Inside FCC Part 15 and Canada's Corresponding Standards

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.

Part 15 Device	Subpart	Industry Canada Regulation
Information TechnologyEquipment	Subpart B	ICES-003
TV receivers and cable system devices	Subpart B	BETS-7
Low-power transmitters	Subpart C	RSS-210
Unlicensed Personal Communications Services	Subpart D	RSS-213
Table I. Comparison of Part 15 and Industry Canada regulations for the same devices.

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:

Figure 1. Tested DoC label.	Figure 2. Assembled DoC label.

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 of the measured frequency as d > /2.

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

310 m, –10.5 dB; 1030 m, –9.5 dB
103 m, +10.5 dB; 3010 m, +9.5 dB

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.