WIRELESS NOTES

New Zealand Times, Volume LI, Issue 12022, 27 December 1924, Page 15

WIRELESS NOTES

By RADIO.

In answer to numerous inquiries *©- ©oived. a design of a simple single valve crystal detector is shown. The circuit suggested is one that is easy to make, and after trying it out one could go a step further and make a reflex circuit. The letters are as follow: 14, loading inductance: L2, variable inductance; £>, crystal detector; C, variable condenser .0005 mp: AT, audio frequency transformer; y, 201 A valve; It, 6 ohm rheostat; Cl, 'phone condenser; A, 6-volt aociimulator; B, 901 volt dry cells; T, telephones. The B battery will depend upon the type of valve used, and will vary from 30 to 90 volts. The A battery wdll al6p vary in the same way—4 to 6 volts—either dry cells or accumulator. If a dull emitter valve is used, then dry cells will be all that is required. The audio transformer (AT) should b© either 4 to 1 5 to 1 ratio, and the tuning condenser (C) about .0005 m.f. will be quite large enough. SUPERS NO AID TO OTHER SETS There is little truth jin the popular belief that operation of a superheterodyne improves the reception of other receivers in the neighbourhood. It is often said that the receiving range of other set© is increased when a "super" is operated in the vicinity. This belief is only natural, as the "super" is looked upon as a powerful and sensitive outfit. But, as a matter of cold fact, a one tube regenerativo set is capable of decidedly more improving effect than the usual eight tube superheterodyne. In order that o. receiving set may increase the volume or apparent range of other nearby sets, it is necessary, first of all, that the receiver amplify the initial received frequency, and, secondly, that this amplified energy be coupled in some way to th© antenna, system, and | thus increase the energy in the,antenna end cause greater radiation than would be the case without the transference of I amplified energy at the same frequency. ' A - plain regenerative set does both of these things, as the initial energy is amplified and the amplified energy is coupled, while still at the earn© frequency, to the antenna circuit, so the energy in the antenna is reinforced. The receiver' need ' not be oscillating to accomplish this, though the ©fleet will be greater the nearer tho receiver is operated to the (point of maximum regeneration. ORIGINAL' FREQUENCY- NOT AMPLIFIED But with a superheterodyne the original frequency is seldom amplified. The only radio frequency energy present of any appreciable value is that at the frequency of the oscillator and that at the intermediate frequency. The oscillator fiequency is not in tune with the receiver frequency, and in any Cose is not modulated; so even though energy be radiated at the- oscillator frequency it will be of no advantage to nearby receivers. The amplified intermediate frequency is not in resonance with any of the broadoast receivers, nor even in resonance with the antenna of the super. Besides, the amplified intermediate frequency is almost completely isolated from the antenna circuit, so even if energy at the intermediate frequency was radiated it would have a negligible effect not only as it is completely out of resonance with the superis antenna and neighbouring receivers, but also because the value of radiated energy would be absurdly small. , *

. Therefore, unless regeneration is employed in the tuning section of the super,

the radiation will bs no greater than would be the case were all the tubes removed. And even if regeneration were used radiation would not be in excess »f any regenerative one tube set, and possibly even less so because of tho smaller antenna generally employed with the super. Eememb3ring that the sensitivity and amplification of a super comes after the soeond or third tube, and even then at a different frequency from that of cither the super’s, antenna or nearby broadcast receivers, it can be seen that this belief is the bunk.” OUR DEBT TO RADIO I wonder how many lives hflvo bean saved by wireless during the short life of the magic science, asks “Popular Wireless”? In the early days I’ remember seeing a table giving the exact number, with the names of different ships, Republic, Titanic, Volturno, etc. (There were over 500 saved on the last alone.) Ten years ago the total became unmanageable, and had to be estimated; and the full tale of wireless life-saving in war time Can never be guessed except by those who saw behind the scenes. BROADCASTING "Now that electrio waves are so easy to produce, and so absurdly easy to detect, it is amazing to think how long it took to discover them, and how many times they hinted at their existence before they Were properly recognised and appreciated."—Sir Oliver Lodge, F. 8.5., D.Bc., LL.D. “The thing that was wonderful yesterday is mediocre, to-day and stale to-mor-row. There is neither satisfaction, nor end to the labours of the broadcaster in his endeavours to give his listeners the best possible service which experience and imagination can supply."—Mr J. C. W. Keith, managing director, 8f.8.C. COLOUR BY RADIO Colour by wireless is tho interesting invention of Captain <J. A. Taylor, who is president of the Association for Developing Wireless in Australia. Hie machine takes advantage of irregular contact on metal plates, upon which the picture has been etched in acid. The contact can make or break wireless s*gnals, which thus reproduce the picture at the receiver, and bo bring us nearer to the dav when we shall see broadcasting, as well as hear it. A DON’T FOR AMATEURS Don’t leave your instruments Connected to your aerial during thunderstorms. The electrical changes collected by your aerial are apt to damage your receiving instruments. It is advisable, therefore, to disconnect your aerial down load from the “aerial" terminal of your receiver and • connect it direct to the earth lead. The receiving instruments are thus cut out of the circuit, and the aerial, being connected direct to garth, acts as a useful “lightning-conductor." An asrial-to-earth switch can be purchased for a few shillings. This enables you to "earth" your aerial at a moment’s notice without having to make any hasty connections; by throwing the handle of the switch from one side to the other, the receiving instruments are automatically excluded from the circuit and the aerial joined direct to earth , * < -