Local Reception

Radio Record, Volume V, Issue 14, 16 October 1931, Page 30

Local Reception

Ultra Shortwave Broad"casting "THE desire of broadcasters to be heard over as wide an area as possible has caused a large amount of unnecessary interference, due to the limited number of channels available on the broadcast band of wavelengths and the extraordinarily long range transmissions of many of the higher powered stations. ; The problem has become an acute one in countries where broadcasting stations are numerous and remedial measures are being urgently sought. Recent advices to hand from the Technical Department of Philips Lamps (N.Z.), Limited, indicate that extensive experiments are being carried out on wavelengths around 7 metres. At these very short wavelengths the number of broadcasting channels available becomes very much larger, for example, staggering as it may seem at first sight, there are as many channels available between wavelengths of 7 metres and 7.16 metres as on the whole of. the broadcast hand--i.e., -200550 metres, or between 7 metres and S metres there are no fewer than fire and a half times the number of channels on the normal broadeast band. Seven metre wavelengths have, however, another very noteworthy property which limits their effective range to some 10 to 12 miles-and it is practically impossible to hear any 7T-metre station outside this radius. This means that stations separated by only 50 miles distance could transmit on the

‘game wavelength without possibility of mutual interference. Low power is quite effective; in fact, increasing the power a hundredfold or a thousandfold does not effectively increase the coverage area, "The receiving apparatus is simple and cheap, and for purely short range broadeasting these 7-metre developments will be well worth watching. One of the pioneer stations is PFPF, on a wavelength of 7.85 metres.