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Inside FCC Part 15 and Canada's Corresponding StandardsBy Roland W. Gubisch ITS Intertek Testing Services (Boxborough, MA) In order to prevent interference to the reception of radio and TV broadcasts, and to protect other sensitive radio services such as aircraft navigation and emergency beacons, the FCC in 1975 established Part 15. These rules are directed at equipment that does not deliberately generate RF energy, as well as at low-power radio transmitters that do not require individual licensing. Part 15 affects a larger variety of electronic devices than does any other FCC regulation, imposing RF emissions limits on TV sets and radios, personal computers and peripherals, remote controls for home alarms and auto accessories, paging receivers, commercial networking systems, cable TV boxes, and electronic toys. Other parts of Chapter 47 of the Code of Federal Regulations (47 CFR) regulate high-volume products such as cellular telephones (Part 22) and high-power walkie-talkies (Part 90), but none covers such a diverse product mix as Part 15. Two other parts of CFR 47 also address license-free RF generators: Part 18 for so-called Industrial, Scientific, and Medical (ISM) devices, and Part 95 for Personal Radio Services. ISM equipment uses RF energy to perform work; typical products covered by Part 18 include microwave ovens and ultrasonic humidifiers. Part 18 is narrower in scope than either the international standard for ISM devices, CISPR 11, or its European Union equivalent, EN 55011. Products approved under Part 95 include Citizens Band (CB) radio transmitters at 27 MHz (note, however, that CB receivers fall under Part 15), radio-controlled (R/C) toys, also at 27 MHz, and the new Family Radio Service, added in 1996, which provides a voice-only walkie-talkie function of moderate power and range, operating at 463/468 MHz. Over the years, as new electronic devices were introduced into the marketplace, the FCC simply added one subpart after another to its Part 15 rules to control the potential interference from the new product type. Thus handled were Auditory Assistance Devices (Subpart G), TV Interface Devices (Subpart H), and personal computers and peripherals (Subpart J). In 1989 the rules were rewritten, largely to consolidate all the added subparts. The "new" Part 15 rules became effective in 1992 and contained only three subparts: A, B, and C. The revision also changed the FCC compliance statement and added a few ISM frequency bands for low-power communications. Since 1992, two new subparts have been incorporated into Part 15: Subpart D was added in 1993 (for Unlicensed Personal Communications Service, or UPCS, devices), and Subpart E in 1996 (for Unlicensed National Information Infrastructure, or U-NII, devices). All of these regulatory subparts will be described later in this article. In 1998, the FCC streamlined its rules by eliminating the categories of notification and type acceptance (FCC 98–58). It folded these categories into Declaration of Conformity and Certification procedures. Many parts of CFR 47 were affected, including Part 15.
The development of Canadian regulations to parallel U.S. Part 15 began in 1988, with Canada's adoption of changes to its radio regulations for personal computers and peripherals; rules regarding ISM devices were by then already on the books. At the present time, there are several different Canadian statutes covering the same territory as Part 15 (see Table I). The technical requirements are very closely harmonized with U.S. requirements, but in some cases separate label statements or application procedures are mandated for each country. The Technical Requirements of Part 15 Subpart A: General (15.1–15.37) Contrary to its "General" title, Subpart A in fact contains a great deal of very specific information that must be observed to ensure compliance, under the following key headings: scope of the rules and legal implications (15.1), definitions (15.3), prohibition against eavesdropping through the use of a Part 15 device (15.9), labeling (15.19), information to the user (15.21), measurement standards (15.31), RF detectors to be used (15.35), and frequency range to be measured (15.33). It further stipulates that scanning receivers must not be capable of receiving cellular transmissions (15.37). T he scope and legal provisions specify that Part 15 "regulates intentional, unintentional and incidental radiators operated without an individual license. Operation or marketing of intentional or unintentional radiators without complying with Part 15 technical and administrative rules is a violation of the Communications Act of 1934." The definitions describe some of the terms used in Part 15. A sampling follows:
There are many more definitions in 15.3, but those reproduced above are the most commonly used. Part 15 contains some broad provisions in Sections 15.5, 15.13, and 15.15 that require the observance of good manufacturing practices in order to reduce RF emissions from incidental, intentional, and unintentional radiators, regardless of which technical rules apply. These provisions also empower the FCC to terminate the operation of any RF device found to cause interference—even if the device is exempted from any technical compliance requirements—until the condition has been corrected. Hence, it is good practice to verify some degree of emissions compliance even for exempted equipment. The issue of susceptibility of equipment is addressed in 15.17, but the approach adopted here is very different from that taken by the EU's EMC Directive. In this section of Part 15, parties responsible for equipment compliance are advised to consider existing sources of high RF energy and to design their equipment in such a way as to increase its immunity to that energy. Typical RF sources cited include broadcast radio/TV stations, amateur radio transmitters, and land mobile stations. The responsible party or manufacturer is not required to ensure a specific level of electromagnetic immunity for the equipment. Labeling Requirements Incorrect or absent FCC compliance labels are a prime trigger for enforcement activities. The correct compliance label varies according to product type and authorization (approval) method, as follows: Declaration of Conformity (DoC) labels apply to Class B personal computers and PC peripherals, and to PC power supplies and CPU boards used with Class B PCs. Two different types of labels are used, one for PCs that have been tested while fully assembled (and for separately tested CPU boards and power supplies), shown in Figure 1, and the other for PCs assembled from authorized components without testing, Figure 2. To use the "tested" DoC label, the responsible party must have a test report from a duly accredited test laboratory (NVLAP or A2LA), which must be located in a country recognized by the FCC for this purpose.
Certification labels apply to the same products and modules as the DoC label but may be used only where the authorization has involved an application to the FCC and subsequent approval. These labels also apply to low-power transmitters, specific receivers (CB, scanning, and superregenerative), and TV interface devices. They carry no graphics at all, just words and the FCC ID number, which the commission uses to track the responsible party. The ID number consists of a three-character Grantee Code (assigned by the FCC upon request) and up to 14 additional alphanumeric characters of the applicant's choosing. More details on the FCC ID number may be found in Section 2.926 of FCC Part 2. Figures 3 and 4 illustrate the required notice that must be included in all certification labels.
Verification labels apply to all of the other devices for which no filing with the FCC is required. There are two types of verification labels, one to be used for stand-alone cable input selector switches (shown in Figure 5), and one for all of the other verified devices (Figure 6). The latter label is identical to the certification label shown in Figure 4, with the omission of the FCC ID number.
Note that none of these labels refers to either Class A or Class B emissions, nor to any specific subpart of Part 15. The detailed documentation rules for Declarations of Conformity (2.1071), Certifications (2.1031), and Verifications (2.951) are contained in Part 2 of the FCC Rules. It is important to note, too, that the appropriate authorizations must be obtained prior to any sale, and that products intended for the general public may not be offered for sale or lease until the appropriate authorizations are received (2.803). In addition to providing the correct labels, the manufacturer of or party responsible for intentional or unintentional radiators must also supply appropriate Information to the User (15.21), generally in the instruction manual. This information must caution the user that any changes or modifications not expressly approved by the responsible party could void the user's authority to operate the equipment. Specifics on what must be included in the Information to the User are given for Class A and Class B digital devices in Subpart B. At present, a single measurement standard (15.31) governs most of the devices in Part 15: ANSI C63.4-1992, "Methods of Measurement of Radio-Noise Emissions from Low-Voltage Electrical and Electronic Equipment in the Range of 9 kHz to 40 GHz." Designed to apply to both unintentional radiators (e.g., PCs, receivers, TV interface devices, etc.) and low-power transmitters, this standard includes the performance criteria for radiated-emissions measurement sites (site attenuation) imposed by the FCC and accrediting authorities, and provides detailed setup diagrams and step-by-step test procedures for both radiated- and conducted-emissions measurements (Figures 7–9). Because the Amendment 2:1995 to CISPR 22:1993, combined with CISPR 22:1993 itself, is well harmonized with the details of ANSI C63.4-1992, it is possible to follow just one measurement procedure for Information Technology Equipment (ITE) in the United States, in the EU, and internationally. Most of the measurements required by the FCC in Part 15 are either radiated (i.e., measured with an antenna) or conducted (connected directly to the mains cord or an antenna terminal). Another measurement standard, ANSI C63.17 (1998) contains the additional measurement procedures required for Unlicensed Personal Communications Services (UPCS) devices under Part 15 Subpart D. UPCS transmitters must operate with a complex communication protocol to avoid interference and guarantee fair access to the spectrum. Part 15 permits radiated-emissions measurements
to be made at distances other than those specified
in the rules, as measured from the antenna
to the nearest point of the equipment under
test (EUT). (Note, however, that there are
restrictions on measurement distances in both
CISPR and EU standards.) In general it is
not necessary to exceed a 30-m distance. The
smallest distance d is limited by the need
to remain outside of the "near field," usually
defined in terms of the wavelength Scaling of measured values or limits is allowed when measurements are made at distances other than those specified in the Part 15 rules. The extrapolation factor is 20 dB/decade for frequencies between 30 MHz and 40 GHz, and 40 dB/decade below 30 MHz and in the near field above 40 GHz. This means that for a distance change of 10:1 (a decade), the limit, or measured value, may be recalculated by adding (moving closer) or subtracting (moving away) 20 dB or 40 dB, respectively. For distance changes of less than a decade, the extrapolation value Ex may be calculated for the distances d1 and d2 from a) Ex = 20 log10(d1/d2) for 20 dB/decade, and b) Ex = 40 log10(d1/d2) for 40 dB/decade. It is also possible to make radiated-emissions measurements at two different distances and extrapolate to a third distance. From equation a) above, the extrapolation factors for distance changes between 3 and 10 meters, and between 10 and 30 meters, are 3 These pairs of results are often rounded to ±10 dB each, as the measurement uncertainty for radiated emissions is typically ±3 dB or greater. Section 15.31 on measurement standards also indicates how composite systems are to be tested and specifies the correct setups for devices that support accessories. Composite systems are those that incorporate two or more discrete devices in a single enclosure, or in separate enclosures connected by wires or cables. These requirements, which are amplified in Subpart B for personal computers and peripherals, are summarized here:
Also provided in this section are the test-frequency requirements for intentional radiators or receivers (not including TV broadcast receivers) that can operate on or tune to more than one frequency. If the operating band is 1 MHz or less, testing is to be performed at only one frequency, in the middle of the band. From 1 to 10 MHz, testing is required at two frequencies, one near the top and one near the bottom of the band. If the device operates over more than 10 MHz, testing must include three frequencies, one each near the top, middle, and bottom of the band. Test procedures for CPU boards and PC power supplies, pursuant to authorization either by certification or by Declaration of Conformity, are contained in Section 15.32. These procedures are not found in ANSI C63.4-1992. For both CPU boards and PC power supplies, the typical host enclosure shall be fully populated with these modules, plus peripherals and subassemblies, so as to make up a complete personal computer system. Very briefly, the procedures are as follows:
Conducted emissions are measured with the enclosure fully assembled. The frequency range of radiated measurements is defined in Section 15.33. This range differs for intentional radiators and unintentional radiators both with and without digital devices, as shown in Table II.
Measurement detector functions are specified in Section 15.35 of Part 15. These are selected such that measurements of emissions will correspond to the way a receiver operating in the given frequency band would respond to actual interference. Below 1000 MHz, the measurement detector should be either quasi-peak, in accordance with CISPR 16, or, alternatively, peak. The time constants of the quasi-peak detector mimic how a radio or TV receiver would respond to radio noise. Spectrum analyzers, which provide rapid assessment of emissions using the peak detector function (responding instantaneously to radio noise), are typically available with quasi-peak options. Measurement receivers are generally more expensive than spectrum analyzers, but they offer very accurate quasi-peak detector functions. For radiated-emissions measurements above 1000 MHz, Part 15 rules call for an average detector, to provide a long-term averaging that will not respond to any rapid changes. In certain cases, the rules also require the use of an average detector below 1000 MHz, as for example with pulse-modulated remote-control transmitters. In such instances, a peak limit is also specified, with the peak value not to exceed the average one by more than 20 dB. With pulse modulation, averaging may alternatively be accomplished by capturing the transmitted waveform with a peak detector and calculating the average value manually. Subpart B: Unintentional Radiators (15.101–15.121) The category of "unintentional radiators" includes a wide variety of devices that contain clocks or oscillators and logic circuitry but that do not deliberately generate RF emissions. Among such unintentional radiators are personal computers, peripherals, receivers, radios and TV sets, and cable TV home terminals. Because the threat of interference can vary greatly from one type of device to another, the FCC has in Section 15.101 established a number of different authorization pathways for unintentional radiators, as summarized in Table III.
A number of product types are exempt from having to comply with all technical requirements of Part 15 except for the general rule that they may not cause interference. Section 15.103 exempts those digital devices that:
The final exempt class of device is:
Section 15.105 details very specific instructions to the user that must be furnished in instruction manuals for Class A and Class B digital devices. The Class A statement cautions that operation of the device in a residential area is likely to cause harmful interference; the Class B statement offers several suggestions for minimizing interference to radio or TV receivers, including reorienting the receiving antenna and moving the Class B device farther away from the receiver. Two levels of radiated and conducted emissions limits for unintentional radiators are specified in Subpart B, as they pertain to 1) Class A digital devices (the higher, or less strict, limits) and 2) everything else (the lower, or stricter, limits). Products such as receivers and TV interface devices, because they are not Class A digital devices, must meet the lower Class B limits. In 1993, the FCC harmonized its rules regarding the authorization of unintentional radiators with the international emissions standard CISPR 22. As a result, vendors may now use either FCC Subpart B or CISPR 22 limits for the purposes of verification, certification, notification, or preparation of a Declaration of Conformity. This flexibility is subject to a few restrictions, as follows:
FCC conducted-emissions limits are specified in Section 15.107 (see Table IV). The conducted limits of CISPR 22 are not listed in Part 15, but they are shown in Table V for comparison.
Note that the FCC gives the limit values in µV. CISPR limits are given in dBµV. To convert FCC limits to the logarithmic format, one uses the formula Value in dBµV = 20 log10(Value in µV/1µV) There are special limits for carrier current systems that operate by using the mains wiring either as intercom wiring or as an antenna. Conducted emissions are measured with a Line
Impedance Stabilization Network (LISN), also
known as an Artificial Mains Network (AMN).
This network is constructed in such a way as
to provide a stable impedance to the RF energy
that propagates down the mains wiring and to
match the typical RF impedance of the mains
wiring (50 Note that the CISPR 22 conducted limits require compliance with both quasi-peak and average detectors, a stipulation that effectively constrains both narrow-band and broadband emissions. A provision in FCC 15.107(d) serves much the same purpose in stating that if a quasi-peak measurement exceeds the same emission measured with an average detector by 6 dB or more, the emission may be regarded as broadband, and the quasi-peak reading may be reduced by 13 dB for comparison with the limit. FCC radiated-emissions limits are given in Section 15.109. Once again, the corresponding CISPR limit values are not published in Part 15, but are given here (see Table VI). Comparing the two sets of values requires some calculation, not only because the FCC limits are given in µV/m and the CISPR limits in dBµV/m, but also because the required measurement distances differ. The FCC uses 10 meters for Class A and 3 meters for Class B; CISPR 22:1985, cited in Part 15, specifies 30 meters for Class A and 10 meters for Class B (the current version, CISPR 22:1997, uses 10 meters for both Class A and Class B). Table VI assumes a measurement distance of 10 m for all limits, using the factor 20 dB/decade where necessary.
Requirements for TV interface devices are laid out in Section 15.115. In addition to the emissions limits described above, these devices are subject to limits on RF output signal levels. The precise values of these limits will depend on the impedance of the terminal being tested. If the device contains a transfer switch for use with a cable system or a master antenna, switch isolation must be measured; isolation requirements range from 55 dB to 80 dB, depending on frequency range. Cable-ready consumer electronics, covered in Section 15.118, must also meet radiated-emissions limits, using a special test setup. They must receive all NTSC channels from 54 to 804 MHz and must additionally meet specified limits for adjacent-channel interference, image-channel interference, direct pickup interference, tuner overload, and cable-input conducted emissions. Broadcast TV receivers (addressed in Section 15.117) are also subject to Subpart B emissions limits. The FCC requires similar visibility and access to both UHF and VHF channels, as well as closed-caption decoders for all TV sets with screens larger than 13 inches (measured diagonally). Subpart C: Intentional Radiators (15.201–5.255) The various types of intentional radiators covered by Subpart C include cable locating equipment, cordless telephones, remote- control and alarm transmitters, field-disturbance sensors for opening doors, and spread-spectrum systems for wideband data transmission. Here there is no lower limit to operating power below which FCC authorization is not required. Most devices require certification, though verification is permitted for tunnel radio systems (Section 15.211), cable locating equipment (15.213), and low-power AM transmitters in the 525–1705 kHz band using either carrier current or "leaky" coaxial cable transmission (15.221). FCC approval is not required for home-built devices, but such devices must not cause interference. Intentional radiators governed by Subpart C must either have a permanently attached antenna or provide a unique coupler to prevent the use of unauthorized antennas (Section 15.203). Transmitters operating below 1.705 MHz and carrier-current systems are exempt from this requirement, as are devices installed by professionals. Selection of an appropriate frequency and operating power to comply with the rules in Subpart C requires the observation of several parameters, as follows:
Section 15.207 stipulates that conducted emissions from intentional radiators must meet the limits imposed for Class B digital devices, unless the transmitter is a carrier-current system that deliberately uses RF energy conducted into the mains wiring. In that case, special limits apply; if the device operates at 535–1705 kHz for detection by a standard broadcast receiver, there are no conducted limits. The rules for operation of radio transmitters under the specific sections of Subpart C are for the most part very detailed regarding fundamental field strength, power and/or power density, frequency accuracy, and permitted harmonic and spurious emissions. In some instances, antenna gain enters into the calculation of maximum permitted power. The equipment designer should consult the full text of the Part 15 rules for guidance. Subpart D: Unlicensed Personal Communications Services (15.301–15.323) The term personal communication services (PCS) describes a series of new wireless utilities that in many cases have yet to be deployed. Some of the capabilities foreseen include new digital cellular systems, two-way paging, and portable broadband data links. Spectrum in the 2 GHz band has been auctioned off for use in licensed PCS services, and an elaborate system of compensation and coordination has been put in place to compensate the prior spectrum users that are being displaced. Three different types of PCS services have been established in the FCC rules. Note, in particular, how the unlicensed PCS or UPCS band is sandwiched into the broadband licensed spectrum:
Because prior users have not yet fully vacated the UPCS spectrum, the FCC currently requires coordination and management (Section 15.307) of new users, and has set up UTAM, Inc., to oversee the process. Because this portion of the spectrum is expected to be quite popular, Subpart D prescribes a detailed spectrum etiquette to avoid interference and ensure fair access to the available bandwidth.
Owing to the present need for coordination, UPCS transmitters require an additional label statement (Section 15.311) over and above that specified in Section 15.19 (Figure 10). UPCS transmitters are subject to the same conducted-emissions limits and antenna-connection constraints imposed for intentional radiators under Subpart C. The technical requirements (Section 15.319) common to all UPCS transmitters are as follows:
In addition, there are two different spectrum etiquette protocols that apply here. Asynchronous transmission (i.e., transmission at irregular intervals, as seen with Ethernet systems) pertains to devices using the 1910–1920 MHz subband and 2390–2400 MHz. Isochronous transmission (i.e., transmission at regular intervals) is required in the 1920–1930 MHz subband. Details are provided in Section 15.321 for asynchronous devices and in Section 15.323 for isochronous equipment. Measurement standards for these transmission models have been published under ANSI C63.18 (1998). Note that investigation of Unlicensed Personal Communications Services devices is required under the FCC's Guidelines for Evaluating the Environmental Effects of Radiofrequency Radiation. Subpart E: Unlicensed National Information Infrastructure Devices (15.401-15.407) Additional spectrum has been made available around 5 GHz for unlicensed transmitters in wideband, high-data-rate digital communications for both fixed and mobile uses by individuals, businesses, and institutions such as hospitals, schools, and libraries. Wireless Internet access is one example of a potential Unlicensed National Information Infrastructure (U-NII) application.
U-NII devices are subject to the same conducted-emissions and restricted-band limits as other intentional radiators, as well as the same antenna constraints. Peak transmit power and peak spectral density (Section 15.405) are a function of the operating band, as tabulated in Table IX. In each band, peak transmit power and power density must be reduced by the value of antenna gain in dB for any antenna gain greater than 6 dBi. Devices that operate in the 5.15-5.25 GHz band are restricted to indoor operation in order to avoid interference with mobile satellite services. Here again, investigation of U-NII devices is required under the FCC's Guidelines for Evaluating the Environmental Effects of Radiofrequency Radiation. Summary: Part 15 The foregoing represents only a brief review of the key provisions of Part 15, with comments added. Those who intend to design or test devices in accordance with Part 15 should consult the full published version, since many details have been omitted here for the sake of brevity. Readers should be aware that some Part 15 intentional radiators—especially those operating at very high frequencies or powers—are subject to RF radiation exposure evaluation under Section 2.1091 and 2.1093 of the FCC rules. The technical standards for this evaluation are contained in the OET Bulletin 65, available from the FCC Web site at http://www.fcc.gov. A comparable Canadian standard, RSS-102, is in preparation. The Requirements of Industry Canada The structure of spectrum management and interference prevention in Canada is somewhat different from that imposed in the United States, though a good many of the technical regulations are either similar or identical. Industry Canada, the administrative authority for both radio and wire line telecom use, has only one common filing procedure, which is termed "certification." Where certification is not required, products are either unregulated or subject to verification by the manufacturer or importer. Unintentional Radiators Verification is required for products falling within the scope of Canada's Interference-Causing Equipment Standards (ICESs):
For each of these standards, a product's manufacturer or importer is required to retain for at least five years a record of all compliance measurements performed and to make this record available to the government upon request. A written notice indicating compliance must accompany each product—preferably as a label on the product itself, but alternatively as a statement included in the user's manual. Digital-device emissions are addressed by ICES-003, which incorporates the same list of exempted devices as FCC Section 15.103, citing transportation vehicles, test equipment, and the like. Explicitly excluded, however, are digital devices used in machinery th | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
of the measured frequency as d > 
.
10
m, –10.5 dB; 10
).