FCC METHODS OF MEASUREMENTS OF RADIO NOISE EMISSIONS
FROM INDUSTRIAL, SCIENTIFIC, AND MEDICAL EQUIPMENT

FCC METHODS OF MEASUREMENTS OF RADIO
NOISE EMISSIONS FROM INDUSTRIAL,
SCIENTIFIC, AND MEDICAL EQUIPMENT

FEBRUARY 1986                                                   FCC/OST MP-5 (1986)

Supersedes OCE Bulletins 20 and 39,
and Test Procedure No. 2


Introduction

This document sets forth uniform methods of measurements of radio noise emitted from ISM equipment, as defined in 47 CFR 18.107 of the FCC Rules.  The technical specifications for ISM equipment are contained in Part 18 of the FCC Rules.  Methods of measurements of radiated, powerline conducted radio noise, frequency and power output (when applicable) are covered herein.  Applicants for certification and parties subject to verification are encouraged to use these methods.  Testing of ISM equipment by the FCC will be conducted in accordance with these methods of measurements, to the extent possible.  This document has been separated in seven parts;

Part 1- Definitions
Part 2- General test conditions
Part 3- General tests (radiation hazard, frequency measurements)
Part 4- Radiated emission measurements for microwave ovens and medical diathermy equipment operating above 900 MHz
Part 5 -Radiated emission measurements for certified equipment
Part 6- Radiated emission measurements for verified equipment
Part 7- Conducted powerline measurements

1.0 DEFINITIONS

The definitions in Parts 2 and 18 of the FCC Rules and the following shall apply to the use of this standard.

1.1 Ambient level

The magnitude of radiated or conducted signals and noise existing at a specific test location and time.

1.2 Emission

Electromagnetic energy produced by a device which is radiated into space .or conducted along wires and is capable of being measured.

1.3 Equipment under test (EUT)

A representative piece of ISM equipment being tested or evaluated.

1.4 Ground plane

A conducting surface used to provide uniform reflection of an impinging electromagnetic wave.  Also, the common reference point for electrical potentials.

1.5 Radio noise

Electromagnetic energy in the radio frequency range that may be superimposed upon a wanted signal.

--Radiated radio noise:

Radio noise radiated into space.  Such noise may included both the radiation and induction components of the field.

--Conducted radio noise:

Radio noise propagated from the device back into the public electrical power network via the supply cord.

--Broadband radio noise:

Radio noise having a spectrum broad in width as compared to the nominal bandwidth of the measuring instrument, and whose spectral components are sufficiently close together in frequency and uniform that the measuring instrument cannot resolve them.

2.0 GENERAL TEST CONDITIONS

2.1 Test sites for certified equipment

For equipment subject to certification, an environment which assures valid, repeatable results shall be used.  A measurement is valid to the extent that it is a true representation of the characteristic being measured, and when the same measurement procedure yields repeatable results.  Measurements of radiated radio noise should be made in an open, flat area characteristic of cleared, level terrain, especially for measurements of emissions below 1 GHz.  For details on how to set up a suitable site, see FCC Bulletin OS 55, "Characteristics of Open Field Test Sites," available from the FCC Consumers Assistance Office, Washington, D.C. 20554.  Measurements made by the Commission will be performed on an open field site.  A description of the test facility used for equipment subject to certification or when required by the Commission, shall be filed, pursuant to Section 18.205 of the FCC Rules.  As an alternative, testing may be made at another location such as a laboratory, factory, anechoic chamber, etc. only if it can be shown that the results obtained at such a location are correlatable to those made in an open field site.  Sufficient tests shall be made to demonstrate that the alternative site produces results that correlate with the ones of tests made in an open field.

2.1.1 Test sites for verified equipment

Verified equipment may be tested at any location, however, the following will be observed:

--When testing is done at a location which does not have particular characteristics such as shielded walls, etc. and which yields repeatable results than the data obtained will be considered representative of how the equipment operates in general.

--When testing is done on-premises (or in-situ), both the equipment and its location are considered the EUT.  The radiated emission results, may be unique to the installation because site containment properties affect the measurements.  The conducted emanation results also may be unique to the installation.

--If a location has unique characteristics such as shielded walls, the measurements taken will be considered representative of that installation only.  For example, situations where the equipment is located in a building with metal walls or deep inside a building, with measurements taken outside that building, cannot be considered representative of how the equipment will perform at other installations where the same degree of shielding may not be present.

2.2 Measuring instrumentation

Radiated and conducted measurements shall be made with a radio noise meter that conforms with the American National Standard Specifications for Electromagnetic Interference and Field Strength Instrumentation 10 kHz to 1 GHz, ANSI C63.2-1980.  Alternatively, a spectrum analyzer may be used, provided the results obtained can be accurately reproduced with a suitable radio noise meter and that it is used, when necessary, with appropriate accessories to insure sufficient sensitivity and overload protection.  Other instruments may be used for certain restricted and specialized measurements when data so measured are correlatable to that achieved with C63.2 instrumentation.  No specific standard will be required for instrumentation used to perform measurements above 1 GHz.

Note: Accessories needed would depend upon the measurement situation and could include preamplifiers for sensitivity improvement, filters and/or attenuators for overload protection, and additional quasi-peak detection circuitry (for testing RF lighting devices).  Overload is defined as harmonic distortion, intermodulation, or gain compression of spectrum analyzer input signals.  Precautions may have to be taken to insure that the spectrum analyzer operates linearly before taking final measurements.  Consult user's manual for instructions and guidance, Application notes on the use of spectrum analyzer and other instruments are also available from several manufacturers.

2.2.1 Measuring instrument calibration

The calibration of the measuring instrumentation, including any accessories that may affect such calibration, shall be checked frequently enough to assure its accuracy.  Adjustment shall be made and correction factors applied in accordance with instructions contained in the manual for the measuring instrument.

2.2.2 Detector function selection and bandwidth

For radio noise meters or spectrum analyzers which include weighting circuits, the detector function shall be linear.  The detector function selector shall be set to average, unless otherwise specified for a given device.  For RF lighting devices, the measuring instrument shall have the detector function set to the CISPR quasi-peak function.  The 6 dB bandwidth of the measuring instrument shall not be less than:

200 Hz for measurements below 150 kHz
9 kHz for measurements from 150 kHz to 30 MHz
100 kHz for measurements from 30 to 1000 MHz
1 MHz for measurements above 1000 MHz

Post detector video filters, if used, shall be wide enough not to affect the peak detector reading.  Alternatively, field strength meters and spectrum analyzers without weighting circuits may be employed, provided measurements are made on the peak basis and recorded as observed.

Notes: 
1. The above specified bandwidths have tolerances as prescribed in ANSI standard C63.2 -1980.
2. If bandwidths greater than those specified in B2.2 are used, higher readings may result for EUT's with broadband emanations.
3. Alternative methods of reading the average will be accepted by the FCC.  Individuals should contact the FCC laboratory and discuss the appropriateness of alternate methods prior to undertaking them.

2.2.3 Units of measurements

Measurements of radiated emissions shall be reported in terms of microvolts per meter at a specified distance.  The indicated readings on the spectrum analyzer or the radio noise meter shall be converted to microvolts per meter by use of appropriate conversion factors.  Measurements of conducted emissions shall be reported in terms of microvolts.

2.2.4 Antennas

The following antennas shall be used for measuring the field strength:
--below 18 MHz shielded balanced loop
--18 to 30 MHz shielded balanced loop or calibrated tuned half-wave dipole *
--30 to 1000 MHz calibrated tuned half-wave dipole *
--above 1 GHz broadband linearly polarized horn antenna *

* Other linearly polarized antennas are acceptable provided the results obtained with such antennas are correlatable to levels obtained with a tuned dipole for measurements from 30 to 1000 MHz or a horn antenna for measurements above I GH2..

2.2.5 Antenna height variation

The measurement antenna must be varied in height above ground to obtain the maximum signal strength.

For a loop antenna.  The antenna height shall be set at around 2 meters.  Care should be taken to assure that readings are not taken in nulls.

For a dipole or equivalent antenna.  For measurement distances up to and including 10 meters, the antenna height shall be varied from 1 to 4 meters.  Beyond 10 meters, the height shall be varied from 2 to 6 meters.

For a horn or equivalent antenna.  The antenna height shall be varied from about I to 4 meters.  Antenna orientation and variations in height shall be such that readings are not taken in nulls.

These height scans apply for both horizontal and vertical polarization, except that for vertical polarization the minimum height should be increased so that the lowest point of the bottom end of the dipole (or other antenna), at any frequency, clears the site ground surface by approximately 25 centimeters.  Height variations might be constrained because of the location.

2.2.6 Antenna-to-test unit distance

Measurements shall be made at the distance at which the limits are specified, to the extent possible.  Testing may be made at closer distances, especially for equipment for which the limits are specified at distances greater than 30 meters, provided a sufficient number of measurements are made to enable plotting of the polar radiation pattern and to assure the correct determination of the major lobes.  Where conditions permit, these measurements shall be made at intervals of no more than 20 degrees in azimuth directions and at distances not exceeding the one at which the emission limit is specified.  Where possible, field strength measurements shall be made along each radial at several intervals and an average curve shall be drawn for measured field strength in uVlm versus distance in meters.  Where necessary, the average curve shall be extended to show the extrapolated field strength at the distance at which the emission limit is specified.

The Commission as an alternative shall accept measurements at a closer fixed distance, provided 1/d is used as an attenuation law factor (where d if the distance measured in appropriate units).

The measuring distance between the measuring set antenna and the BUT shall be measured from the closest point of the device or system, as determined by the boundary defined by an imaginary straight line periphery describing a simple geometric configuration enclosing the BUT system.  All intra-system cables and connecting devices shall be included within this boundary.

2.3 Frequency range to be scanned

(a) For field strength measurements:

Frequency band in which device operates (MHz) 

Range of frequency measurements

Lowest frequency Highest frequency

Below 1.705 lowest frequency generated 
30 MHz 
in the device, but not lower than 9 kHz

1.705 to 30 lowest frequency generated 
400 MHz 
in the device, but not lower than 9 kRz

30 to 500 lowest frequency generated 
tenth harmonic or 
in the device or 25 MHz, 
1000 MHz, whichever 
whichever is lower 
is higher

500 to 1000 lowest frequency generated 
tenth harmonic 
in the device or 100 MHz, whichever is lower 

above 1000 do tenth harmonic or highest detectable emission

(b) For conducted powerline measurements, the frequency range over which the limits are specified will be scanned.

Note: Automatic scan techniques are acceptable but the maximum scan speed is limited by the response time of the measuring system and (where applicable) the repetition rate of the radio noise to be measured.

2.4 Data-reporting format

The measurement results expressed in accordance with Section 2.2.3, and specific limits where applicable, shall be presented in tabular and/or graphical forms, or alternatively as recorder charts or photographs of a spectrum analyzer display, showing level vs. frequency.  Since alternate test methods are provided, test data must identify the methods used.  Instrumentation, instrument and bandwidth settings detector function, EUT arrangements, sample calculation with all conversion factors and all other pertinent details shall be included along with the measurement results.

3.0 GENERAL TESTS

3.1 Radiation hazard test

For ISM equipment operating on higher frequencies (above 900 MHz), in particular microwave ovens and medical diathermy equipment, radiation leakage should be measured in accordance with the current Bureau of Radiological Health standard, employing an electromagnetic radiation monitor.  This test is made primarily to assure that personnel will not be exposed to radiation hazard in testing the equipment.  Equipment submitted to the FCC which have radiation leakage apparently in excess of BRH limit will be reported to BRH for their evaluation.  See FCC Bulletin OST 56, "Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Radiation."

3.2 Frequency measurements

For ISM equipment designed to operate on one of the ISM frequencies, the maximum frequency deviation due to the load and normal operating conditions shall be measured and reported.  These measurements may be performed indoors.  The load effect on frequency variation is determined by finding the extreme values of frequency obtainable by adjustment of applicator spacings, external control settings, and varying loads, for each combination of applicators.

After a five minute no-load warm-up from a cold start at room temperature, determine the maximum deviations from the ISM frequency (both above and below) by making measurements with different combinations of applicators, applicator spacings, control settings, and load.

Using that combination of applicators and load spacing which produces the maximum observable power output into the load, operate the equipment from a cold start at room temperature for a sufficient amount of time to approximate normal operating conditions.  Measure the frequency at the beginning of the run and at frequent intervals until its completion.

After making the last measurement, once again adjust the controls of the equipment, vary the load, and change the applicator spacing, to find the combination that yields the worst deviation from the ISM frequency.

4.0 RADIATED EMISSIONS MEASUREMENTS FOR MICROWAVE OVENS AND MEDICAL DIATHERMY EQUIPMENT OPERATING ABOVE 900 MHz

4.1 Load for microwave ovens

For all measurements the energy developed by the oven is absorbed by a dummy load consisting of a quantity of tap water in a beaker.  A polypropylene beaker or any other low-loss material shall be used as the container.  If the oven is provided with a shelf or other utensil support, test shall be made with this support in its initial normal position.  For ovens rated at 1000 watts or Jess power output, the beaker shall contain quantities of water as listed in the following subparagraphs.  For ovens rated at more than 1000 watts output, each quantity shall be increased by 50% for each 500 watts or fraction thereof in excess of 1000 watts.  Additional beakers are used if necessary.

--Load for power output measurement: 1000 milliliters of water in the beaker located in the center of the oven.

--Load for frequency measurement: 1000 milliliters of water in the beaker located in the center of the oven.

--Load for measurement of radiation on second and third harmonic: Two loads, one of 700 and the other of 300 milliliters, of water are used.  Each load is tested both with the beaker located in the center of the oven and with it in the right front corner.

--Load for all other measurements: 700 milliliters of water, with the beaker located in the center of the oven.

4.2 Load for medical diathermy equipment

Most medical diathermy instruments are provided with more than one set of treatment applicators.  These may either be inductive or capacitive in nature; i.e., they are intended to apply electric or magnetic fields to the area of the body to be treated.  Since it not advisable to use humans as test subjects when making radiation measurements on medical diathermy equipment, artificial loads must be used.  The following loads have been used in the past, however, other loads may be used depending on the manufacturer's instructions:

--Load for inductive applicators: the load consists of a flat spiral of three turns of 1/2" wide shield braid (6" I.D./ 10" O.D.) connected to two medium-base lamp sockets in series.  The spiral is cemented between two 12" discs of insulating material for support, with the sockets attached near the center of the outer face of one disc.  In use the assembly is coupled to the applicator at such a spacing and with that combination of lamps (one or two 100 watt, 200 watt, 300 watt/ 120 volt or 100 watt/32 volt lamps) whichever produces the greatest power output into the load.  Where only one lamp is used, a plug fuse is inserted into the idle socket to complete the circuit.  For cable applicators, a wooden spider is used to form the cable into a coil of dimensions similar to the spiral in the load. . . .