§ 15.31   Measurement standards.

   (a) The following measurement procedures are used by the Commission to
   determine compliance with the technical requirements in this part.
   Except where noted, copies of these procedures are available from the
   Commission's current duplicating contractor whose name and address are
   available from the Commission's Consumer and Governmental Affairs
   Bureau at 1-888-CALL-FCC (1-888-225-5322).

   (1) FCC/OET MP-2: Measurement of UHF Noise Figures of TV Receivers.

   (2) Unlicensed Personal Communications Service (UPCS) devices are to be
   measured for compliance using ANSI C63.17-2013: “American National
   Standard Methods of Measurement of the Electromagnetic and Operational
   Compatibility of Unlicensed Personal Communications Services (UPCS)
   Devices” (incorporated by reference, see § 15.38).

   (3) Other intentional radiators are to be measured for compliance using
   the following procedure: ANSI C63.10-2013 (incorporated by reference,
   see § 15.38).

   (4) Unintentional radiators are to be measured for compliance using the
   following procedure excluding clauses 4.5.3, 4.6, 6.2.13, 8.2.2, 9, and
   13: ANSI C63.4-2014 (incorporated by reference, see § 15.38).

   (b) All parties making compliance measurements on equipment subject to
   the requirements of this part are urged to use these measurement
   procedures. Any party using other procedures should ensure that such
   other procedures can be relied on to produce measurement results
   compatible with the FCC measurement procedures. The description of the
   measurement procedure used in testing the equipment for compliance and
   a list of the test equipment actually employed shall be made part of an
   application for certification or included with the data required to be
   retained by the party responsible for devices authorized pursuant to a
   Declaration of Conformity or devices subject to verification.

   (c) Except as otherwise indicated in § 15.256, for swept frequency
   equipment, measurements shall be made with the frequency sweep stopped
   at those frequencies chosen for the measurements to be reported.

   (d) Field strength measurements shall be made, to the extent possible,
   on an open field site. Test sites other than open field sites may be
   employed if they are properly calibrated so that the measurement
   results correspond to what would be obtained from an open field site.
   In the case of equipment for which measurements can be performed only
   at the installation site, such as perimeter protection systems, carrier
   current systems, and systems employing a “leaky” coaxial cable as an
   antenna, measurements for verification or for obtaining a grant of
   equipment authorization shall be performed at a minimum of three
   installations that can be demonstrated to be representative of typical
   installation sites.

   (e) For intentional radiators, measurements of the variation of the
   input power or the radiated signal level of the fundamental frequency
   component of the emission, as appropriate, shall be performed with the
   supply voltage varied between 85% and 115% of the nominal rated supply
   voltage. For battery operated equipment, the equipment tests shall be
   performed using a new battery.

   (f) To the extent practicable, the device under test shall be measured
   at the distance specified in the appropriate rule section. The distance
   specified corresponds to the horizontal distance between the
   measurement antenna and the closest point of the equipment under test,
   support equipment or interconnecting cables as determined by the
   boundary defined by an imaginary straight line periphery describing a
   simple geometric configuration enclosing the system containing the
   equipment under test. The equipment under test, support equipment and
   any interconnecting cables shall be included within this boundary.

   (1) At frequencies at or above 30 MHz, measurements may be performed at
   a distance other than what is specified provided: measurements are not
   made in the near field except where it can be shown that near field
   measurements are appropriate due to the characteristics of the device;
   and it can be demonstrated that the signal levels needed to be measured
   at the distance employed can be detected by the measurement equipment.
   Measurements shall not be performed at a distance greater than 30
   meters unless it can be further demonstrated that measurements at a
   distance of 30 meters or less are impractical. When performing
   measurements at a distance other than that specified, the results shall
   be extrapolated to the specified distance using an extrapolation factor
   of 20 dB/decade (inverse linear-distance for field strength
   measurements; inverse-linear-distance-squared for power density
   measurements).

   (2) At frequencies below 30 MHz, measurements may be performed at a
   distance closer than that specified in the regulations; however, an
   attempt should be made to avoid making measurements in the near field.
   Pending the development of an appropriate measurement procedure for
   measurements performed below 30 MHz, when performing measurements at a
   closer distance than specified, the results shall be extrapolated to
   the specified distance by either making measurements at a minimum of
   two distances on at least one radial to determine the proper
   extrapolation factor or by using the square of an inverse linear
   distance extrapolation factor (40 dB/decade). This paragraph (f) shall
   not apply to Access BPL devices operating below 30 MHz.

   (3) For Access BPL devices operating below 30 MHz, measurements shall
   be performed at the 30-meter reference distance specified in the
   regulations whenever possible. Measurements may be performed at a
   distance closer than that specified in the regulations if circumstances
   such as high ambient noise levels or geographic limitations are
   present. When performing measurements at a distance which is closer
   than specified, the field strength results shall be extrapolated to the
   specified distance by using the square of an inverse linear distance
   extrapolation factor (i.e., 40 dB/decade) in conjunction with the
   slant-range distance defined in § 15.3(hh) of this part. As an
   alternative, a site-specific extrapolation factor derived from a
   straight line best fit of measurements of field strength in dBµV/m vs.
   logarithmic distance in meters for each carrier frequency, as
   determined by a linear least squares regression calculation from
   measurements for at least four distances from the power line, may be
   used. Compliance measurements for Access BPL and the use of
   site-specific extrapolation factors shall be made in accordance with
   the Measurement Guidelines for Access BPL systems specified by the
   Commission. Site-specific determination of the distance extrapolation
   factor shall not be used at locations where a ground conductor is
   present within 30 meters if the Access BPL signals are on the
   neutral/grounded line of a power system.

   (4) The applicant for a grant of certification shall specify the
   extrapolation method used in the application filed with the Commission.
   For equipment subject to Declaration of Conformity or verification,
   this information shall be retained with the measurement data.

   (5) When measurement distances of 30 meters or less are specified in
   the regulations, the Commission will test the equipment at the distance
   specified unless measurement at that distance results in measurements
   being performed in the near field. When measurement distances of
   greater than 30 meters are specified in the regulations, the Commission
   will test the equipment at a closer distance, usually 30 meters,
   extrapolating the measured field strength to the specified distance
   using the methods shown in this section.

   (6) Measurements shall be performed at a sufficient number of radials
   around the equipment under test to determine the radial at which the
   field strength values of the radiated emissions are maximized. The
   maximum field strength at the frequency being measured shall be
   reported in the equipment authorization report. This paragraph shall
   not apply to Access BPL equipment on overhead medium voltage lines. In
   lieu thereof, the measurement guidelines established by the Commission
   for Access BPL shall be followed.

   (g) Equipment under test shall be positioned and adjusted, using those
   controls that are readily accessible to or are intended to be
   accessible to the consumer, in such a manner as to maximize the level
   of the emissions. For those devices to which wire leads may be attached
   by the operator, tests shall be performed with wire leads attached. The
   wire leads shall be of the length to be used with the equipment if that
   length is known. Otherwise, wire leads one meter in length shall be
   attached to the equipment. Longer wire leads may be employed if
   necessary to interconnect to associated peripherals.

   (h) For a composite system that incorporates devices contained either
   in a single enclosure or in separate enclosures connected by wire or
   cable, testing for compliance with the standards in this part shall be
   performed with all of the devices in the system functioning. If an
   intentional radiator incorporates more than one antenna or other
   radiating source and these radiating sources are designed to emit at
   the same time, measurements of conducted and radiated emissions shall
   be performed with all radiating sources that are to be employed
   emitting. A device which incorporates a carrier current system shall be
   tested as if the carrier current system were incorporated in a separate
   device; that is, the device shall be tested for compliance with
   whatever rules would apply to the device were the carrier current
   system not incorporated, and the carrier current system shall be tested
   for compliance with the rules applicable to carrier current systems.

   (i) If the device under test provides for the connection of external
   accessories, including external electrical input signals, the device
   shall be tested with the accessories attached. The device under test
   shall be fully exercised with these external accessories. The emission
   tests shall be performed with the device and accessories configured in
   a manner that tends to produce maximized emissions within the range of
   variations that can be expected under normal operating conditions. In
   the case of multiple accessory external ports, an external accessory
   shall be connected to one of each type of port. Only one test using
   peripherals or external accessories that are representative of the
   devices that will be employed with the equipment under test is
   required. All possible equipment combinations do not need to be tested.
   The accessories or peripherals connected to the device being tested
   shall be unmodified, commercially available equipment.

   (j) If the equipment under test consists of a central control unit and
   an external or internal accessory(ies) (peripheral) and the party
   verifying the equipment or applying for a grant of equipment
   authorization manufactures or assembles the central control unit and at
   least one of the accessory devices that can be used with that control
   unit, testing of the control unit and/or the accessory(ies) must be
   performed using the devices manufactured or assembled by that party, in
   addition to any other needed devices which the party does not
   manufacture or assemble. If the party verifying the equipment or
   applying for a grant of equipment authorization does not manufacture or
   assemble the central control unit and at least one of the accessory
   devices that can be used with that control unit or the party can
   demonstrate that the central control unit or accessory(ies) normally
   would be marketed or used with equipment from a different entity,
   testing of the central control unit and/or the accessory(ies) must be
   performed using the specific combination of equipment which is intended
   to be marketed or used together. Only one test using peripherals or
   accessories that are representatve of the devices that will be employed
   with the equipment under test is required. All possible equipment
   combinations are not required to be tested. The accessories or
   peripherals connected to the device being tested shall be unmodified,
   commercially available equipment.

   (k) A composite system is a system that incorporates different devices
   contained either in a single enclosure or in separate enclosures
   connected by wire or cable. If the individual devices in a composite
   system are subject to different technical standards, each such device
   must comply with its specific standards. In no event may the measured
   emissions of the composite system exceed the highest level permitted
   for an individual component. For digital devices which consist of a
   combination of Class A and Class B devices, the total combination of
   which results in a Class A digital device, it is only necessary to
   demonstrate that the equipment combination complies with the limits for
   a Class A device. This equipment combination may not be employed for
   obtaining a grant of equipment authorization or verifying a Class B
   digital device. However, if the digital device combination consists of
   a Class B central control unit, e.g., a personal computer, and a Class
   A internal peripheral(s), it must be demonstrated that the Class B
   central control unit continues to comply with the limits for a Class B
   digital device with the Class A internal peripheral(s) installed but
   not active.

   (l) Measurements of radio frequency emissions conducted to the public
   utility power lines shall be performed using a 50 ohm/50 uH
   line-impedance stabilization network (LISN).

   (m) Measurements on intentional radiators or receivers, other than TV
   broadcast receivers, shall be performed and, if required, reported for
   each band in which the device can be operated with the device operating
   at the number of frequencies in each band specified in the following
   table:
   Frequency range over which device operates Number of frequencies
   Location in the range of operation
   1 MHz or less 1 Middle.
   1 to 10 MHz 2 1 near top and 1 near bottom.
   More than 10 MHz 3 1 near top, 1 near middle and 1 near bottom.

   (n) Measurements on TV broadcast receivers shall be performed with the
   receiver tuned to each VHF frequency and also shall include the
   following oscillator frequencies: 520, 550, 600, 650, 700, 750, 800,
   850, 900 and 931 MHz. If measurements cannot be made on one or more of
   the latter UHF frequencies because of the presence of signals from
   licensed radio stations or for other reasons to be detailed in the
   measurement report, measurements shall be made with the receiver
   oscillator at a nearby frequency. If the receiver is not capable of
   receiving channels above 806 MHz, the measurements employing the
   oscillator frequencies 900 and 931 MHz may be omitted.

   (o) The amplitude of spurious emissions from intentional radiators and
   emissions from unintentional radiators which are attenuated more than
   20 dB below the permissible value need not be reported unless
   specifically required elsewhere in this part.

   (p) In those cases where the provisions in this section conflict with
   the measurement procedures in paragraph (a) of this section and the
   procedures were implemented after June 23, 1989, the provisions
   contained in the measurement procedures shall take precedence.

   (q) As an alternative to § 15.256, a level probing radar (LPR) may be
   certified as an intentional radiator by showing compliance with the
   general provisions for operation under part 15 subpart C of this
   chapter, provided that the device is tested in accordance with the
   provisions in either paragraphs (q)(1) or (2) of this section.
   Compliance with the general provisions for an intentional radiator may
   require compliance with other rules in this part, e.g., § § 15.5, 15.31,
   and 15.35, etc., when referenced.

   (1) An LPR device intended for installation inside metal and concrete
   enclosures may show compliance for radiated emissions when measured
   outside a representative enclosure with the LPR installed inside, in
   accordance with the measurement guidelines established by the
   Commission for these devices. LPR devices operating inside these types
   of enclosures shall ensure that the enclosure is closed when the radar
   device is operating. Care shall be taken to ensure that gaskets,
   flanges, and other openings are sealed to eliminate signal leakage
   outside of the structure. The responsible party shall take reasonable
   steps to ensure that LPR devices intended for use in these types of
   enclosures shall not be installed in open-air environments or inside
   enclosures with lower radio-frequency attenuating characteristics
   (e.g., fiberglass, plastic, etc.). An LPR device approved under this
   subsection may only be operated in the type of enclosure for which it
   was approved.

   (2) Except as provided in paragraph (q)(1) of this section, an LPR
   device shall be placed in testing positions that ensure the field
   strength values of the radiated emissions are maximized, including in
   the main beam of the LPR antenna.

   [ 54 FR 17714 , Apr. 25, 1989, as amended at  56 FR 13083 , Mar. 29, 1991;
    57 FR 24990 , June 12, 1992;  57 FR 33448 , July 29, 1992;  58 FR 37430 ,
   July 12, 1993;  58 FR 51249 , Oct. 1, 1993;  61 FR 14502 , Apr. 2, 1996;  62 FR 41881 , Aug. 4, 1997;  62 FR 45333 , Aug. 27, 1997;  63 FR 36602 , July
   7, 1998;  63 FR 42278 , Aug. 7, 1998;  65 FR 58466 , Sept. 29, 2000;  68 FR 68545 , Dec. 9, 2003;  69 FR 54034 , Sept. 7, 2004;  70 FR 1373 , Jan. 7,
   2005;  76 FR 71908 , Nov. 21, 2011;  77 FR 4913 , Feb. 1, 2012;  77 FR 43013 , July 23, 2012;  79 FR 12677 , Mar. 6, 2014;  80 FR 2838 , Jan. 21,
   2015;  80 FR 33447 , June 12, 2015]

   return arrow Back to Top