Longwave Broadcasting

Radio Record, Volume V, Issue 42, 29 April 1932, Page 4

Longwave Broadcasting

aeeeeateetaienet pe Possible Solution to Difficulties Hi investigations of the Coverage Commission set up by the Broadcasting Board will, occording to the chief engineer of Philips Lamps (N.Z.) Ltd., doubtless include a survey of the possibilities of 1500 or 2000-metre broadcasting as a solution to New Zealand’s national coverage problem. The failure of 2YA to give the service expected of it, in certain areas, is well known. There has recently been a revival of technical interest in broadcasting on wave-lengths around 1500 metres. Broadly speaking, the aerial energy of a transmitting station produces pressure waves which travel to the reception point by two different rouyes-one following approximately the tour of the Jand, and known asthe ground -wave, while the other is launched into space at an angle above the horizontal plane, and only reappears on the earth’s surface again due to reflection and refraction from the Heaviside layer. The ground wave provides the useful energy in localities near the transmitter, while the spacé wave becomes of the major importance in very long-dis-

tance reception. At certain distances, and under certain conditions, ground wave and space wave interfere with one another badly and cause severe fading and distortion. The space wave coming by the .devious route is more subject to distuny ances and distortion; it is only becaw®: of its usefulness at comparatively great distances that it is tolerated. It is impossible to secure consistent first-class reception when relying on the space wave. The area covered by the ground ware of station is more a function of wavelength than of power, and there is more or less definite mileage limit (for a given wave-length), which increases of power will not appreciably extend. It so happens that the possible effective ground wave radius is considerably greater for a 2000-metre wave than for, say, a 400-metre wave, so that by adopting a long wave-length it is possible to bring a greater number of listeners within the zone of assured reception free from the distractions of fading and distortion. In general, it may be said that 200-600-metre wayelengths have greater claims for reception at extreme distances, particularly at night time, while 1500-metr@ waves give more consistent and relifible reception at moderate distances-recep-tion under daylight conditions is also considerably improved. It is in these respects that longwave broadcasting is now engaging the attention of radio engineers in various parts of the world.