COMPARISONS OF POWER

Evening Post, Volume CIV, Issue 24, 28 July 1927, Page 18

COMPARISONS OF POWER

Much curiosity has been aroused among owners of receivers using several valves by the fact that the Auckland and Christchurch stations give just as much volume of sound as the Wellington station. This applies to listeners here and in parts of the' country far removed from Wellington. In some places the new Wellington station has been criticised, on the ground that it is evidently not so much more powerful than the other stations as has been represented.

The evidence on which such a conclusion is based is wrong. The relative strengths of powerful transmissions cannot possibly be judged by the use of an ordinary largo broadcast receiver without special precautions.

The output of a receiver is limited. If the audio-frequency amplifier is of tho capacity usually put into broadcast receivers, tho limit of output is fixed by the last valve and is reached when that valve reaches the overloading point, the exact stage at which this is reached depending upon tho users' tolerance of unpleasant noises. If the amplifier is a really powerful one, the overloading point may be reached first by another valve than the last, probably tho detector. Now it is quite easy, with an efficient radio-frequency amplifier, to "fill" a detector or am-n-1 T alvo in receiving Auckland and Umstchurch transmissions. The output then is all that the set is capable ot producing, and a more powerful transmission can make no more volume of sound come from the receiver except at the cost of overloading. . If it is desired to make a direct comparison between the strengths of two stations, they must be tuned in without altering any of tho adjustments of the leceiver, and the receiver must be of a *pc m which there is no regenerative effect, and in which the amplification is so small that the weaker station is only weakly heard. Even then the B J pawson will only be a rough one. Exact, comparisons require very careful observations with special apparatus!