Radio Broadcast (May 1928-Apr 1929)

AS I H t kkOAnr.AVI hk SVVKJ] Broadcast Frequency Characteristics A QUESTION of importance is brought up by Mr. F. H. Akers of Chicago in the following communication: There is, I think, a growing tendency among the broadcasting stations, at least around Chicago, against which I should like to raise a "squawk." 1 have been noticing for some time an increasing tendency for articulation to become poor and a general inability to hear spoken words distinctly. At first I looked in the set for the trouble but was not able to find it, and, checking up with other sets and with a friend working at a broadcasting station, 1 found that they are favoring the low audio frequencies so that their station will sound better on sets with poorer audio equipment. This seems to be a growing practice which, of course, is nice for the fellow with a poor audio amplifier, but leaves the quality not so good for the listener with fine equipment. Perhaps others are having the same trouble and are mystified at not being able to find the cause. In the long run I do not believe such practices will be good for broadcasting, because they discourage buying good receiving equipment. I do not know to what extent this is being done, as the better and larger stations do not do it, and I may be wrong in my conclusion. I have not run across cases of intentional frequency discrimination at broadcast stations, such as Mr. Akers complains of, and doubt their prevalence in the Chicago district or elsewhere. Of course, there are numerous instances of failure to transmit essential frequencies in the audio band, but these are seldom purposeful, and may as a rule be ascribed to poorly designed or badly operated equipment. The case reported in this department about a year ago, where a station operator connected a half-microfarad condenser across an amplifer to get rid of microphone hiss, and incidentally cut out most of the tones above 2000 cycles a second, is a flagrant instance, but quite extraordinary. In this case the owner of the station liked the absence of high frequencies; it made the music " mellow," he said. He should have a dozen cheap violins smashed over his head before being handed over to the constabulary. Violins are rich in high-frequency partials. A few years ago, also, a New York station broadcast from a sea resort about eighty miles distant over an unequalized wire line. The result was about the same as in the station which eliminated carbon "rush" by the inspired-expedient aforementioned. Many stations, of course, transmit only the three middle octaves of music, and the Federal Radio Commission lets them stay in business. But these are all effects of ignorance or inadequate technical facilities. The stunt which Mr. Akers describes is a different kind of offense. If anyone has actually thought of such a device, I agree with our correspondent that the inventor had best put the idea in his cold file and forget it. Compensation in one link of an electro-acoustic chain for the defects of another section is of course no novel idea, and in some cases it is a justified, although always somewhat dubious, design resource. Something may be said in its favor when it happens to be economical and when the defects to be ironed out are quantitatively known, so that a precise compensation is possible. But receiving sets may have so many different defects that any attempt at correction of the audio characteristic at the transmitter is bound to injure as many listeners as are benefited for the time being. If the lows are allowed to predominate at the broadcast station, what is going to become of the people who have drummy receiving sets, not to mention those who have already attained a reasonable flatness in acoustic design? There is as much logic in making the station output tinny in order to help people whose receivers are down at the high end. If the stations went in for this sort of thing the audio-frequency spectrum would become as disorderly as the radio, which heaven forfend. Let the manufacturers of receivers, amateur and professional, strive for audio characteristics flat between ioo and 6ooo cycles, and let those of the broadcasters who have not yet at tained this reasonable ideal bend their efforts in the same direction. Plenty of the broadcasters are already ahead of this standard. I offer in evidence Fig. I, a curve of the frequency response of the National Broadcasting Company's weaf transmitter at Bellmore, Long Island. The station was built by the Radio Corporation and the transmitter supplied by the General Electric Company (Advertisement). The observations for the curve were made by Mr. Raymond Guy, and I will vouch for them as authentic. That is a pretty curve, and for practical purposes it would be no better if it were a horizontal line drawn with a ruler between 30 and 10,000 cycles, because the irregularities in the characteristic are too small for the most sensitive human ear to detect. Alas, not all of this lovely curve is utilized by the stuff which gets out over the wire line. I reproduce it, however, so that Mr. Akers may feel assured that some broadcasters strive to let the efforts of the artists go out to the world without any acoustic infidelites. Those who do not at least make that effort are, I believe, in a very small minority. Low Voltages are Dangerous WE HAVE certainly stressed the danger of coming into contact with high-tension conductors in broadcast stations frequently enough in this department. Perhaps not enough has been said about the menace of rerelatively low-voltage circuits. The following account of a most unfortunate accident, through which a well-known telephone and radio research engineer lost his life, may give pause to those who think nothing can happen to them on 1 10 or 220 volts. The clipping is taken from the New York Times of April 13, 1928. Deal, N. J., April 12— H. R. Knettles, 31 years old, a member of the technical staff of the local Bell Telephone laboratory, was killed early to-day when he came into contact with a low-voltage power circuit. His body was found on the floor by other members of the staff. He had entered an enclosure in which the only electric power was a 240-volt alternating current supply, and was probably killed, it was said, when moisture in the air caused a short circuit with his body. Pulmotor efforts at resuscitation failed. The seriousness of an electric shock is dependent, of course, on the power dissipated in the victim's body, rather than on the voltage impressed. The "medical" induction coils which were popular ten years ago used to generate several thousand volts, but the available power limited the current to a few milliamperes, so that no damage to tissue could result. When the power is not so limited, and the resistance presented by the body happens to be low, moderate voltages may cause death. Every year a sizable number of persons are killed in bathtubs on 1 10-volt circuits. Standing in water, and with wet hands, they touch a defective electric light fixture. Under these conditions the resistance of the body is reduced to a few hundred ohms. The resulting current may be of the order of an ampere. Any considerable fraction of an ampere, especially when it passes through vital organs or nerve ganglia, is likely to cause grave injury or to kill outright. In handling high-power, highvoltage circuits, in general, contact means certain death. In the case of high-power, lowvoltage circuits one gambles with the electrical resistance of one's body. If it happens to be low a few hundred volts will send a man to eternal sleep just as surely as a few thousand. The story about moisture in the air, in the case of Mr. Knettles, is, of course, a reporter's misconception. Apparently the engineer came into contact with the conductor through his head, which may have been moist. Anyone who has ever made a good contact with a 220 or 240 Frequency Response Curve of Bellmore Transmitter 1 100 1000 10,000 FREQUENCY, CYCLES PER SECOND FIG. I 219