ANSWERS TO CORRESPONDENTS

Radio Record, Volume I, Issue 6, 26 August 1927, Page 14

ANSWERS TO CORRESPONDENTS

"Puzzled" asks for an explanation of Why he can receive 4YA in two positions of the dials on his five-valye neutrodyne. lt was what is known as a "harmonic’' that was being received in the unusual position towards zero. Wireless vibrations behave much in the same way as the vibrations of sound in the matter of harmonics. The second harmonic is the strongest; and received at exactly half the wave-length in metres of the transmitting station. Thus the second harmonic of 4YA would be at 231; metres, and that is why a New Zealand station was found among the American stations. Quite a strong harmonic of 2YA can be received on a shortwave set at 70-60-53 metres. Most of the interference by morse on the wavelength of 8YA is owing to its nearness to the harmonic (300) of VLW’s 600metre transmission. ‘Ihe harmonics are simply sub-multiples of the fundamental wave-length, so that dividing the fundamental by two gives the second harmonic, by six gives the sixth, and so on. From the district north of Gisborne comes an inquiry regarding pusli-pull amplification. Upon making inquiry in Auckland regarding such equipment, tle firm in question informed our cotrespondent that they were sold out of Pye push-pull transformers, and had not replaced them on account of a considerable change being expected in this method of amplification. Probably this statement refers to the fact that pushpull transformers are now being constructed upon limes following the more modern type of ordinary low-frequency transformer, whereby the output of power valves may be handled without distortion. Without such improvement the push-pull method would probably not have much advantage over the latest power valves with straight transformer coupling.