SHORT-WAVE NOTES

Radio Record, Volume I, Issue 25, 6 January 1928, Page 12

SHORT-WAVE NOTES

To avoid radiation as much as posSible, the aerial and secondary coils should be loose-coupled, and the aerial c:rcuit should not be more in resonance with the secondary than necessary. ""Dead-spots" may originate . from nearby electric light wiring, choke-coils, Wwave-ineters, etc. Any circuit in resonance witli:a receiver may be, detected at a distance of several feet. ""Dead-spots" are seldom encountered if a long aerial is used, which should be the case if greater volume and DX are desired. Loose-coupling reduces the ‘‘dead-spot" effect, and a method of getting rid of them is to change the length of the aerial or use a small series condenser. Close-coupling of aerial and secondary prevents the detector from oscillating easily This is a frequent difficulty witht novices, The detector tube is of great importance if sensitivity, proper regeneration, and a minimum of noise are required Some vaives regenerate with a hum, others with a click, and still others with a gentle "hiss. The grid-leak may influence this to some extent, but generally speaking, only the third type of tube should be emploved where quiet, sensitive reception is desired. A good valve with a socket that will not allow microphonic "ringing" (especially noticeable at the higher frequencies) is certainly a big step towards proper receiver operation. The value of the erid-leak is usnally very much higher than an ordinary breadcast wavelength Country listeners will be interested to hear of the appearance of a Mullard two-volt super-power valve. In the last audio stage the valve handles powerful signals with ease, thus allowing greater volume withont distortion. This valve, the P.M 252, will probably shortly be ou, sale in New Zealand.