NAB reports (Mar-Dec 1933)

Record Details:

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dons complicated problem that you have. In order to deter¬ mine what constitutes acceptable signal intensity, or what constitutes tolerable interference, and what are the frequencies that should be allowed in broadcasting, and what frequencies should be used in a practical combination of distance and other rules of these problems, involve in one passing day a great variety of other problems, psychological problems and practical problems. These factors are all very complicated in the particular one which I wish to discuss. “It appeared, from the preparatory work for this North American Conference that it would be desirable to get as clear a statement as might be possible of that one side of the prob¬ lem — the physical facts, — and that was done by a small com¬ mittee that was appointed in connection with the preparation for the North American Conference. That committee has turned out a report which sets forth an issue which I think will be of use to you. It turns out to be more clear and dis¬ tinct than we hoped at the start. ‘ ‘ There has not been any place to which you could turn to find out definitely the specific relative values of the various frequencies of the broadcast band and the frequencies adjacent thereto. It has become possible to take known facts and give you a definite answer to those questions. A little work of this kind was done at the Madrid Conference and it was thought that it would be helpful if some definite statement be compiled to give the actual field intensities at the fre¬ quencies concerned in broadcasting. The results of that work are contained in a paper published in the July issue of the Proceedings of the I. R. E. This report of the American Committee which I am talking about will also be published later in the Proceedings. “This American Committee has developed the subject con¬ siderably further. What we did was first to cheek available data and plot curves giving the field intensities at distances from zero to 6,000 kilometers and frequencies from 150 k.c. to 1700 k.c., those being the limits of the range in which you are presumably interested. This work also includes figures giv¬ ing the variation with frequency for interference with recep¬ tion of signals caused by static and other noise such as elec¬ trical interference, receiving set noise, etc. The data included in this report are based on all the facts we could get our hands on. Data has been obtained both in this country and in other countries and covers all of the theoretical work that has been done. A number of things stand out and I will just mention a few of the high spots. In the first place you have to untangle the difference as between day propagation and night propagation. Up to a certain distance in the daytime, the transmission is only ground wave transmission and for night, ground wave transmission conditions are pretty uniform and we put down definite curves giving the intensities at the various frequencies. It is those ground wave curves which give you values which vary with the different frequencies. Ground conductivity varies from sea water to the worst ground conditions we have. It turns out from the data we have col¬ lected that the distance of transmission at night is independent of ground conductivity and independent of frequency and that is distinctly brought out in the data that we compiled, and seems to be quite well substantiated. ‘ ‘ The day and night distances vary from about 40 kilometers for the lower conductivity and the higher frequencies to about 400 kilometers for the higher conductances and the lower frequencies. At greater distances than those, the sky wave predominates and the ground wave is negligible at the receiver so that it fades both day and night. We have some data showing that and it seems to be a reliable conclusion. To this fading distance both day and night, the received in¬ tensity approaches ground values. The report giving this com¬ pilation, we also have plotted the field intensity curves on a larger scale for the short distances. For distances up to about one hundred and fifty miles the curves show the received in¬ tensities for the various frequencies. These curves will be of use to you in collecting service areas data and that sort of thing. As I said they are pretty reliable and you can apply them to any particular example and you will find that they cheek. I might summarize that in this part of the data we assimilated some rather complicated sets of phenomena and the few points I have mentioned, together with the curves en¬ able you to cheek phenomena and write down something which will apply and give you some actual facts for propaga . Page tion in different cases. When you come to consider the limita¬ tions imposed by noise and the very seriousness of noise, the problem is even more complicated. By cheeking such facts as wo have, as I said, we have worked out curves giving the dis¬ tance at which you get a useable signal for various values of noise level, which corresponds to various localities for various assumed regions signal intensity to noise, for different powers. “Mr. Chairman, to go into any further detail of the matter of data available on this acceptable signal for different regions of signal intensity to noise, etc., would take ten or fifteen minutes. I am not sure whether it would be desirable to do that. Perhaps it might be well to terminate my presentation here and I would be glad to carry on further if it is interest¬ ing to you. ’ ’ CHAIRMAN: “You said the curves are available?” DR. DELLINGER: “The report of this committee was sent out by the Federal Radio Commission and I presume that they have some copies for anyone who is especially interested. The document has been sent in to the Proceedings. Just what particular issue it will appear in, I do not know. ’ ’ DR. JOLLIFFE: “As far as copies are concerned, we have a very limited number. ’ ’ CHAIRMAN : “I think that answers a lot of questions on frequency valuation and points out a lot of things quite clearly. We are all interested in being able to secure the in¬ formation. Before we go into this next discussion, which I am sure will break up the meeting, I want to get a picture of the entire group.” CHAIRMAN: “Gentlemen, this next subject is of great interest to a number of people. It has been put on the pro¬ gram because it has been discussed quite a bit and promptly everyone began writing about it. The subject is power in¬ creases for local and regional stations and may go on for several hours. It is now eight minutes of one. A motion to adjourn now for luncheon is made; possibly you would like to go right into the discussion of it. ’ ’ Upon motion, it was decided to continue the meeting. CHAIRMAN: “Mr. Bridges WEBC will open the discus¬ sion. ’ ’ POWER INCREASES FOR LOCAL AND REGIONAL STATIONS By W. C. BRIDGES MR. BRIDGES: “I am here as an advocate of higher power on regional channel frequencies, because of a conviction that only through a substantial increase in power will we be able to continue meeting the demands put upon us by our present audiences. “Unquestionably, regional stations have suffered a loss of many listeners since the general advance by cleared channel stations to 50 kilowatts. If nothing is done, I am convinced that we shall soon find ourselves in more difficult circum¬ stances. Under the American plan of broadcasting, we are largely dependent on advertising revenue to meet the cost of operation. This being true, when a station finds itself with income reduced, due to lack of advertising, eventually it will have to cut costs. This will be rapidly reflected in the quality of service. As the quality of service falls, listeners tend to look elsewhere for what they have come to expect, and the advertisers remaining will soon be found spending less money with the stations thus affected. “I am not suggesting that cleared channel stations be limited as to power, or otherwise regulated beyond what is true of the present. However, with standards of performance changed, since the Federal Radio Commission set 1 kilowatt as the upper night-time limit on regional frequencies, our position as a group has been placed at a disadvantage due to the fact that cleared channel stations have been able to mul¬ tiply their original figure of 5 kilowatts. “Broadcasting is now an established medium for advertis¬ ing. It is no longer an experiment, and, therefore, has its place in modern business. But old claims for coverage will have difficulty in standing up under field strength surveys, not to mention listener-preference investigations. These surveys 167 .