Heterodyne Interference Increasing Reports Wanted from Listeners

Radio Record, Volume V, Issue 5, 14 August 1931, Page 3

Heterodyne Interference Increasing Reports Wanted from Listeners

HEH number of reports on ‘ heterodyne interference received in each week’s D.X. mail has’ increased lately to an alarming extent-so much so that it is apparent a reallocation of at least several

of the Australian and New Zealand broadcasting station frequencles is urgently required. The problem, however, is not as simple as it appears. For instance, in one locality two stations may heterodyne badly, but in another depending on the relative distances from the two transmitters, they may be received separately and without interference. Hence it is apparent that if the best possible re-arrangement is to be made, some idea of reception conditions in various localities is a vital necessity. This is where members of the D.X. Club and listeners in general can perform a valuable service to the radio public of this country. It is proposed to ask every listener to forward to these offices a concise report on the heterodyne interference experienced in his or her particular locality. When sufficient reports have been reteivedand we hope to obtain at least five hundred, covering every locality in New Zealand-all data will be correlated and a detailed comprehensive report prepared. A copy of this will be submitted to the broadcasting authorities of this country, while another will be forwarded to the Australian authorities, who, in the interests of their own listeners, will no doubt be pleased to cooperate. | Every listener who is troubled in this way is earnestly requested to send in & report-for without sufficient data no good could be achieved. What is Heterodyning? OW for those who do not know what heferodyne interference is. Without going into theoretical detail, it is sufficient to say that a heterodyne hetween stations is evidenced by a persistent, usually high-pitched, whistle which ot be eliminated. Sometimes a garbled mixture of, for example, music and speech might be heard. That is heterodyne interfer- | ence. o points to be very careful of, théugh. If your receiver uses reaction you may get a pseudo-heterodyne effect by advancing the reaction control a Bittle too far. A high-pitched squeal is the result. If by slackening the reaction. control, however, this disappears, the whistle is not due to a heterodyne. A receiver should never -be foreed beyond limits in this manner besause of the interference it creates. ; Again, some other listener may be forcing his receiver in this way, with the result that a whistle which persists until the oscillating receiver is re-

adjusted is heard. Do.not mistake this for a heterodyne. One way to make almost certain of the cause of interference is tv listenin to the heterodyning stations at the same time for several evenings. Perhaps the surest test of all, however, is to identify definitely the two interfering stations. In this way all possible doubt is removed. The Report. [N making out the report, it is important that no mention be made of heterodynes between stations which ure too distant or too weak to be of. any entertainment value. . Only when

you locate a station which, if it were not heterodyned, would be loud enough and static-free enough to enjoy, do we want reports. Secondly, heterodyning between stations which are both outside New Zealand or Australia obviously cannot be rectified, and hence details of such would be useless. If one of the stations is in New Zealand or Australia, however, and one in another country, such ag America, a report would be welcomed, After locating a heterodyne which cannot be eliminated without cutting out the station it is desired to listen to, the interfering stations should be identified, not by assumption, but by

listening for the callsign until no possible doubt exists. It is not sufficient to identify a station heterodyning with another as XYZ, because your call-book states that XYZ is on or near the same frequency. If the heterodyne is loud enough to spoil the programme, both stations can be identified. In general, heterodyning occurs between Australian and New Zealand stations. The latter can usually be easily identified, if not during the evening, then at closing time, which in general is between 10 and 11 p.m. As Australian time is 14 hours behind our time, stations in that country can be identified best after our own stations have closed down. The heterodyning stations should be grouped in twos or threes, as the case may be, with call-sign and location given for each. Next, your locality should be given, Country listeners should also give approximate geographical position with respect to the nearest large town. Jor example: "Urenui, 20 miles north-east of New Plymouth." Lastly, state the make and model of your receiver. Those using home-built sets should state the number of tuned radiofrequency stages employed (if .any), with. comments on selectivity. Mark your summary "Heterodyne Interference Report," and forward it to the D.X. Editor, Box 1032, Wellington. Reports may be included with other correspondence, but should: be drawn up on a separate sheet of paper. Reports should be forwarded as soon as compiled, but not before the sender is completely satisfied that the identification of stations is correct. In conclusion, we hope that .every listener will help in. this matter, be« cause it is only by ‘so doing that you will be able to enjoy programmes free from heterodyne interference.