respect we are to have a regular daily service or children’s hour from all stations. Another very wise step is starting at 6 o’clock. Many children are in bed at 7 o’clock and much of the company’s efforts in this respect -would be wasted if the hour were too late. While on this subject the writer would like to see some slight serious touch introduced such as simple little stories about the tilings that really matter to us. For example, little stories about our flag, little bits about the history of our islands, the fairy tales of other countries and so on; but not too much nor too often. Stunts and novelties can be organised. There are many ways of entertaining children other than by the inane laughter and pointless remarks which bore the modern child to sobs. As lan Hay says, if you can interest a child you can do anything with him. THE SHORT WAVES

Novelty is very much the spice of radio. New stations are eagerly sought by the enthusiast. To the average set-owner this desire is limited to an occasional American station and possibly an occasional transmission from the Far East. A new field, not really new, but a field on which interest has recently centred is that among the short waves whose far-reaching properties are being used more and more. With the proposed short-wave station in England, and the already existing Dutch and American stations, interest is being stimulated in this direction. With the short-wave receiver a detector valve followed by one or two stages of low frequency amplification is used. While we have various types of broadcast receivers practically all employing one or more stages of high frequency amplification, the short-wave receiver uses the ordinary three-coil regenerative circuit, the main variations being in the method of control of regeneration. The outlay of a three-valve short-wave set is not very great, and if we can do without the two stages of audio amplification the cost becomes very light. A diagram of a successful short wave set is given below, and if the output from this set is taken to the audio amplifier of the family receiver two sets are available at a small cost. The parts needed are three coils, the aerial coil LI of 4-5 turhs. the grid coil L2 of 9 turns spaced about an inch from the aerial coil, and a regen-

eration or tickler coil L 3 of 5-6 turns wound as close as possible to the grid a 3-incli low-loss former or selfcoil. These coils can be wound-spaced on supporting on the Lorc-.uz basketweave principle. Wire 20-22 gauge should be used, and may be cotton, silk, enamel covered or best of all, bare. The cotton-covered wire should be doped, as our Auckland climate is so moist that leakages soon occur due to the nature of this covering. A good condenser of low-loss design, is the Ormond, Wavemaster or General Radio. A vernier dial is more than a convenience; it is a necessity. The conventional grid leak of about four megolums and its condenser, valve socket a variable high resistance, a radio frequency choke coil, and a .5 M.F. fixed condenser are all that is required. Aerial and earth terminals panel, three lengths, of good quality flex, and an old valve of the type used in the detector valve of the broadcast receiver make up the complete list. The glass is removed from the old valve and the three pieces of flex soldered to the plate and filament legs, the grid leg not being connected to anything. The socket is then filled up with Chatterton’s compound or sealing wax. The set is wired up as shown on the diagram. One piece of flex from one filament leg of the socket is connected to A. In this respect this filament leg preferably connects to the X filament lead in the broadcast receiver; but, failing a voltmeter test to show which is the filament spring in the detector valVe-socket it is a simple matter to try afterwards which gives the better results. The piece of flax from the other filament leg of the socket goes to B. The remaining piece of flex is connected to C. The radio frequency choke can be made very simply from an old pair of headphones, each coil of which if removed from its core of iron and unwound to about half makes a satisfactory choke. The wiring and layout follows usual practice in low-loss sets —leads as short as possible and grid and plate leads not bunched together. The set is coupled to the broadcast receiver by plugging the old valvesocket into the detector valve-socket of the receiver. The detector valve may quite well be used as the valve in the short-wave part. The radio frequency valves are turned out if such control exists or else removed from their sockets, and the listener is ready to explore a region hitherto unknown to him. All tuning is done on the short-wave set. PROGRAMMES The quality of the programmes is still criticised by many listeners. Be that as it may, there is no doubt that on Friday night IYA broadcast the best programme so far transmitted from that station. Among the new apparatus to hand are three high-wave Mullard valves, the 6-volt PMSB, the 4-volt PM3A, and the 2-volt PMI A. These valves have a very high amplification factor, about 40, and are specially designed for re-sistance-capacity amplification in lowfrequency stages, and for high-fre-quency amplification in circuits of the tuned-plate types. They have the usual P.M. characteristics of robust construction and high emission, with small filament consumption. THE SUN, remembering the old DFA4 of similar design, and a wonderful detector, tried the new series in this respect with very good results. A neat crystal set, the Lambert, was sent to THE SUN by Messrs. Abel Smeeton. It gave quite the best volume heard from a crystal and the catswhisker control is the first one seen to give a really variable pressure control. The crystal appears to be a form of galena, and the pressure is controlled by a small sliding weight. This variable pressure has a great deal to do with the sensitivity, as most crystal users know a difference in pressure on the same sensitive spot makes all the difference between good and ordinary reception. Reports in Auckland have

already been received of reception of Wellington while Auckland was on the air, no mean feat in both sensitivity and selectivity for a crystal set. RECEPTION OF NEW ZEALAND IN AUSTRALIA When New Zealand stations were flx-st established, the engineer who had charge of the installations did not come over with the machinery, says an Australian writer. Local engineers set about to complete the job, and, to an extent, did wonderfully well. Lately, enthusiasts in Australia have been congratulating themselves on the way they “bring in” New Zealand. Finer results, of late, are due to the completion of the “Enzed” installation. Managing director McLardy, of 2BL, received instructions from the Post-master-General’s Department to drop the wave-length of 2BL to 349 metres. This was carried out, so that 2BL is now further away from the wavelength of IXA. This will answer the many inquiries as to why New Zealand is being received so well in Australia. The change, too, accounts for the splendid loud speaker reception from the land of quakes and shudderg. The “Radio F,ecord,” the official organ of the Broadcasting Company, has certainly come to stay in local radio circles. The Wanganui Association considers it fills a long-felt need and there is no doubt that it is the best all-round radio journal published in New Zealand to-day.