TVI and the "Dallas Plan" |
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Amateur radio operators have been blamed for a lot of radio frequency interference (RFI) and television interference (TVI) over the years, with some being justified and a lot being unjustified. The surest sign that a Ham set is interfering with your entertainment box is when you actually hear voice or a series of dits and dahs. However, when the interference is a steady or waver buzzing sound or scratchy intermittent hash, chances are greater that the interference is coming from a noisy motor in a vacuum cleaner, a kitchen blender, a power tool, or an arcing power line transformer / cracked insulator. The American Radio Relay League (ARRL) has jumped through burning hoops (figuratively) to educate licensed operators on how to avoid complaints by assuring gear is functioning properly, and educating the public about the likelihood that the problems they experience are not coming from the guy down the street with big antennas in the yard but from the next-door neighbor's swimming pool filter pump. TVI and the "Dallas Plan"
One of the important subjects discussed at a recent meeting of the Radio-Television Manufacturers Association (RTMA) was the problem of amateur radio interference to television service. Such interference has been of major importance in many metropolitan areas, where crowded living conditions have placed hundreds of television receivers in close proximity to amateur stations. In some cases it has served to force the amateur off the air during television hours because of public wrath and indignation due to a misunderstanding of all the facts. The desire of the public in fringe areas for television reception has also aggravated the interference problem. When receivers are used in areas of low signal strength, even the slightest interference from amateurs or other services becomes a major problem. The Amateur Radio Activity Section, under the chairmanship of Al Kahn of Electro-Voice, discussed the correlation of the service managers' efforts and amateur activities. Both the RTMA and the FCC have set up standards for receiver performance dealing with radiation, images, etc. It should be realized that the service industry has done a tremendous job overnight in acquainting service technicians with the many problems of the complex television industry. From a total of 10,000 receivers in 1945 to the present total of over 15,000,000 sets, it has been a tremendous job to train sufficient technical help to handle the servicing of these receivers with their many attendant problems. In spite of the many excellent service manuals published by manufacturers, and the articles in various publications dealing with the problem of amateur interference, there has been little done to directly acquaint the technician with amateur interference and the remedies. Too often the technician is inclined to blame any type of interference on the neighboring amateur, especially if the amateur antenna is clearly visible. Some of this blame is due to misinformation or to inadequate training. In the majority of cases there has been no concerted effort on the part of technicians to work with the offending amateur to conduct tests designed to eliminate or reduce this interference to a negligible value. Too often the ham has been blamed for interference from neon signs, electric razors, and other assorted interferences. Part of this is due to lack of education in recognizing amateur interference, or confusing it with other types of interference. A television receiver offers its own built-in analysis method for most troubles, and the problem boils down to interpreting what you see on the screen. Too often, the general public regards the amateur as a person who pursues a hobby to the detriment of their entertainment. The many valuable services rendered by the amateur usually go unnoticed. Amateur radio is a vital part of the communications system of this country and has the full backing of government and military authorities. No other service can offer adequate emergency facilities, as attested by the sterling performance of amateurs in time of floods, hurricanes, and other disasters. The Federal Civilian Defense Administration has recognized the amateur service's value and has made provisions for stations in this service to be operated in the event of national emergency. According to the FCDA, vital services such as these are not to be disrupted during time of emergency. If the problem of amateur interference grows worse, a great many amateurs will either give up their hobby in sheer desperation or reduce their operating time to such an extent that their value will be considerably lessened. The logical solution to this problem is cooperation between the amateurs and the service groups. Almost any town of appreciable size has a service organization as well as amateur clubs. If the amateurs will contact these service organizations, and arrange to have one of their technically qualified members attend service meetings, techniques for eliminating the interference can be readily worked out. Essentially this is the method commonly known as the "Dallas Plan," and this plan has been eminently successful wherever tried. If this or some similar plan were widely used, the problem could soon be solved. To further increase the supply of adequately trained technicians, the RTMA has recently taken steps to make good technical training available. RCA Institutes is currently preparing a three-year syllabus for use in vocational high schools. This syllabus is designed to acquaint high school students with the vocational possibilities of television and will contain material on amateur radio. The RTMA is very cognizant of the interference problem and is willing to furnish manufacturers with many suggestions for improvement of receiver performance. It is very helpful to the service technician if the manufacturer's service manual contains information on the types of amateur interference and methods of recognizing them, as well as suggested cures. There is also a movement among manufacturers to include a built-in, high-pass filter in the receiver. In many cases, a high-pass filter has not eliminated interference due to improper installation, and this can be effectively controlled if the filter is installed at the time of manufacture. Onowa, Iowa recently passed an ordinance making it illegal to operate an amateur transmitter, diathermy machine, or any other device causing interference to television or radio regardless of where the fault lies. Such an ordinance is obviously invalid, but it will require a concerted effort plus a great deal of expense to make a test case of this or similar ordinance and prove its invalidity. While this ordinance, in itself, is not too important, it does indicate the type of opposition faced by amateur radio, due to misinformation. O.R.
Posted January 15, 2019 |
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By the Editor