NOTES AND COMMENTS

Sun (Auckland), Volume 1, Issue 71, 15 June 1927, Page 14

NOTES AND COMMENTS

LOSS OF “UNCLE JACK” The taking off the air of Mr. Prentice is one of the most unsatisfactory features of our present broadcasting. The extent to which he has endeared himself in our Auckland homes was brought to the writer in a way which must surely have been overlooked by the management. A city man on arriving home at 8 p.m. on Friday evening found a distracted wife consoling two small children, the cause of whose distress was the fact that Uncle Jack had not spoken to them during the early evening session. This gentleman, who had been tolerant of “the finest broadcasting service in the world,” was now openly critical and, rather illogically, but very forcibly, demanded that something should be done. This

UNCLE SAM, who tells fairy tales to the children from IZB broadcasting station every Monday evening. may be an isolated case, but it may not, and as to what can be done it is doubtful as both parties refuse to discuss the matter. Many members of the Listeners’ League consider that the opportunity is ripe for a public meeting to discuss the whole situation, and the executive of the A.L.L. should remember that if members want this meeting now is the opportunity as never before has the public been so acutely interested, and the public is a fickle jade. WAVE TRAPS Many listeners whose sets are not sufficiently selective to cut out the local station have thought of adding a wave trap to help cut out the interfering station. It must be remembered that highly sensitive receivers will be less selective than a less sensitive one, and in this case the remedy is a reduction of the wave pick-up system. Improved selectivity is got mainly in four ways.

A succession of tuned circuits may be coupled to one another, and the desired signal energy, as well as the undesired signal energy, may be caused to traverse the successive circuits. The attenuation toward off tune, that is, unwanted currents, may be considerably increased in this fashion, and the selectivity improved. The next method is a succession of tuned circuits, each more or less independent of the preceding one. Such circuits are generally separated by valve repeaters, whose back coupling requires to be neutralised. The attenuation toward off tune currents is the sum of attenuation due to each of the circuits, and the overall selectivity may reach a high degree. The third method is the use of an intermediate frequency selectivity in addition to the above methods. This will be recognised as the method used in the super heterodyne receiver. Finally, we have a tuned circuit which may precede or follow the set without any alteration. This is the wave trap as it is commonly known. An interference reduction service was conducted in America in which complaints were analysed, instructions given and if the instructions failed when applied by the set owner he was visited by an official and the results were as follows: Satisfied after visit .. 63.6 per cent. Fixed own trouble . . . . 6.6 per cent. Bought new sets . . .. 7.4 per cent. Partly satisfied .. .. 5.6 per cent. Dissatisfied 2.3 per cent. Irrelevant 14.5 per cent. The interesting part follows: “In the great majority of cases the interference can be eliminated by the use of what is called a series wave trap.” As this trap, which will be described below, was successful in the case of interference in the viciinty of a 50kilowatt station, a station one hundred times more powerful than our local stations, the reader may draw his own conclusions as to the sharpness of the tuning of IYA from his own results with this trap.

Connect a wire up coil as per d agram, connect “aerial’ of set to 30, Urn tapping, set trap condenser at zero and tune in some desired station. N<te this may come in at a new setting on the left-hand condenser dial of the set. If the interfering station is now heard as well as the desired . one. .turn the wave trap condenser till the interference disappears. If the desired station disappears altogether with the unwanted one, change the tapping to the 18th turn and so on to the 10th and sth taps. If with the tap on the 30th turn the interfering station can still be heard under the desired one, change to the 60th tap and repeat. A .0005 fixed condenser connected between aerial and earth terminals on the set may help materially. NEW APPARATUS REVIEWED BY THE SUN From time to time THE SUM proposes to review new apparatus sets, etc., and will give an impartial report on their own experiences with the apparatus under review. The Radio Traders have been approached, and THE SUN hopes to give its readers the its experience. POLAR TWIN The set was carefully packed in a carton and complete with coils, valves and connecting wires. The valves were tested for emission and filament current under working conditions. Voltage of filament, 2. Voltage of plate, 90. Total filament current, .21 amperes. Detection emission, 2 milliamps. Audio amplifier, 10 milliamps. The set was connected up as per instructions, and there seemed a dinger of mixing the A and B batUQr leads unless one read the instructions carefully and which a person overeager to get the set working might easily not do. These leads are distinguished by a green binding for the A battery and a yellow binding for the B battery. Something more is wanted, I think, either the binding might be labelled or a pictorial instruction sheet might be supplied. With a good aerial IYA was good loud-speaker strength; 2BL wa.s next tuned in with a slight background of IYA, which was really very good considering the circuit used. 2BL gave nice loud-speaker volume for a sitting room. After 10 p.m. 2FC and 4QG were tuned in at about the same strength as 3BL. The reaction adjustment is quite neat and the set has the virtue that if it is made to oscillate the operator can get nothing himself in the way of intelligible signals and so the set should ca.use no trouble to others. The tone was excellent and should be as a high quality transformer made by one of the world’s greatest scientific instrument makers is used. In brief, the whole set should appeal by virtue of its economy in working and its results, which are excellent for two valves, and its ease of control. The appearance is conventional English practice, rather unusual to our ideas, but space hits evidently been a big factor in the design. jg Ipg -ft Wr g a-**#** ON THE AIR Broadcasting programmes will be found on Page 16. 6 7ir Jr rfc -Jr & rfc Vfc