Wireless Broadcast

Star (Christchurch), Issue 17780, 25 February 1926, Page 11

Wireless Broadcast

CONTRIBUTED BY

“AERIAL."

LISTENING FOR, WRVA

PROGRAMME FROM AMERICA. Recent cablegrams from America announce that on February 27 a new American broadcast station will transmit a special programme, in an attempt to reach New Zealand and Australia. The station is owned by the Edgeworth Tobacco Company, Richmond, Virginia. The call sign is WRVA, and the station is reported to be the last word in radio, the transmitter and studio being equipped with the very latest apparatus. Since being put into commission on November 1 last, the programmes have been heard in many parts of America, Canada and Mexico. For this special programme, a wavelength «of 256 metres will be used, and the transmission will take place from 4 a.m. to 6 a.m., eastern standard time. The corresponding New Zealand time is approximately from 8.45 p.m. until 10.45 p.m. on Saturday, February 27. In view of the fact that WRVA has a very powerful transmitter, and the wave-length to be used is comparatively short, there is a very good chance that those who possess sensitive, receivers will receive part or the whole of the programme. There should be no interference from other stations in New Zealand or Australia, as there are no stations operating within twenty metres or so of WRVA’s wave. The one thing to be feared, however, is interference from howling valves. Any receiver which is not equipped with at least one stage of neutralised radio-fre-quency amplification is almost sure to cause trouble to others if it, is used in an oscillating condition. This applies very much to ordinary three-cir-cuit receivers, such as honeycomb coil sets, or variometer receivers. So’ in fairness to the other fellow considerable care should be exercised during the tuning-in process, and if it is found impossible to "clear up” the signals from WRVA, it would be a good idea to try for some other station. A very simple way to determine whether the receiver is causing trouble or not is to moisten the finger and touch the aerial temiinal, or the wire leading to the grid condenser. A click may be heard as the terminal is touched, in which case things are all right; but if a click is heard in the phones when the finger is removed, then it is certain that someone is hearing a carrier wave from your receiver, and is saying some very hard things about you. The fact that the coupling between the primary and secondary coils of a receiver m "quite’Moose” is no proof that energy is not being sent out from the receiver. The writer has seen a receiver using honeycomb coils, with the primary and secondary coils over five inches apart, induce sufficient, energy into the aerial to cause a good whistle in a receiver four miles distant, and in fact, on this adjustment, a message was sent, the message proving that the origin of the received whistle was in the honeycomb coil receiver. This simply shows the extreme care necessary when tuning-in to avoid “blooping” the other fellow 7.

ALARM BY RADIO.

WARNING OF BUSH FIRES. Now that the hot weather is being

accompanied by bush fires in almost every part of Australia, the broadcasting stations are sending warnings as occasion arises, informing listeners where fires ha\-e occurred, and the direction in which they are travelling. Recently the Melbourne broadcasting stations ii terrupted the transmitting of their church services to make knowm that the townships of Lilydale, Ringivood and Doncaster East were ened by fire, and to call upon volunteers to turn out to check the outbreak. Already instances have been reported of the value of the S.O.S. call, and within the last month a resident of Eastwood, N.S.W., whose house was destroyed by fire during his absence, received notification of the fact whilst listening in. The Radio Broadcast Bureau has been informed that a line of ’buses plying between Mittagong and Moss Vale are being equipped with threetube receivers. This is largely due to the value of radio as a fire-fighting agent, as the proprietors of the ’buses consider that if the police advise the Sydney broadcasting companies regularly of the outbreak of bush fires the companies can systematically call for assistance to specific locations and so bring help to struggling settlers.— "Wireless Weekly,” Sydney, February 12.

JOTTINGS.

Most authorities agree that resistance capacity audio amplifier gives more natural reproduction than does the transformer coupled amplifier, but to give good results the resistances themselves must be very good. Those which use compressed powder or paste as the resistance element are often very noisy and inferior to the wirewound resistor. A wire-wound resistor can be made at home by taking a three-inch length of ebonite rod, two inches in diameter, and having eight slots, each 1-10 inch wide and a quarter of an inch deep cut in it. Then wifid thirty turns of No. 47 d.s.c. Eureka resistance wire in the first slot, and a similar number in the second slot, and in the same direction. Then wind another 30 turns in the first slot, this time in the opposite direction, and do the "same again in the second slot. When the first two slots are wound, proceed with the next two, repeating the operation. This reversal of direction of winding makes the resistance practically non-inductive. The resistance of No. 47 Eureka wire is given as 214 ohms a yard, so it is an easy matter to know how much wire to use for a desired value of. resistance. Suppose each slot, with its sixty turns of wire used eight yards, the resistance worfcS out at approximately 1712 ohms per slot. The figures given, however, do not represent any actual case, but are given merely as a guide. 35 35 35 The annual meeting of the Radio Society of Christchurch was held last Thursday evening. The balance-sheet showed the society’s affairs to be in good condition, and the reports indicated that some useful work had been done. The newly elected officers of the society are as follows: President, Mr H. Macintosh; vice-presidents, Messrs W. H. H. Downer and E. W. England; secretary, Mr V. Larson; assistant secretary, Mr F. Vincent; hon treasurer, Mr H. P. V. Brown; hon auditor, Mr H. Metcalf.