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IEEE 950
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IEEE 950 1952 Edition, April 1, 1952 Recommended Practice MEASUREMENT of FIELD INTENSITY ABOVE 300 MC from RADIO-FREQUENCY INDUSTRIAL, SCIENTIFIC, and MEDICAL EQUIPMENT
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Description / Abstract:
INTRODUCTION
A. Need for Standard Method of Measuring Field Intensities at Frequencies Above 300 Megacycles.
The greatly increased use of the radio-frequency spec¬trum above 300 megacycles since World War II made necessary a re-examination of the interference problem. Not only may interference occur between equipments and services operating at these high frequencies, but also interference may be caused by equipments operating at lower frequencies with appreciable harmonic radiation above 300 megacycles.
In particular, electromagnetic radiation from radio-frequency industrial, scientific and medical equipments may cause interference to communication services above 300 megacycles. In order to eliminate objectionable interference, the Federal Communications Commission, after collaboration with manufacturers and users of such equipment, established certain regulations including limits of permissible radiation. Conformance with these regulations requires that field intensity measurements be made. At the present time, measurement standards above 300 megacycles are in the process of development. There are no commercially available field intensity meters with which measurements can be made at frequencies higher than 1000 megacycles. Until the development of standard methods and equip-ment has been completed, there is a need for a uniform practice for the measurement of field intensities above 300 megacycles.
B. FCC Regulations.
The rules adopted by the FCC relating to interference from the operation of radio-frequency industrial, scientific, and medical equipment may be found in Part 18 of the FCC Rules and Regulations, a copy of which can be obtained from the Government Printing Office, Washington, D.C. The rules relating to medical diathermy equipment and industrial heating equipment became effec-tive June 30, 1947.
A number of bands are assigned for the use of such equipment in which there is no limit to the amount of radiation permitted. For “offband” radiation, definite limits are specified for the allowable field intensity. For example, industrial heating equipment may not radiate a field having a greater intensity than 10 microvolts per meter at one mile. The limit for medical diathermy equipment radiation is IS microvolts per meter at 1000 feet. The present limits of “off-band” radiation represent a compromise between complete suppression of interference and practical equipment design. Within the compromise limits, it is hoped that the actual number of cases where objectionable interference exists will be small and that each case can be treated individually. In order to make certain that the equipment fulfills the FCC requirements, it must be certified by the manufacturer or a competent engineer. Under some conditions, type approval may be obtained for a given type of equipment. In any case, compliance with FCC requirements is based upon field intensity measurements showing that the radiation is within the required limits.
C.Committee Action. The AIEE Subcommittee on Radiation Measurements Above 300 Megacycles was organized in 1947 to study the measurement problems resulting from the FCC rules relating to the operation of radio-frequency industrial, scientific, and medical equipment. Selected parts of the material accumulated in this study are presented in this report. Information is given on methods of measurement, antenna design, and equipments used in making field intensity measurements. It is hoped that this information will serve as a guide to those making field intensity measurements above 300 megacycles.
A. Need for Standard Method of Measuring Field Intensities at Frequencies Above 300 Megacycles.
The greatly increased use of the radio-frequency spec¬trum above 300 megacycles since World War II made necessary a re-examination of the interference problem. Not only may interference occur between equipments and services operating at these high frequencies, but also interference may be caused by equipments operating at lower frequencies with appreciable harmonic radiation above 300 megacycles.
In particular, electromagnetic radiation from radio-frequency industrial, scientific and medical equipments may cause interference to communication services above 300 megacycles. In order to eliminate objectionable interference, the Federal Communications Commission, after collaboration with manufacturers and users of such equipment, established certain regulations including limits of permissible radiation. Conformance with these regulations requires that field intensity measurements be made. At the present time, measurement standards above 300 megacycles are in the process of development. There are no commercially available field intensity meters with which measurements can be made at frequencies higher than 1000 megacycles. Until the development of standard methods and equip-ment has been completed, there is a need for a uniform practice for the measurement of field intensities above 300 megacycles.
B. FCC Regulations.
The rules adopted by the FCC relating to interference from the operation of radio-frequency industrial, scientific, and medical equipment may be found in Part 18 of the FCC Rules and Regulations, a copy of which can be obtained from the Government Printing Office, Washington, D.C. The rules relating to medical diathermy equipment and industrial heating equipment became effec-tive June 30, 1947.
A number of bands are assigned for the use of such equipment in which there is no limit to the amount of radiation permitted. For “offband” radiation, definite limits are specified for the allowable field intensity. For example, industrial heating equipment may not radiate a field having a greater intensity than 10 microvolts per meter at one mile. The limit for medical diathermy equipment radiation is IS microvolts per meter at 1000 feet. The present limits of “off-band” radiation represent a compromise between complete suppression of interference and practical equipment design. Within the compromise limits, it is hoped that the actual number of cases where objectionable interference exists will be small and that each case can be treated individually. In order to make certain that the equipment fulfills the FCC requirements, it must be certified by the manufacturer or a competent engineer. Under some conditions, type approval may be obtained for a given type of equipment. In any case, compliance with FCC requirements is based upon field intensity measurements showing that the radiation is within the required limits.
C.Committee Action. The AIEE Subcommittee on Radiation Measurements Above 300 Megacycles was organized in 1947 to study the measurement problems resulting from the FCC rules relating to the operation of radio-frequency industrial, scientific, and medical equipment. Selected parts of the material accumulated in this study are presented in this report. Information is given on methods of measurement, antenna design, and equipments used in making field intensity measurements. It is hoped that this information will serve as a guide to those making field intensity measurements above 300 megacycles.