THE RADIO WORLD

Southland Times, Issue 19658, 7 October 1922, Page 9 (Supplement)

THE RADIO WORLD

(By “Valve”) Tfi? weather that has been coming of late will initiate radio enthusiasts yho have installed receiving sets, into the troubles of serious interruption by the atmospheric conditions. Static electricity is the cause, and it. produces crackling and spluttering at the phone. This is sometimes hard to distinguish by the novice, who might easily imagine that he is getting an awful confusion of a real signal. Static electricity is always present in the atmosphere, but it is much worse at some times than at others. Coldness means a diminution in static, and it is in the warm months of spring and summer that it becomes the greatest nuisance, sometimes being so powerful in its interruptions that broadcasting stations have to suspend operations, and occasionally interfering so much with radio signa's that even the great high power arc stations are hindered in their commercial work. <♦><•>*■ A canoe in Australia went out-on a cruise recently equipped with a radio receiving and transmitting set. Power was given by four dry cells, and the antenna was a wire which trailed alongside in the water. The canoe, which went on a week’s cruise, contained, besides the radio set, a crew of two, who obtained a great deal of amusement in addition to the ordinary delights of a water-trip in good weather.

With a 100-foof, well-spread aerial, the length allowed by the Postmaster-General, it is possible to pick up the big Australian stations, and also to hear all the official stations in New Zealand. ■S’ BROADCASTING. CANTERBURY LEAGUE INTERESTED. . A lengthy report on wireless and broadcasting of radio messages was presented by Mr J. E. Strachan, headmaster of the Rangiora High School, at the last meeting of the executive of the Canterbury Progress League. Mr Strachan reviewed lhe development of wireless in New Zealand since 1899 and submitted a scheme for ,'he regulation of broadcasting. Tn a supplementary report, Mr Strachan stated: Since the foregoing report was prepared a draft of the new wireless regulations has appeared in the newspapers. On the whole these regulations will, I think, meet with the approval of all who are interested in the subject, and the Post master-Ge neral is to be congratulated upon his earnest, if somewhat belated, effort to remove the absurd restrictions of the past. A new interest has been added to life and up-to-date institutions and private individuals will no cioubt speedily avail themselves of the new privileges. As Christchurch is one of the lucky broadcasting centres, I presume that the Progress League will further justify its name and reputation by installing a broadcasting station for the dissemination of Press ne'ks, market reports, lectures, etc., for the benefit of its patrons. There are two respects in which I think the new regulations might be improved. (1) In giving to local wireless societies, which have the public interest at heart quite as much as the P. and T. Department, a considerable measure of control over local receiving and transmitting stations. (2) In giving amateurs of grade 1 an alternative wave length of say 1000 metres. Finally I think the League would do well to issue a warning to those contemplating the purchase of receiving apparatus. Receiving apparatus should be purchased only from reputable persons and firms and should be covered by adequate guarantees as to reliability, efficiency and suitability for use over a range of 120 to 400 metres. On the motion of Mr Aschman, it was decided to ask Mr Strachan to select a committee to keep in touch with broadcasting developments and the regulations governing the transmission of messages. 3> <•; TUNING COILS IN RECEIVING CIRCUITS There are several forms or arrangements of coils used in received circuits for tuning such circuits to the wave length of the sending station. When two circuits are in tune the natural period of electrical vibration of the two are the same. The two circuits are tuned to reasonance. The product of the inductance and capactity of the one circuit is equal to that of the second circuit. The tuning coil supplies inductance to the circuit, the amount depending on the number of turns on wire rather than on the length of wire in the coil. The simplest form of tuning coil consists of a single layer of wire wound around a cylinder and a rod and sliding contact so arranged that any number of turns desired may be used. This is known as a single slide tuning coil. It may be connected between the aerial and ground to tune the aerial ground circuit to that of the sending station. If two sliding contacts are used it is a double slide tuning coil. This second sliding contact permits the detector circuit to be tuned more accurately to the aerial ground circuit. The detector circuit is called the closed circuit and. the aerial ground circuit is called the open circuit. It will be seen that one winding or coil sen es for both circuits. If two coils are used, one for each circuit, so mounted that the distance between the two can be varied, tuning can be accomplished more accurately and there will be less interference; in other words the system will have greater selectivity. The loose coupler consists of two windings, a primary and a secondary, one of which will slide within the other. There is no electrical connection between the two and and energy is set up in the secondary winding (closed circuit) by induction from the primary vending (open circuit). The two windings are said to be*coupled electro magnetically. The coupling is close when the windings are near together and loose when the windings are drawn apart. The number of turns or inductance in each circuit can be varied either by sliding contact or by taps brought out to switch points. The coupling between two coils can be varied by rotating one coil within the other. The vano-coupler is of this form of construction. It can be mounted easily on the back of a panel and a knob and dial in front will permit easy and accurate adjustment of the degree of coupling. The variometer is contracted similar to the vario-coupler except that the two windings are connected together. When one winding is rotated the mutual inductance between. the two windings is changed and the effective inductance of the unit as a whole is changed- It has no sliding contacts nor switch points wherein there are opportunities for small energy losses due to poor contacts and it is therefore a very efficient- tuning unit to employ in a receiving circuit. When it is desired, to tune the open circuit to a wave length above that which can be secured with one tuning coil a second coil can be connected in series with the first. The second coil, which serves to add the required amount of inductance, is then called a loading coil. There are also tuning coils known as bank wound, honeycomb and duo-lateral wound. These coils are usually of fixed inductance

and their wave-length can be varied by using variable condensers connected to them in parallel. These coils have a number of advantages over the loose coupler. They are much more compact and there are no losses due to poor contacts. So-called “dead-end” losses are eliminated, these f>eing such as occur in portions of inductances, not switches in circuit where sliding contacts or switch points are used. Due to the form of winding the high frequency currents can pass through the windings with low resistance and therefore a maximum of energy reaches the detector. Coils of different inductance valves can quickly be inserted and the effestive wave range of the receiving set can be made to reach any practical values.