NAB reports (Mar-Dec 1933)

better jol> than the average. Still, appearances are that we are not giving trade area coverage. “The remaining possibility is that the signal reaching the listener is not adequate for the kind of service we are supposed to give. When an advertiser engages the services of our sta¬ tion, he expects the station to bring his message to his cus¬ tomers or potential customers clearly and understandably at the time he contracts for. The advertiser cannot be expected to anticipate times when portions of his customers or listeners will be unable to receive his message, because of local inter¬ ference, and contract for time accordingly. The advertiser selects the time when he believes he will have the attention of the type of audience most interested in his product. It is the job of the station to bring the advertiser’s message to all listeners in the trade area of that station well enough to override local interference, so that these listeners may listen to the advertiser’s message if they so desire. And this must be possible at any hour of the day or night. “Extensive observations convince us that when using an antenna input power of 1 kilowatt, the true service range or where our signals can be received absolutely, is about 1% miles, or a field intensity of greater than 100 millivolts per meter. We find that we give fairly good service up to a point where the field strength drops to 25 millivolts per meter, which is about 5 miles. At points where the field strength is less than 25 millivolts, the listener may listen to us and he may not, depending on the extent of static and induction noises. The advertiser may reach customers outside of the 5 mile circle, and he may not. Remember, I am speaking of goocl noise free service. That is the kind listeners expect, and that is the kind of service radio advertisers are beginning to ex¬ pect and the only kind they are going to continue to pay for. “We give good service up to 5 miles, with an antenna in¬ put power of 1 kilowatt. Some of the heavily populated suburbs of the cities in which we are located are 10 miles from our plant. The trade area of these cities has a radius of about 75 miles. For us to expect to increase our power output so that listeners on the outer edge of our trade area circle receive a 25 millivolt per meter signal, is a little beyond our present hopes. However, such service appears to be the ultimate, and any step toward that end is a step in the right direction. “It is our feeling that if, as the next step, we could move the 25 millivolt line out so that it at least includes the cities in which we are located, we could be temporarily relieved of the pressure being brought to bear on us by listeners and advertising clients. This would mean a five-fold increase in power. Our present power is 1 kilowatt night, 2% kilowatts day. A five-fold increase would make 5 kilowatts night, and 12% kilowatts during the day. “Now I want to point out why increased power to regionals will not create an undesirable situation. I am told that when a station increases its power, the blanket area of that station expands and the station becomes a nuisance to a greater num¬ ber of listeners. As many regional stations are now located near the centers of population, this may seem, at first thought, to be an obstacle in the path of high power. I have been told that the blanket area of a station is the area around the sta¬ tion where the field intensity is greater than 100 millivolts per meter. I am also told that blanketing means that a sta¬ tion ’s signal arrives at the receiver with such intensity that the set cannot tune that station out within plus or minus 50 kilocycles of that station’s frequency. Personal experience shows me that when using a modern receiver, a 100 millivolt signal does not cause blanketing. Neither would a five-fold power increase in any transmitter or 2% times 100 millivolts cause blanketing. “Laboratory curves show that the average 1931-32 super¬ heterodyne receiver has selectivity such that the ratio of re¬ sponse of wanted to unwanted signals is in the order of 50,000 to 100,000, where the difference in frequency is 50 kilocycles. This is not the ultimate. Better selectivity will be available when it is needed. “I realize that there are a number of obsolete tuned radio frequency single circuit and crystal receivers in use, and of course they are not as selective as a superheterodyne receiver. If there were a general movement toward higher power, the owners of these sets might protest. In answer to that argu¬ ment, I want to read a quotation from an article in March, 1933 issue of “Electronics” written by Mr. C. W. Horn, Chief Engineer of the National Broadcasting Company: 'To refuse or make impossible improved service to a large number of listeners, because there are still a number of obsolete re¬ ceivers in use, controverts all ideas of progress. For there to be no progress until these obsolete receivers fall to pieces or die of old age is utterly unreasonable. Just as manufacturers will not build improved receivers unless there is demand for them, just so will there be no improvement in general reeep tion conditions until a situation is created whereby these few obsolete receiving sets must be replaced. A broadcasting sta¬ tion is intended to serve the public, which I interpret to mean the great majority and not a selected few. For this reason, I feel that the Federal Radio Commission could very well change its requirements, and classify areas having 1000 or more millivolts per meter as blanket areas, instead of a figure 100 millivolts as at present. Radio manufacturers will give added attention to more complete shielding and selectivity of receiving sets, so that in time even 1000 millivolts can bo exceeded. ’ “The quality of receivers has improved to a point where the old 100 millivolt blanket area no longer holds. There¬ fore, regional stations should be able to increase their power, and remain in the same location without fear of blanketing. Another cry against higher power for regionals is the asser¬ tion that heterodyned interference between regionals on the same channel would be worse. This fact was a real menace a few years ago. However, today we find transmitters main¬ taining their frequency closer than 50 cycles, thus eliminating the penetrating beat note audible on some parts of the dial. And we also find that the percentage of modulation is increased from 30 or 40% to 80 to 100%. ‘ ‘ The total effect of these two improvements is to eliminate the nuisanee type of interference and replace it with simple cross-talk. Cross-talk from channel sharing stations has never concerned us overly much. Such cross-talk that does interfere with our programs, only shows up a few hours during some evenings, and comes almost entirely from one station. Where cross talk causes difficulty, I suggest the use of reflecting sys¬ tem to concentrate the energy where it is most needed. It happens in our case that approximately 80% of our audience lies northwest of our plant. With increased power available and if it were so stipulated, we would install a reflector in such a way that the field intensity east, south and west of our transmitter remains substantially the same as it is at present, while a gain in signal intensity would be realized northwest of our plant, a place where it is most needed. Other stations on our channel are east, south, and west of our plant. In other words, the signal would be reflected away from the other stations on our channel. “It has been argued that because of the presence of the fading ring, where sky wave and ground wave meet with such intensity as to cause severe fading, increases in power, being unable to correct this, would be useless. Stations on fre¬ quencies higher than 1000 k.c. are likely to find this fading ring well within their trade area. Recent investigations have revealed that this effect can be reduced through proper antenna design at the transmitter. In addition, automatic volume con¬ trol on receiving sets has helped to still further reduce the un¬ pleasantness of fading. “Another angle to the interference problem is this: cleared channel stations have increased their power. If regionals and locals increased their power, we would find all signals arrive at the listeners receiving set at a higher level than say three years ago. What would be the effect? Just this. The lis¬ tener would decrease the sensitivity of his set. The signal in the speaker would be the same, but static and induction noises would be decreased. If that process could be carried far enough, the listener could decrease the sensitivity of his set so far that static and other noises would completely disappear. “Now to sum up: regional stations are supposed to lay down a serviceable signal over the trade area of the city in which they are located. As things are at present, most or all regional stations give only fair local coverage and fail al¬ together to give trade area coverage. A five-fold increase in the power of all regional stations would go part way toward improving this situation. The expense of this change should be well within the means of all regional stations. A general increase in station power outputs will not create an undesir . Page 169 .