ARRL

Part 15 - Radio Frequency Devices

FCC Part-15 Rules: Unlicensed RF Devices

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Overview

Hams are very familiar with Part 97 of Title 47 of the Code of Federal Regulations. These are the rules that govern ham radio. There are other Parts in Title 47 that govern other radio services. Part 15 of Title 47 of the Code of Federal Regulations is important to amateurs because it regulates low power, unlicensed devices that could cause interference to the Amateur Radio Service and vice versa. Part 15 covers an assortment of electronic equipment that generates RF energy whether it's intentional, unintentional or incidental. Amateurs will need to consider Part 15 as it relates to digital devices, computers, low-powered, unlicensed transmitters, electrical devices and any other "generic" device that might generate RF in the normal course of its operation.

What is overheard on the air, or on Internet newsgroups and discussion forums is any indication, hams don't understand much about Part 15. There are a lot of "urban myths" that tend to confuse an already-confusing topic. These web pages explain the sections of Part 15 that are especially important to amateurs.

Definitions

Let's first define the most important terms that apply to any discussion of Part 15 rules. Some of these definitions are taken directly from the FCC rules. The applicable Part 15 rule section is indicated with the section symbol (§). Actual FCC rules are in italics in this document.

Interference: The effect of unwanted energy due to one or a combination of RF emissions, radiation, or induction upon reception in a radiocommunication system, manifested by any performance degradation, misinterpretation, or loss of information which could be extracted in the absence of such unwanted energy.

Harmful interference: § 15.3 (m) Harmful interference. Any emission, radiation or induction that endangers the functioning of a radio navigation service or of other safety services or seriously degrades, obstructs or repeatedly interrupts a radiocommunications service operating in accordance with this Chapter. The rules for nearly every licensed radio service prohibit harmful interference and that includes the Amateur Radio Service.

Spurious Emission: Emission on a frequency or frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products, but exclude out-of-band emissions.

Intentional radiator: § 15.3 (o) Intentional radiator. A device that intentionally generates and emits radio frequency energy by radiation or induction. This term generally means "radio transmitter." Examples are cordless telephones, baby monitors or garage-door openers.

Unintentional radiator: § 15.3 (z) Unintentional radiator. A device that intentionally generates radio frequency energy for use within the device, or that sends radio frequency signals by conduction to associated equipment via connecting wiring, but which is not intended to emit RF energy by radiation or induction. Examples include computer systems and superheterodyne receivers.

Incidental radiator: § 15.3 (n) Incidental radiator. A device that generates radio frequency energy during the course of its operation although the device is not intentionally designed to generate or emit radio frequency energy. Examples of incidental radiators are dc motors, mechanical light switches, etc.

Digital device:§ 15.3 (k) Digital device. (Previously defined as a computing device). An unintentional radiator (device or system) that generates and uses timing signals or pulses at a rate in excess of 9,000 pulses (cycles) per second and uses digital techniques; inclusive of telephone equipment that uses digital techniques or any device or system that generates and uses radio frequency energy for the purpose of performing data processing functions, such as electronic computations, operations, transformations, recording, filing, sorting, storage, retrieval, or transfer. A radio frequency device that is specifically subject to an emanation requirement in any other FCC Rule Part or an intentional radiator subject to Subpart C of this Part that contains a digital device is not subject to the standards for digital devices, provided the digital device is used only to enable operation of the radio frequency device and the digital device does not control additional functions or capabilities. Note: Computer terminals and peripherals that are intended to be connected to a computer are digital devices.

Class A digital device: A Class "A" digital device is a digital device that is marketed for use in a commercial, industrial or business environment.

Class B digital device: A Class "B" digital device is a digital device that is marketed for use in a residential environment. Examples of such devices include, but are not limited to, personal computers, calculators, and similar electronic devices that are marketed for use by the general public. Class B equipment, intended for use in a residential environment where the likelihood of RFI is greater, must meet much stricter RF emission limits than the Class A devices.

Carrier-current system: § 15.3 (f) Carrier current system. A system, or part of a system, that transmits radio frequency energy by conduction over the electric power lines. A carrier current system can be designed such that the signals are received by conduction directly from connection to the electric power lines (unintentional radiator) or the signals are received over-the-air due to radiation of the radio frequency signals from the electric power lines (intentional radiator).

Myths About Part 15

There are a lot of urban myths about Part 15 rules and devices. The first is that their signal levels are very small and it is not likely that they will cause harmful interference. Although this is true in most cases, the radiated emissions levels in Part 15 were designed to protect one neighbor's television reception from another neighbor's video game, as an example. The permitted radiation levels are not enough to always protect sensitive amateur reception. As one example, intentional radiators and carrier-current devices are permitted a field strength of 30 microvolts/meter at 30 meters distance from the source. On HF, this legal signal, if heard on an 80 meter half-wave dipole, would result in a received signal of S9+15 dB on most receiver S meters! This clearly would be harmful interference in the Amateur Radio Service.

Many hams believe that all devices regulated by Part 15, including transmitters and digital devices, are "type accepted" by the FCC, with testing in the FCC Lab. Type acceptance has actually been written out of the FCC rules. Devices that were Type Accepted under the old rules are now subject to Certification or a Declaration of Conformity. To obtain Certification, a manufacturer supplies test data to the FCC, usually from a laboratory that the FCC knows and trusts, and Certification is usually issued on the basis of the test data and other information about the product. In a Declaration of Conformity, the manufacturer issues a formal statement to the FCC that the device has been tested at an accredited laboratory and that it complies with the rules.

Although the FCC can call in equipment for testing, in almost all cases, the FCC does not actually perform testing on equipment covered by Part 15. They usually review information and test data supplied by the manufacturer. Most computing devices are subject to Certification or a Declaration of Conformity.

 

Verification

The majority of other devices, however, including carrier-current devices, are subject only to Verification. Verification is a self-approval process where the manufacturer performs the necessary tests and determines that the device complies with the rules. It is not necessary for the manufacturer of a Verified device to notify the FCC or to send them test data.

 

Who is Responsible?

With all of these confusing rules and many devices manufactured under an "honor system," it is surprising that things work so well. In many cases, Part 15 devices are not located near another radio receiver, so the absolute maximum limits in Part 15 are enough to prevent interference. In the cases of interest to amateurs, however, a Part 15 device can be very close to a sensitive receiver -- maybe even in our own homes. Under those circumstances, interference can occur.

 

Harmful Interference

The FCC rules require the equipment manufacturer or importer to design and test his products to ensure that they do not exceed the absolute maximum limits. In addition, the FCC requires that Part 15 devices be operated in such a way that they not cause harmful interference. The operator of the Part 15 device is responsible for correcting the interference or to stop using the device if so ordered by the FCC. This can create a very difficult situation. Imagine that the neighbor of a ham goes to a local retail store and buys a Part 15 device. If the device causes harmful interference, the rules place the responsibility of proper operation and correction of the interference on the user. This can put a ham into the unenviable position of having to explain to a neighbor that the device he or she just bought at a local store is being used in violation of federal law! The resultant disagreement is not unexpected.

The Scope of Part 15

Part 15 actually covers a lot of territory. Because of space limitations, only the most applicable sections are included in this chapter. The sections of Part 15 that are most applicable to amateurs include: 15.5(a), (b) and (c) Conditions of Operation, 15.13 Incidental Radiators, 15.17 Susceptibility to interference and sections from Subpart B-Unintentional Radiators (15.101 Equipment authorization of unintentional radiators, 15.105 Information to the user, 15.107 Conduction limits, and 15.109 Radiated emission limits). The pertinent information from these sections follows.

The requirements for these unlicensed RF emitters are complex. To complicate the picture even more, not all unlicensed devices operate under Part 15; some operate under other FCC rule parts. When some of these devices are manufactured, they must have a label stating that the device meets Part 15 specifications and the authorization procedures are outlined in Part 2.

In many cases, Part 15 devices use frequencies allocated to other radio services, including the Amateur Radio Service, on a secondary, non-interference basis. For example, some cordless telephones operate in the 902-928 MHz band, secondary to other users. Some frequency segments, including several in the amateur bands, have been approved for higher power Part 15 devices. In addition, some devices that do not specifically use any frequency, but still may radiate RF energy, are also covered in Part 15.

To help emphasize the secondary status of all devices operated under Part 15, the rules stipulate that the devices must not cause harmful interference to other radio services and must accept any interference caused by the legal operation of other radio services. Amateurs need to know what the manufacturer has told the consumer and what the consumer is supposed to know about the interference potential. Amateurs can often direct consumers to the owner's manual of the affected device for information on the potential for RFI and for its elimination! These rules explain to the consumer whose responsibility it is to resolve the interference.

Part 15 sets out the regulations under which an intentional, unintentional, or incidental radiator may be operated without an individual license. It also contains the technical specifications for various types of devices. These technical specifications include absolute maximum radiated and conducted limits, in addition to the requirements stipulating that no harmful interference may result from the operation of a Part 15 device. In addition, the rules contain administrative requirements and other conditions relating to the marketing of Part 15 devices.

 

Types of Devices

There are a number of types of devices regulated by Part 15. These are the ones that are probably of the most concern to Amateur Radio:

High-power intentional radiators: These devices are specifically authorized as intentional emitters. On some bands, 2.3 GHz using spread spectrum, for example, they can use power levels of up to 1 watt. In other cases, they are specifically limited to a particular field strength. They are authorized to transmit on some amateur bands, on a secondary basis. These devices are certificated.

Low-power intentional radiators: Part 15 rules also permit intentional radiators to operate on nearly any frequency. These low-power intentional radiators are limited to specific field strengths that vary with frequency. The field-strength limits were chosen so that interference is not expected under most circumstances. These devices are certificated.

Unintentional radiators: The most common unintentional radiators are computers or similar digital devices. These have radiated emissions limits above 30 MHz and conducted emissions limits below 30 MHz.

Incidental radiators: These include devices like motors and power lines. Part 15 requires that they use good engineering and that they not cause harmful interference to radio services.

What is the Impact on Amateur Radio?

With all of the Part 15 devices that are out in the world, what are the threats and perceived threats, and how can Amateur Radio tell one from the other? The occasional video game or touch lamp in a neighborhood is a very real problem to the involved ham, but these types of devices only occasionally cause problems and those problems are local in nature. These are best dealt with on a case-by-case basis. The ARRL publishes an excellent book, the ARRL RFI Book, edited by W1RFI (what a perfect call for the League's RFI "guru") and written by a collection of real RFI experts. The League also offers considerable starter information about RFI on its TIS Web page.

But there are other potential problems that can be widespread. These must be dealt with on a broader front. ARRL does this by participation in industry standards organizations, maintaining contact with industry and regular contact with the FCC. The League can also help with individual cases of interference. Many of these potential problems involve various home and area networking products. The ones that have received the most attention of late are home-phone networking devices (HPN), xDSL (digital subscriber lines) and similar devices that put digital signals onto power lines or electrical wiring.

Let's examine these technologies and talk about their possible impact on Amateur Radio.

Equipment Authorization Procedures and Information

No discussion of RFI would be complete without a discussion of FCC equipment authorization procedures which are based on Parts 2, 15, 18 and 68 of FCC rules. Manufacturers can't simply market an RF device without the appropriate FCC approval; standards must be met to insure that the device does not cause undue interference or constitute a hazard to users. These standards apply to a wide range of intentional, unintentional and incidental emitters of RF energy, ranging from unlicensed RF transmitters, such as baby monitors and low-power walkie-talkies to small digital devices to personal computers and peripherals.

Many people think that FCC regulations require that these devices all be tested by the FCC, but in reality, few devices must actually undergo FCC testing. In most cases, the requirements are met by the manufacturer testing the device and either keeping the test results on file or by sending them to FCC, depending on the type of device involved.

The following summary of Part 2, Subpart J, provided by the FCC Equipment Authorization Branch, provides some general information concerning various FCC approval processes for RF devices:

Certification: Requires submittal of an application that includes a complete technical description of the product and a measurement report showing compliance with the FCC technical standards. Devices subject to certification include: low power transmitters such as cordless telephones, garage door opener controls, radio control toys, and security alarm systems, scanning receivers and superregenerative receivers; and, TV interface devices such as VCRs.

Type Acceptance: Similar to certification, except that it typically applies to radio transmitter equipment that will be used in a licensed radio service. Devices subject to type acceptance include: land mobile transmitters such as cellular transmitters, or police, fire and business transmitters; transmitters used in the maritime and aeronautical safety services; and CB and other transmitters used in the Personal Radio Services. Amateur Radio transmitters do not require type acceptance although external HF power amplifiers and kits do require type acceptance.

Notification: Requires submittal of an abbreviated application for equipment authorization, that does not include a measurement report, to the FCC. However, a measurement report showing compliance of the product with the FCC technical standards must be retained by the applicant and must be submitted upon request by the Commission. Devices subject to notification include: point-to-point microwave transmitters; AM, FM and TV Broadcast transmitters; certain microwave auxiliary broadcast transmitters; and, other receivers (except as noted elsewhere).

Verification: Verification is a self-approval process where the applicant performs the necessary tests and verifies that they have been done on the device to be authorized and that the device is in compliance with the technical standards. Devices subject to verification include: business computer equipment (Class A); TV and FM receivers; and, non-consumer Industrial, Scientific and Medical Equipment. Verified equipment requires that a compliance label be affixed to the device as well as information included in the operating manual regarding the interference potential of the device. The wording for the compliance label and the information statement regarding interference problems is included in Part 15 of the FCC Rules. Verified devices must be uniquely identified with a brand name and/or model number that cannot be confused with other devices on the market. However, they may not be labeled with an FCC identifier or in a manner that could be confused with an FCC identifier.

Declaration of Conformity: A Declaration of Conformity is a new approval procedure for personal computers and personal computer peripherals. This authorization is based on a declaration that equipment complies with FCC requirements and it applies only to Class B personal computers and peripherals. A DoC is an alternative to Certification since no application to FCC is required, but the applicant must have the device tested at an accredited laboratory.

Specific information on obtaining an equipment authorization can be obtained from the FCC Web site or from the FCC Application Processing Branch in Columbia, Maryland. Individuals with questions concerning equipment authorization procedures should be addressed to: labinfo@fcc.gov

Interested amateurs can view the FCC equipment authorization database at this Web site:

http://www.fcc.gov/oet/info/database/ead/

The FCC also provides an on-line BBS information service to check the status of equipment authorizations and to learn more about the FCC rules. It can be reached at (301) 725-1072.

General Part 15 Technical Requirements

The following section discusses those sections of Part 15 that are the most important to amateurs.

The following regulations apply to all Part 15 devices:

§ 15.5 General conditions of operation.

(a) Persons operating intentional or unintentional radiators shall not be deemed to have any vested or recognizable right to continued use of any given frequency by virtue of prior registration or certification of equipment, or, for power line carrier systems, on the basis of prior notification of use pursuant to § 90.63(g) of this chapter.

(b) Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, scientific and medical (ISM) equipment, or by an incidental radiator.

(c) The operator of a radio frequency device shall be required to cease operating the device upon notification by a Commission representative that the device is causing harmful interference. Operation shall not resume until the condition causing the harmful interference has been corrected.

(d) Intentional radiators that produce Class B emissions (damped wave) are prohibited.

One point which is echoed throughout Part 15 is the fact that they can't cause harmful interference to other services. This point is illustrated below:

§ 15.13--Incidental radiators--states that "Manufacturers of these devices shall employ good engineering practices to minimize the risk of harmful interference."

Certain Part 15 technical regulations apply to all such devices:

§ 15.15 General technical requirements.

(a) An intentional or unintentional radiator shall be constructed in accordance with good engineering design and manufacturing practice. Emanations from the device shall be suppressed as much as practicable, but in no case shall the emanations exceed the levels specified in these rules.

(b) An intentional or unintentional radiator must be constructed such that the adjustments of any control that is readily accessible by or intended to be accessible to the user will not cause operation of the device in violation of the regulations.

(c) Parties responsible for equipment compliance should note that the limits specified in this part will not prevent harmful interference under all circumstances. Since the operators of part 15 devices are required to cease operation should harmful interference occur to authorized users of the radio frequency spectrum, the parties responsible for equipment compliance are encouraged to employ the minimum field strength necessary for communications, to provide greater attenuation of unwanted emissions than required by these regulations, and to advise the user as to how to resolve harmful interference problem (for example, see § 15.105(b)).

§ 15.17 is especially noteworthy because it advises designers and manufactures of electronic devices that use RF energy to be aware of the potential for RFI from outside sources, such as Amateur Radio! It also advises manufacturers to take appropriate measures to control the susceptibility of their equipment to RFI:

§ 15.17 Susceptibility to interference.

(a) Parties responsible for equipment compliance are advised to consider the proximity and the high power of non-Government licensed radio stations, such as broadcast, amateur, land mobile, and non-geostationary mobile satellite feeder link earth stations, and of U.S. Government radio stations, which could include high-powered radar systems, when choosing operating frequencies during the design of their equipment so as to reduce the susceptibility for receiving harmful interference. Information on non-Government use of the spectrum can be obtained by consulting the Table of Frequency Allocations in § 2.106 of this chapter.

Most Part 15 devices require a label attesting to the potential for interference and to the responsibility of the device operator. The following sections from the rules provide an examples of the labeling requirements:

§ 15.19 labeling requirements.

(a) In addition to the requirements in part 2 of this chapter, a device subject to certification, notification, or verification shall be labeled as follows:

(3) All other devices shall bear the following statement in a conspicuous location on the device:

This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

And:

§15.105--Information to the user.

(a) For a Class A digital device or peripheral, the instructions furnished the user shall include the following or similar statement, placed in a prominent location in the text of the manual:

This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instruction manual, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense.

(b) For a Class B digital device or peripheral, the instructions furnished the user shall include the following or similar statement, placed in a prominent location in the text of the manual:

This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:

Reorient or relocate the receiving antenna. Increase the separation between the equipment and receiver. Connect the equipment into an outlet on a circuit different from that to which the receiver is connected. Consult the dealer or an experienced radio/TV technician for help

 

Absolute Limits

As examples of the actual levels of the absolute limits in Part 15, the tables from Part 15 are reproduced here. These tables are for example only because each contains numerous notes that grant exceptions to these limits for various devices or explain how they are to be applied to different types of unintentional emitters. The notes also permit compliance with certain other regulations or standards in lieu of Part 15. Consult the actual text of Part 15 for more information. In general, the limits in Sections 15.107 and 15.109 apply to unintentional radiators such as computer systems and digital devices.

 

Conducted Limits

§ 15.107 Conducted limits.(a) Except for Class A digital devices, for equipment that is designed to be connected to the public utility (AC) power line, the radio frequency voltage that is conducted back onto the AC power line on any frequency or frequencies within the band 450 kHz to 30 MHz shall not exceed 250 microvolts. Compliance with this provision shall be based on the measurement of the radio frequency voltage between each power line and ground at the power terminals.

(b) For a Class A digital device that is designed to be connected to the public utility (AC) power line, the radio frequency voltage that is conducted back onto the AC power line on any frequency or frequencies within the band 450 kHz to 30 MHz shall not exceed the limits in the following table. Compliance with this provision shall be based on the measurement of the radio frequency voltage between each power line and ground at the power terminals. The lower limit applies at the band edges.

Frequency of Emission (MHz)

Conducted Limit (microvolts)

 

0.45 to 1.705

1000

1.705 to 30

3000

Sec. 15.109 Radiated emission limits.

(a) Except for Class A digital devices, the field strength of radiated emissions from unintentional radiators at a distance of 3 meters shall not exceed the following values:

Frequency of Emission (MHz)

Field Strength (microvolts/meter)

 

30-88

100

88-216

150

216-960

200

Above 960

500

(b) The field strength of radiated emissions from a Class A digital device, as determined at a distance of 10 meters, shall not exceed the following:

Frequency of Emission (MHz)

Field Strength (microvolts/meter)

 

30-88

90

88-216

150

216-960

210

Above 960

300

 

Carrier-Current and Similar Devices Must Meet Radiated Limits For Intentional Emitters

§ 15.109 (e) Carrier current systems used as unintentional radiators or other unintentional radiators that are designed to conduct their radio frequency emissions via connecting wires or cables and that operate in the frequency range of 9 kHz to 30 MHz, including devices that deliver the radio frequency energy to transducers, such as ultrasonic devices not covered under Part 18 of this Chapter, shall comply with the radiated emission limits for intentional radiators provided in Section 15.209 for the frequency range of 9 kHz to 30 MHz.

 

Intentional Radiators

Part 15, Subparts C and D addresses RF emission limits from different types of intentional radiators such as remotely controlled garage door opener controls, R/C toy cars, hand held automobile door lock and burglar alarm controls, cordless telephones (including both base and handset), wireless baby monitors, toy "walkie-talkies", dog trainers, carrier-current and perimeter-protection systems. Amateurs may encounter such devices, either as the source or the victim of an RFI problem.

The Part 15 regulations on intentional radiators are complex, taking page after page to explain all the nuances. Interested readers should refer to the FCC rules for further information about this equipment and its associated emission limits since the Part 15 radiation limits contain many exceptions..

Part 15 essentially permits very low power, unlicensed intentional radiators on nearly any frequency, including all amateur bands. The following table, from § 15.205, shows the frequencies for which intentional radiators cannot be operated. There are a number of notes in the actual text of the regulations; refer to Part 15 for more information.

As described in § 15.109(e), carrier-current devices and devices that conduct their signals via interconnecting wires must meet the limits for intentional radiators on HF.

Restricted Bands of Operation - Intentional Radiators

§ 15.205 Restricted Bands of Operation (a) Except as shown in paragraph (d) of this section, only spurious emissions are permitted in any of the frequency bands listed below:

MHz

MHz

MHz

GHz

0.090-0.110

16.42-16.423

399.9-410

4.5-5.15

0.495-0.505

16.69475-16.69525

608-614

5.35-5.46

2.1735-2.1905

16.80425-16.80475

960-1240

7.25-7.75

4.125-4.128

25.5-25.67

1300-1427

8.025-8.5

4.17725-4.17775

37.5-38.25

1435-1626.5

9.0-9.2

4.20725-4.20775

73-74.6

1645.5-1646.5

9.3-9.5

6.215-6.218

74.8-75.2

1660-1710

10.6-12.7

6.26775-6.26825

108-121.94

1718.8-1722.2

13.25-13.4

6.31175-6.31225

123-138

2200-2300

14.47-14.5

8.291-8.294

149.9-150.05

2310-2390

15.35-16.2

8.362-8.366

156.52475-156.52525

2483.5-2500

17.7-21.4

8.37625-8.38675

156.7-156.9

2655-2900

22.01-23.12

8.41425-8.41475

162.0125-167.17

3260-3267

23.6-24.0

12.29-12.293

167.72-173.2

3332-3339

31.2-31.8

12.51975-12.52025

240-285

3345.8-3358

36.43-36.5

12.57675-12.57725

322-335.4

3600-4400

13.36-13.41

     

 

Radiated Emissions Limits

On other frequencies, § 15.209 states that the radiated emission limits of intentional radiators generally can't exceed the field strength levels specified in the following table:

Frequency (MHz)

Field Strength (microvolts/meter

Measured Distance (meters)

 

0.009-0.490

2400/F(kHz)

300

0.490-1.705

24000/F(kHz)

30

1.705-30.0

30

30

30-88

100

3

88-216

150

3

216-960

200 3

Above 960

500 3

Except as provided in paragraph (g), fundamental emissions from intentional radiators operating under this Section shall not be located in the frequency bands 54-72 MHz, 76-88 MHz, 174-216 MHz or 470-806 MHz. However, operation within these frequency bands is permitted under other sections of this Part, e.g., Sections 15.231 and 15.241. In the amateur 2-meter band, for example, these regulations would permit an intentional radiator to run a transmitter power of about 4 nanowatts into a half-wave dipole, resulting in a field strength of 150 microvolts/meter at a point 3 meters away from the dipole center.

To relate this to receiver S unit readings (50 uV at 50 ohms = S9 and an S unit = 6 dB), a 144-MHz field of 150 microvolts/meter would result in an S9 meter reading if 2.2 dBi gain antennas were used on each end (half-wave dipoles in free space). Of course, this is only 3 meters from the source. If the source were located 30 meters away, the signal would be about an S6. On 3.5 MHz, the permitted field strength is 30 microvolts/meter at 30 meters distance. A field of this strength would give an S9+15 dB reading to a half-wave dipole on 80 meters.

 

Periodic Radiators

In addition, Part 15 permits a number of "periodic" devices to transmit on all permitted frequencies at a much higher power. Periodic devices are characterized as various control and signaling devices with very limited transmission times.

Here are the rules on Periodic emitters. They can operate on nearly any frequency above 70 MHz (except those prohibited under 15.205). This includes all amateur bands above 144 MHz.

Section 15.231 Periodic operation in the band 40.66 - 40.70 MHz and above 70 MHz. (a) The provisions of this Section are restricted to periodic operation within the band 40.66 - 40.70 MHz and above 70 MHz. Except as shown in paragraph (e) of this Section, the intentional radiator is restricted to the transmission of a control signal such as those used with alarm systems, door openers, remote switches, etc. Radio control of toys is not permitted. Continuous transmissions, such as voice or video, and data transmissions are not permitted. The prohibition against data transmissions does not preclude the use of recognition codes. Those codes are used to identify the sensor that is activated or to identify the particular component as being part of the system.

The following conditions shall be met to comply with the provisions for this periodic operation: (1) A manually operated transmitter shall employ a switch that will automatically deactivate the transmitter within not more than 5 seconds of being released. (2) A transmitter activated automatically shall cease transmission within 5 seconds after activation. (3) Periodic transmissions at regular predetermined intervals are not permitted. However, polling or supervision transmissions to determine system integrity of transmitters used in security or safety applications are allowed if the periodic rate of transmission does not exceed one transmission of not more than one second duration per hour for each transmitter. (4) Intentional radiators which are employed for radio control purposes during emergencies involving fire, security, and safety of life, when activated to signal an alarm, may operate during the pendency of the alarm condition.

(b) In addition to the provisions of Section 15.205, the field strength of emissions from intentional radiators operated under this Section shall not exceed the following:  

Fundamental Frequency (MHz)

Field Strength of Fundamental (microvolts/meter)

Field Strength Of Spurious Emissions (microvolts/meter)

 

40.66-40.70

2250

225

70-130

1250

125

130-174

1250 to 3750**

125 to 375**

174-260

3750

75

260-470

3750 to 12500**

375 to 1250**

Above 470

12500 1250

** linear interpolations [Where F is the frequency in MHz, the formulas for calculating the maximum permitted fundamental field strengths are as follows: for the band 130-174 MHz, uV/m at 3 meters = 56.81818(F) - 6136.3636; for the band 260-470 MHz, uV/m at 3 meters = 41.6667(F) - 7083.3333. The maximum permitted unwanted emission level is 20 dB below the maximum permitted fundamental level.]

(1) The above field strength limits are specified at a distance of 3 meters. The tighter limits apply at the band edges.
(2) Intentional radiators operating under the provisions of this Section shall demonstrate compliance with the limits on the field strength of emissions, as shown in the above table, based on the average value of the measured emissions. As an alternative, compliance with the limits in the above table may be based on the use of measurement instrumentation with a CISPR quasi-peak detector. The specific method of measurement employed shall be specified in the application for equipment authorization. If average emission measurements are employed, the provisions in Section 15.35 for averaging pulsed emissions and for limiting peak emissions apply. Further, compliance with the provisions of Section 15.205 shall be demonstrated using the measurement instrumentation specified in that section.
(3) The limits on the field strength of the spurious emissions in the above table are based on the fundamental frequency of the intentional radiator. Spurious emissions shall be attenuated to the average (or, alternatively, CISPR quasi-peak) limits shown in this table or to the general limits shown in Section 15.209, whichever limit permits a higher field strength.
(c) The bandwidth of the emission shall be no wider than 0.25% of the center frequency for devices operating above 70 MHz and below 900 MHz. For devices operating above 900 MHz, the emission shall be no wider than 0.5% of the center frequency. Bandwidth is determined at the points 20 dB down from the modulated carrier.
(d) For devices operating within the frequency band 40.66 - 40.70 MHz, the bandwidth of the emission shall be confined within the band edges and the frequency tolerance of the carrier shall be + 0.01%. This frequency tolerance shall be maintained for a temperature variation of -20 degrees to +50 degrees C at normal supply voltage, and for a variation in the primary supply voltage from 85% to 115% of the rated supply voltage at a temperature of 20 degrees C. For battery operated equipment, the equipment tests shall be performed using a new battery.
(e) Intentional radiators may operate at a periodic rate exceeding that specified in paragraph (a) and may be employed for any type of operation, including operation prohibited in paragraph (a), provided the intentional radiator complies with the provisions of paragraphs (b) through (d) of this Section, except the field strength table in paragraph (b) is replaced by the following:
 

Fundamental Frequency (MHz)

Field Strength of Fundamental (microvolts/meter)

Field Strength Of Spurious Emissions (microvolts/meter)

 

40.66-40.70

1000

100

70-130

500

50

130-174

500 to 1500**

50 to 150**

174-260

1500

150

260-470

1500 to 5000**

150 to 500**

Above 470

5000 500

** linear interpolations [Where F is the frequency in MHz, the formulas for calculating the maximum permitted fundamental field strengths are as follows: for the band 130-174 MHz, uV/m at 3 meters = 22.72727(F) - 2454.545; for the band 260-470 MHz, uV/m at 3 meters = 16.6667(F) - 2833.3333. The maximum permitted unwanted emission level is 20 dB below the maximum permitted fundamental level.] In addition, devices operated under the provisions of this paragraph shall be provided with a means for automatically limiting operation so that the duration of each transmission shall not be greater than one second and the silent period between transmissions shall be at least 30 times the duration of the transmission but in no case less than 10 seconds.

Section 15.35 Measurement detector functions and bandwidths. The conducted and radiated emission limits shown in this Part are based on the following, unless otherwise specified elsewhere in this Part:

(a) On any frequency or frequencies below or equal to 1000 MHz, the limits shown are based on measuring equipment employing a CISPR quasi-peak detector function and related measurement bandwidths, unless otherwise specified. The specifications for the measuring instrument using the CISPR quasi-peak detector can be found in Publication 16 of the International Special Committee on Radio Interference (CISPR) of the International Electrotechnical Commission. As an alternative to CISPR quasi-peak measurements, the responsible party, at its option, may demonstrate compliance with the emission limits using measuring equipment employing a peak detector function, properly adjusted for such factors as pulse desensitization, as long as the same bandwidths as indicated for CISPR quasi-peak measurements are employed.

Note: For pulse modulated devices with a pulse-repetition frequency of 20 Hz or less and for which CISPR quasi-peak measurements are specified, compliance with the regulations shall be demonstrated using measuring equipment employing a peak detector function, properly adjusted for such factors as pulse desensitization, using the same measurement bandwidths that are indicated for CISPR quasi-peak measurements.

(b) On any frequency of frequencies above 1000 MHz, the radiated limits shown are based upon the use of measurement instrumentation employing an average detector function. When average radiated emission measurements are specified in the regulations, including emission measurements below 1000 MHz, there is also a limit on the radio frequency emissions, as measured using instrumentation with a peak detector function, corresponding to 20 dB above the maximum permitted average limit for the frequency being investigated unless a different peak emission limit is otherwise specified in the rules, e.g., see Section 15.255. Unless otherwise specified, measurements above 1000 MHz shall be performed using a minimum resolution bandwidth of 1 MHz. Measurement of AC power line conducted emissions are performed using a CISPR quasi-peak detector, even for devices for which average radiated emission measurements are specified.

(c) Unless otherwise specified, e.g. Section 15.255(b), when the radiated emission limits are expressed in terms of the average value of the emission, and pulsed operation is employed, the measurement field strength shall be determined by averaging over one complete pulse train, including blanking intervals, as long as the pulse train does not exceed 0.1 seconds. As an alternative (provided the transmitter operates for longer than 0.1 seconds) or in cases where the pulse train exceeds 0.1 seconds, the measured field strength shall be determined from the average absolute voltage during a 0.1 second interval during which the field strength is at its maximum value. The exact method of calculating the average field strength shall be submitted with any application for certification or shall be retained in the measurement data file for equipment subject to notification or verification.

15.231(e) authorizes many types of periodic emitters. Typical examples include remote-reading thermometers and other devices. The rules, as defined in 15.35, allow the manufacturer to determine the average power in a 100 millisecond time period. The device further may not transmit for more 3.33% of the time, with a minimum "silent" period of 10 seconds between transmissions.

Periodic radiators are actually fairly common around 433.92 MHz, a frequency used for Industrial, Scientific and Medical use or for various remote-control operations in other parts of the world. The RF modules designed and sold for those uses are very usable under Part 15 rules. 433.92 MHz is, in most areas, used for various control link functions; it is not likely that harmful interference from this "legal" signal will occur. In general, periodic radiators do not cause significant harmful interference.

 

Unlicensed Part 15 Bands

Band

Typical Use

160 - 190 kHz

Hobbyist

510 - 1705 kHz

Hobbyist

1.705 - 10 MHz

General

13.553 - 13.567 MHz

General

26.96 - 27.28 MHz

Hobbyist, walkie-talkie, baby monitor, etc.

40.66 - 40.70 MHz

Perimeter protection systems, control systems

43.71 - 44.49 MHz

Cordless telephones

46.60 - 46.98 MHz

Cordless telephones

48.75 - 49.51 MHz

Cordless telephones

49.66 - 50.0 MHz

Cordless telephones, walkie-talkie, baby monitor, etc.

72.0 - 73.0 MHz

Auditory assistance devices

74.6 - 74.8 MHz

"

75.2 - 76.0 MHz

"

88.0 - 108.0 MHz

Hobbyist, miscellaneous

174.0 - 216.0 MHz

Biomedical telemetry on unused TV channels

890.0 - 940.0 MHz

Measurement systems, Amateur

902.0 - 928.0 MHz

Multiple Part 15 uses, Amateur

1.91 - 1.93 GHz

Personal Communications Service (PCS)

2.39 - 2.4 GHz

PCS, Amateur

2.435 - 2.465 GHz

"

2.9 - 3.26 GHz

Automatic vehicle identification systems (AVIS)

3.267 - 3.332 GHz

AVIS, Amateur

3.339 - 3.3458 GHz

AVIS, Amateur

3.358 - 3.6 GHz

AVIS, Amateur

5.15 - 5.35 GHz

Unlicensed National Infrastructure Devices (U-NII)

5.725 - 5.825 GHz

U-NII, other unspecified uses

10.500 - 10.550 GHz

Multiple Part 15 uses, amateur

24.075 - 24.175 GHz

Multiple Part 15 uses, amateur

46.7 - 46.9 GHz

Vehicular collision avoidance/radar systems

76.0 - 77.0 GHz

Vehicular collision avoidance/radar systems, Amateur

There are a number of bands set aside for higher power intentional radiators. These bands are used for various unlicensed walkie-talkies, baby monitors, cordless telephones and the like. These include:

PART 18: Industrial, Scientific and Medical Regulations

The FCC rules in Part 18 of CFR 47 deal with industrial, scientific, and medical equipment (ISM) that emits electromagnetic energy in the RF spectrum. As with the equipment covered by Part 15, the ISM equipment addressed here is also a potential source of RFI. The most applicable sections of Part 18 follow.

The basic FCC definitions of ISM equipment are given in five paragraphs of §18.107. Industrial, scientific, and medical (ISM) equipment (ISM devices) generate and use locally RF energy for industrial, scientific, medical, domestic or similar purposes, excluding applications in the field of telecommunication. Typical ISM applications are the production of physical, biological, or chemical effects such as heating, ionization of gases, mechanical vibrations, hair removal and acceleration of charged particles. They also include industrial heating equipment, medical diathermy equipment, ultrasonic equipment, consumer ISM equipment (domestic microwave ovens, jewelry cleaners for home use, and ultrasonic humidifiers.)

§ 18.109 directly addresses the interference issues of ISM equipment. Basically ISM equipment should be of "good engineering design" with adequate filtering to provide adequate suppression outside of the ISM bands. § 18.111 outlines the basic RFI operating conditions for users of ISM equipment and §18.115 outlines procedures for eliminating and investigating harmful interference from ISM equipment. This section states that "(a) The operator of ISM equipment that causes harmful interference to radio services shall promptly take appropriate measures to correct the problem."

However, that provision "shall not apply in the case of interference to an authorized radio station or a radiocommunication device operating in an ISM frequency band." And, it "shall not apply in the case of interference to a receiver arising from direct intermediate frequency pickup by the receiver of the fundamental frequency emissions of ISM equipment operating in an ISM frequency band and otherwise complying with the requirements of this part." These conditions are very similar to the RFI operating conditions for Amateur Radio service. In other words, if the ISM equipment is operating properly in its assigned band, any RFI it is causing must be accepted or corrected by the entity that is receiving the interference, including amateurs.

§ 18.213 is important because it alerts consumers in the operations manual or packaging material to the interference potential and simple measures which can be taken to correct the problem. §§ 18.301-311 deal with the operating frequencies and field-strength limits of the ISM bands. These bands are distributed across the spectrum in small segments from 6.78 MHz to 245 GHz.

The following ISM bands overlap all or portions of certain amateur bands:

ISM Frequency (MHz)

Tolerance

Amateur Band

915 MHz

+-13.0 MHz

902-928 MHz

2,450 MHz

+-50.0 MHz

2300-2310 and 2390-2450 MHz

5,800 MHz

+-75.0 MHz

5.650-5.925 GHz

24,125 MHz

+-125.0 MHz

24.0-24.25 GHz

245.00 GHz

+-1.0 GHz

241-250 GHz

The field-strength and conduction limits depend on the band of operation and the equipment used. Interested readers should refer to these sections of the FCC rules and regulations for a complete listing of the bands and limits.

How Bad Can It Get?

Interference from Part 15 devices can get pretty bad. While a single video game in a neighborhood may cause a local problem, some interference from other devices can be much more pervasive. The ARRL has been involved with a case of Part 15 interference that is literally nationwide in scope. It has taken over a year for even partial resolution. The whole story can be read on the "Wireless Modem and Telephone Jacks" article on the ARRL Technical Information Service Web page. In this case, the Phonex Corporation manufactured wireless modem jacks that operated on 3.53 MHz! These were installed by TCI Cablevision (now owned by AT&T) by the thousands. The result in some areas was that the lower 50 kHz of the 80 meter band was virtually useless for Amateur Radio. Both companies extended immediate cooperation to resolve the interference, but in spite of excellent cooperation, some hams are still experiencing problems over a year later and there are probably still numerous unreported cases.

Clearly, Part 15 devices can pose a serious threat under some circumstances.

 

Always a Problem?

Does this mean that every Part 15 device is harmful to Amateur Radio? Not at all. Many hams successfully use computers in their ham shack, affecting only a few spot frequencies in some cases. Other hams have a neighbor with a computer that radiates over half a band. Some high-voltage power lines are clean as a whistle, while other residential power lines have greater than S9 noise levels 24 hours a day. At ARRL Headquarters, our local-area network uses twisted pair wiring throughout the building with high-speed digital signals bouncing around the building day and night, yet W1AW and the ARRL HQ Operators Club Station, W1INF, hear just fine.

Clearly, every new Part 15 devices does not mean the "End of Amateur Radio As We Know It." Part of the role of the ARRL is to identify potential problem devices, assess the impact of those devices, and direct HQ staff and volunteer resources to work with manufacturers to resolve problems before they become large problems.

Several manufacturers of Part 15 devices have contacted the ARRL, asking for information about Amateur Radio and interference, so they can avoid harmful interference. The League staff, naturally, was pleased to help. Maybe some problems have been nipped in the bud! There are hams everywhere, in industry, on committees and at test labs across the country. Amateur Radio has been fortunate that when many of these issues come up, hams recognize potential problems and either help their companies or organizations deal with the problem directly. Others contact the ARRL for help.

The FCC's Role

What is the FCC's role in all this? Naturally, as regulators, they enforce the rules. This includes oversight of the manufacturers as they build and test their products for Verification under Part 15 rules. The FCC is also concerned with the requirement that Part 15 devices not cause harmful interference to radio users. The levels of permitted radio emissions from Part 15 devices are high-Amateur Radio can only live with them because the rules also protect against harmful interference. It is critical that the FCC continue to enforce the rules about interference from Part 15 devices. This can be the weak point in the chain.

As a ham, imagine that your neighbor goes to a local retail store and buys a networking device. If that device has harmful interference, you have the unenviable task of going to your neighbor and trying to explain complex Part 15 regulations. What your neighbor will hear is that you are making the outrageous claim that a device he just bought at a local store is in violation of federal law. When you tell your neighbor that his brand-new device is causing interference to you, he or she may get a look of glee and say, "Aha! The tables have turned!" This is a diplomacy problem that will be hard to solve.

How does the FCC view all this? Perhaps the most encouraging sign is summarized in the statement by Commissioner Susan Ness: (http://www.fcc.gov/Speeches/Ness/States/stsn810.html)

"Our predecessor agency, the Federal Radio Commission, was established in 1927. The raison d'etre for that commission was the need to prevent harmful interference to services using the airwaves. Managing the spectrum to prevent interference remains one of this agency's most important priorities today.

"In the digital age, an extraordinary number of devices have the potential to improve the quality of life. Many of these same devices also have the potential to cause harmful interference. This interference may degrade consumers' radio and TV reception, or it may jeopardize air traffic control systems, police and fire communications, or other services essential to public safety. That's why we have technical specifications for intentional and unintentional radiators-to ensure that new products can continue to be designed without jeopardizing radio communications.

"How can we best ensure compliance with these rules-without unnecessarily impeding the flow of useful products into the marketplace? That's what this item is about.

"In the past, we have liberalized equipment authorization procedures for products which were determined to present minimal risk of causing harmful interference. We are extending that liberalization today. A proceeding is already on the drawing board to take that process a step further-to allow other organizations, instead of the Commission, to certify products.

"I strongly support reducing unnecessary paperwork and delays. But we must not diminish our commitment to prevent harmful interference to authorized radio communications. Whatever our equipment authorization procedures, there will remain a danger that some products will not be designed to minimize the danger of interference. And there will also remain a problem of individuals who construct or operate transmitting devices with disregard for our rules.

"Our responsibility to prevent harmful interference can only be fulfilled if we are prepared to follow through with credible enforcement. I sincerely hope that agency resources that are freed up, by today's order and by the third-party certification rulemaking, will be redirected to enforcement activities, so that instances of harmful interference can be swiftly remedied."

 

In Practice

How is this sentiment being put into practice with the FCC? In an ideal world, hams who experience harmful interference from Part 15 devices could call the FCC and say, "Go forth and enforce." But FCC resources are very limited and the FCC simply cannot track down every emitter and then deal with the Part 15 operator.

The needs of Amateur Radio are unique, with hams routinely dealing with signal levels lower than most services consider acceptable. This would be an impossible task for the FCC to manage, and if they did, Amateur Radio might not like the line in the sand the FCC might draw with respect to signal levels. Instead, Amateur Radio gets the best of all worlds when the FCC relies on Amateur Radio to work with the Part 15 manufacturers and operators to voluntarily resolve harmful interference. As seen in much of this article, the ARRL has played a strong role in that process. Individual hams play a strong local role, too.

But hams can't do it alone. Without that FCC "big stick" being held in the background, some Part 15 manufacturers and operators will not understand the rules or the importance of following them. FCC information plays a key role in helping to encourage everyone to do the right thing. Right now, the FCC information on interference from devices regulated by Part 15 is pretty scant. The ARRL is working with the FCC to fix this, through Ed Hare's contact with the FCC Call Center staff.

Together, they are determining what type of FCC information could be sent out on a routine basis to help amateurs better deal directly with Part 15 manufacturers (probably through ARRL) and operators of Part 15 devices (often a local problem involving a neighbor or utility operator).

Links to More Information

The Official Web Site of the Government Accountability Office provides an Abstract on Potential Spectrum Interference Associated with Military Land Mobile Radios, GAO-06-172R, December 1, 2005. The American Telecommunications Certification Body (ATCB) provides Part 15 information, including the following pages: · In AmericanTCB's "Ask The Experts" Forum you may post questions about determining the appropriate standards, test set ups and suites, and certification strategies for the US and the World (hosted by Interference Technology). · The AmericanTCB FCC Rule Part Limit Calculator & Tools provides a few limit calculators for various FCC Rule Parts.

ARRL Technical Information Service
Email TIS
ARRL Regulatory Information Branch
Email RIB
RFI - RFI General Information and Home Page
RFI - Wireless Modem Jacks
RFI - Electrical and Power Line
FCC Home Page
FCC Amateur Rules -- Part 97
FCC Rules - Part 15 and Other
Telecommunications and Radiocommunication Equipment
This site contains searchable databases of radiocommunication and telecommunications equipment that has been certified for use in Canada.
FCC Part 15 Enforcement Letters
Inside FCC Part 15 and Canada's Corresponding Standards
The FCC's Part15 Rules and Regulation and 802.11b emissions in the ISM 2.4GHz Band
Using Part 15 Wireless Ethernet Cards For Amateur Radio
Part 15 Devices (The World Above 50 MHz)
QST December 2001, pp. 82-83
Equipment Authorization FAQs
The Association for Maximum Service Television, Inc., (MSTV) provides Your neighbor's Static; a video on the dangers of operating unlicensed radio devices in the broadcast television band.

This information was prepared as a membership service by the American Radio Relay League, Inc., Technical Information Service, 225 Main St., Newington, CT 06111 (860) 594-0214. Email: tis@arrl.org (Internet). ARRL HQ is glad to provide this information on the Web free of charge as a service to League members and affiliated clubs.

If you have any questions concerning the reproduction or distribution of this material, please contact: tis@arrl.org)