WIRELESS

Wanganui Chronicle, Volume LXXXI, Issue 19057, 9 July 1924, Page 10

WIRELESS

By

The Grid

High Frequency Amplification. 11 The Grid” has lately been conducting some experiments with high frequency amplification and reflex working. Although the latter method of utilising a valve is much used in other countries, it does not seem to have come into favour here, for what reason it is hard to say. In this article “The Grid” does not wish to touch on reflex working, but proposes to give the results of the pure high frequency experiments. The aerial upon which the tests were carried out is a poor one, being a single wire only sixty feet long and on an average eighteen feet high. The earth is also bad, being only a couple of feet of galvanised pipe buried upright in the ground. Owing to the situation it is difficult to erect < a good aerial or to obtain a good earth ( contact. In consequence the results : obtained are poor compared with those ( obtained on good aerials; nevertheless j the degree of amplification obtained < with different circuits can be just as j well determined as if a large aerial < were used. The low natural wave- j length of the aerial can be gauged by | the fact that the aerial‘coupling in- < ductance contains nineteen turns i (spider web type on a former as later j described), and in addition a loading i coil of sixteen turns is employed. The t secondary coil is also a spider web, hav- < ing an interval diameter of three and g a-half inches and wound with thirty t turns of 22 gauge d.c.c. This is i shunted by a .005 mfd. variable con- 1 denser, which, enables the coil to cover ( a range from about 150 metres to 360 metres. The reaction coil is wound ( on a similar former and contains thirty- ( one turns of 30 gauge d.c.c. The sec- s ondary coil is connected to the high t frequency valve just as to a detector, s except that no grid condenser is em- s ployed. The plate current to the high f frequency valve passes through the I primary of the high frequency trans- ( former, but not through the reaction c coil The high frequency transformer 8 mounting is a four-pin socket similar f to a valve socket, so as to enable the t various transformers to be tried with- ( out difficulty. The transformers em- ? ployed are wound on an ebonite former consisting of a disc half an inch thick » and two inches in diameter, with a slot one-eighth inch wide and one-quarter , inch deep cut in the periphery. Plugs J are fitted to suit the socket. Various * windings have been tried, but the most J successful so far consists of thirty-five f turns of 36 gauge d.c.c. on the primary ? and fifty turns of similar wire on the ] secondary. A .00025 mfd. variable condenser is shunted across the primary f winding. The secondary winding ,is 1 connected to the detector valve through a grid condenser and leak in the usual 1 way. The reaction coil is connected j in the plate circuit of the detector as is also the primary of a low frequency ’ transformer, the secondary of which is j connected to a low frequency amplifying valve in the usual way. The valves used are Phillips amplifiers for both 1 high and low stages, and a Phillips " detector. Separate rheostats are used on each valve, and this seems almost

essential for satisfactory working. The first point noticed when the set was first connected up and tested was that double reaction could be obtained. By tuning the high frequency transformer with the variable condenser the first valve could be made to oscillate quite independently of the reaction coil position. Again the plate circuit of the first valve could he detuned, thus stopping oscillation, and then by bringing up the reaction coil oscillation could be started again. After a little practice it was found that the two methods of obtaining oscillation could be in a sense balanced one against the other, and a very smooth, yet critical, control obtained. It may be said right away that these tests were not made during the broadcasting hours, and interference was thus avoided. After the secret of tuning the reaction circuit had been found, and tests made on the broadcasting stations. It was found that a marked increase in strength could be obtained, but more noticeable was the fact that the reception was remarkably clear and free from distortion. The items from IYA came through with great pureness, the piano solos being especially fine. It was even possible to draw something resembling music from 2YB’s wave, which has been particularly noisy lately. 4YA came through with great purity, while next evening 2BL was heard with good strength. It may be said that this station was not clearly audible previously, using the detector and two stages of low frequency. Static was noticeably diminished and generally the freedom from interference was marked. 1 ‘ The Grid” can certainly recommend anyone with the facilities available to spend a few hours experimenting with this method of amplification. By using a plug-in style of transformer it is possible to make rapid changes, and the tuned anode method of coupling can be used if desired by making an adaptor. Once the secret of the high frequency working has been learnt it is an easy matter to add the necessary apparatus for reflexing, and thus utilise the first valve for two purposes. “The Grid” is following up his experiments and will give further details later. • • • • The Howling Problem. It is understood that the P. and T. Department is instituting a campaign against the howlers who nightly worry the listener-in. In some centres it is stated that letters have been sent to various amateurs pointing out the seri ousness of the trouble, which threatens to become a greater problem than static. It is to be hoped that the matter will be followed up and decisive measures applied. Two possible solutions seem to be to bar reaction altogether, which is too drastic, or to raise the wavelength of broadcasting. The only other solution is to make every amateur use at least one non-oscillating high frequency valve before his detector. This will mean more expense for everyone, but something must be done if anything more than local broadcasting is to be attempted. However, the activity of the P. and T. Department is a rood sirn. and nil ren.sonn.hlp. ama-

teurs should assist the matter in every way possible. Co-operation by the vari; ous radio clubs would no doubt be of material assistance to the Department, since these bodies could help to dispel the ignorance which in many cases is the root of the trouble. • • • • Australian Broadcasting. Reports to hand all state that recent programmes from 2FC, Sydney Farmers, have been extremely enjoyable. This station is undoubtedly the finest equipped in Australasia, possibly even south of the Line, and local amateurs should make a point of obtaining suitable coils for the wavelength, 1100 metres. The coils generally used are 100 primary, 150 secondary and 200 reaction, either Duo-lateral or Giblinremler. The aerial condenser should be in parallel with the primary coil. For those who desire to try home-made coils it is suggested that spider webs be made up, using 30 gauge wire on formers four inches in inside diameter, 75 turns on the primary, 100 on the secondary and 75 on the reaction should be suitable sizes with the average aerial, using .001 mfd. condenser in shunt with the primary and .0005 mfd. in shunt with the secondary. On several local stations quite good loud speaker results can be obtained with detector and two stages of audio frirquency amplification. • • • • Amateur Transmitters. Wanganui has been somewhat backward in comparison with other centres in that we have had no amateurs operating transmitting stations. Certainly the local club was the first club in New Zealand to erect a transmitting station, but this has been used almost exclusively for broadcasting purposes. In Auckland and Wellington much, ink has been spilt over the question of harmonics from the amateur transmitting stations. Broadcast listeners have complained that reception has been marred by amateur morse, while on the other hand the amateurs transmitting strenuously deny that they are interfering. Undoubtedly there is something to be said on both sides, but in Auckland the amateur transmitters rather gained the day when they shut down for a period by mutual agreement, and found that complaints of interference from amateur morse were still received. As a matter of fact most of the interference comes from commercial stations, especially some of the old type ship stations, which have broadly tuned spark sets. The Government stations are also offenders, VLA in particular being easily readable at times on 200 metres. Locally we have as yet experienced no trouble from amateur transmitters, although some unruly spirits occasionally make rude remarks concerning 2AH, but it is possible that in

a short time an amateur station will be erected. It is to be hoped that every precaution will be taken by the operators to avoid interference, and “The Grid” would suggest the use of straight C.W. in preference to chopped CW. for this reason. If amateur transmitters do interfere with broadcasting, the solution is to bar them from working during broadcasting hours on the principle of the greatest good for the greatest number.

The Radio-Liar. The general introduction of wireless has greatly widened the scope of the disciples of Ananias. At one time the fisherman held the laurels for tall stories, but he has easily been eclipsed by the radio-liar. All amateurs know the type; he meets one in the street and promptly blurts forth that he has heard XYZ on one valve, with the ’phones on the back verandah and his head under the bedclothes! Or else the neighbours are complaining that little Willie can’t go to sleep at night because of the loud strains of melody issuing from his loud-speaker. If you go along to his house to hear the wonderful results you will probably find his battery is flat or his aerial down or something else is wrong. If the set does condescend to work you will have to screw the ’phones into your ears, hold your breath and stop your watch before you hear anything. But the radio-liar is quite undismayed he promptly blames some part of the set and enlarges on the terrific strength a couple of nights ago, when nobody but himself was listening! Why is it that a set which was working perfectly the night before can go completely on strike when the filament “juice” is turned on next day? Why is it also that it always goes on strike when visitors come along to hear the music? The radio-liar’s set always seems to have the disease when anyone but the owner is present. Is it the set which is wrong, or is the owner’s vivid imagination to blame? The signals heard a few nights ago, like the fish that got away, seem to gain magnitude with every mention of them. O radio-liars, what a lot you will have to answer for when the day of judgment comes! z General Notes. Owing to Mr. Robinson being indisposed, the usual transmission from 2AH did not take place on Saturday evening. Local amateurs in general, and crystal workers in particular, will joi.* in wishing him a speedy recovery. The short article on “Wireless Widows” published by “The Grid” recently has given rise to much comment. Several of the widows have expressed the opinion that the sentiments expressed were the most sensible that “The Grid” has been guilty of. Opinions apparently differ in this respect since some of the husbands have thread ened dire penalties on “The Grid” if they can catch him. Great are the virtures of anonyminity! There selms little doubt that wives and wireless don’t agree, the main reason apparently being that to operate a wireless set I successfully it is necessary to keep I quiet—and who can expect this of a woman? But even though they arc bound to keep quiet, isn’t it better to suffer this penalty and keep their husbands at home at nights. If there were no wireless sets the husbands would probably be out at the club. Half a loaf is better than no bread, likewise a silent husband at home is better than a noisy one not at home. And after all it amuses the old dears and keeps them out of mischief, doesn’t it? Heard during the past week, 2YK medium strong, modulation rather poor, 2YB mediumly strong, modulation bad, 2YM strong, modulation fairly good, IYA strong, very good modulation, 4YA strong, good modulation, 2BL fair strength, modulation good, but strength of music less than strength of speech; 2FC fair strength, heard on speech only for a few minutes. Other reports, please ?