NAB reports (Mar-Dec 1933)

guarantee a ten kilocycle band width. The ten kilocycle interval between stations was set np originally when we were talking about 5 k. c. side bands. Nevertheless, there are many stations where the studio is located in close proximity to the broadcasting stations, which are actually putting out large range— to 10 k. c. That applies largely to the local stations but at the same time it will apply in the near future to some of these clear channels. I do not believe that we are ever on sound ground on the subject of band widths as long as the average radio receiver is not capable of reproducing bands much above 3.0 or 3.5 k. c. There have been some re¬ ceiving people who say that they have tried wide band receivers and that the public does not want them because it is not commercial. I believe that purely from competitive standards we are going to be forced to meet this situation. We are going to have to do it. “You can see a similar variation going ahead of you in the sound picture field. At the outset there was more won¬ derment at sound pictures than anything else but they have rapidly expanded to the front. The wide range systems are being brought about in the sound picture field just as rapidly. Peopje are going to ask why they can’t get the same quality in their homes. This is another example for you and I still feel that there may be competitive limits which will force us in this direction. You are familiar with some of the experi¬ ments which have been made in connection with the wired radio systems and particularly through the power lines. These people have one big advantage in that they do not have to resort to advertising lines during the program. It will be perfectly logical for them to get wide band transmission with the best of quality. If they do that, you will immediately find yourselves faced with the necessity of following their course, but the reaction on radio would be extremely far reaching. It seems to me that the 10 k. c. intervals between stations is one of the most stable influences in broadcasting today. This has brought out in our review of the broadcast field. I do not believe at the present time that research ob¬ jectives constitute a foundation on which to build. One idea which might deserve consideration is to split the bands from 7500 or from 7000 to 3000 cycles. When you are in the immediate vicinity of a high power station you can tune the receiver noise level down. The local side bands overlap any of this interference and you can now approach 7000 cycle reproduction. When you are at some distance from the trans¬ mitter, however, there is a point where you have to consider adjacent channel stations of somewhat equal intensity and the job would be to close down this band pass to 3000 cycles which is all you are getting now and is a reasonably accepted stand¬ ard. You get then freedom from noise and it is working in practice. “These are just some of the ideas of practical steps that can be taken. One of the problems of this job is to outline the program and nobody can outline the program at the present time. It is difficult to sell some of these people, to give them the picture, because it is not possible to outline the whole program from the beginning. This matter calls for a research undertaking but I think the immediate thing is that we appreciate the necessity of some academic attack on the common objectives of the industry. We pledge our¬ selves to it and while I do not believe that there will be a revolution, nevertheless, I believe that as time goes by and we look back on what we have accomplished and where we have proceeded from, we will regard this movement as one of the most constructive steps that has been taken by the industry. I hope I have said enough to prompt some of you to get on your feet and comment on this thing.” CHAIRMAN : “I think the Engineering Committee fully understands the purposes even if some of the rest of the peo¬ ple here did not grasp that from the way you spoke. I doubt I would ask any questions here.” MR. NELSON : “I have been hoping that somebody would discuss the matter on a half dozen or so angles. Since there has not been a disagreement, there may be something in it after all.” MR. HORN : “A fair standard for transmitter and receiver would help out an improvement in the industry.” CHAIRMAN: “Is there any further discussion?” CHAIRMAN: “I would like to suggest, realizing that it has a great many problems, both technical and political, the idea of transmitting the carrier and one side band.” MR. NELSON : “That is a suggestion which has been ad¬ vanced again and again. There are complications which all of you should realize. A lengthy mathematical derivation of this subject would be in order but I want to give you an angle on some of the complications here. In the first place the carrier, two side band, system is the natural way to do this job. The ordinary carrier is modulated so that the dis¬ tortionless detection is possible. Just as soon as you sub¬ tract one of these components you have taken away something from that wave and you no longer have a distortionless sys¬ tem. Unless you do something you will find you are introduc¬ ing a lot of distortion. In telephone plants where many of this kind are in use, the way it is overcome is to employ a very large carrier in the demodulating tubes because this single side band and the second order terms produce much distortion. Distortion components are in that way rendered negligible. There is a problem you are going to face ; for to employ carriers of large power, we are going to have to have a special kind of receiving equipment not now available. While it is technically possible, I hesitate to adopt it at the present time for some of the reasons mentioned above. One of the merits of this is the fact that we can use existing receivers if you have 3,000 cycle reception.” CHAIRMAN : “If we are going to get out, we will have to limit these discussions. Your Engineering Committee, as Mr. Nelson told you has already had several meetings with R.M.A. concerning transmitter manufacturing and are rapidly working toward a set of acceptable standards. We have can¬ vassed all of the members of the N.A.B. and expect to get answers from them to determine exactly what the broadcast studios want and how they feel about various standards. At our next meeting we hope to discuss a complete analysis .on the existing set-up and the possibility of establishing definite standards in regards to certain specific phases of it. To get on with the program, there has been a great deal of discus¬ sion recently on antennas. Mr. Harmon of Westinghouse Elec¬ tric and Manufacturing Company has a discussion on that, subject.” BROADCASTING ANTENNA DEVELOPMENTS By R. N. HARMON MR. HARMON: “I am going to present a very brief dis¬ cussion of the various typesi of antennas which might be used for various types of problems as they may come up before the stations. I will then answer a number of definite ques¬ tions which may propose a more desirable way of meeting antenna problems in general.” (Mr. Harmon illustrated various antennas and discussed them.) CHAIRMAN : “Mr. C. B. Aiken of the Bell Telephone Laboratories is with us. He will discuss synchronization.” SYNCHRONIZATION DEVELOPMENTS By C. B. AIKEN MR. AIKEN : “Synchronization is about eight years old now. About that long ago we made our first efforts to syn¬ chronize on the same wave. This was done almost con¬ currently in England and Germany and other countries shortly afterward. The English experiments were particularly inter¬ esting because of the experiments of P. P. Eckersley. Captain Eckersley’s first experiments were made on two stations, thirty miles apart in England. We know what synchronization is and have a pretty clear conception of synchronized transmission. We know that it is very closely related to transmission and it becomes recognized that distortion in the mid-air between the two synchronized stations, fifty miles apart, is unavoidable and that there is nothing that can be done to eliminate such distorted reception. The matter is one of field strength. We predict whether or not there should be distortion in mid-air. If there is any slip in synchronization, of course conditions are much worse than they are when everything is as carefully controlled. You have probably heard the type of distor . Page 164 .