LIMIT OF SHORT WAVES

Radio Record, Volume I, Issue 42, 4 May 1928, Page 13

LIMIT OF SHORT WAVES

T has now been definitely established that with ordinary receiving and transmitting valves it is impossible to work on wavelengths of less than about two metres. . This rather contradicts several of the rumours which were current when amateurs first became interested in super-short-wave- working, and many almost impossible claitns of suecessful workjing on one and even half a. metre were made, : . Valves Set a Limit, Valves set a definite limit to the minmium wavelengths workable, for below a certain range (usually about, ten metres) the capacity of the elec trodes becomes too great to be balanced out. The size of the electrodes may be reduced a little to lower the capacity effect they present, but the mass cannot be cut down too far or the valve will not function. Need for Accuracy, A wavelength of 5 metres means a frequency of 60 millions of cycles per second, and the need for accurate tuning adjustment will be obvious. As an instance of the extreme care necessary in adjusting ultra-short-wave sets, it may be mentioned that in 5-metre experiments conducted recently at WGY, Schenectady, the actual transmitter was placed in the centre of a Hertz-type. aerial (a vertical wire, one half of which is aerial and the other earth) and tuned by ropes from a distance of approximately 100 yards.