From Wireless
From WiFi in your HiFi to Bluetooth in medical devices, the use of wireless communications has become ever more prevalent in products that have typically relied upon wired interfaces. While the availability of RF modules may have alleviated the need for manufacturers to become proficient in RF design, the complexity of approvals for wireless devices requires a much greater depth of regulatory knowledge. This article reviews the EMC and radio test requirements in the US, Canada and the European Union for devices that incorporate wireless modules, with the aim of providing guidelines to assist in understanding the test and regulatory requirements for both the wireless function and the complete product. Modular Approvals in Canada and the United States The Federal Communications Commission (FCC) allowed modular approvals for several years before finally formalizing requirements through a Public Notice in June 2000[1]. This Public Notice outlined a series of 8 requirements, which, if met, allow a device to obtain a modular approval. Modular approval enables other manufacturers to incorporate an authorized module into a product without having to re-evaluate or recertify the wireless function of the composite unit. As of April 1, 2005 there have been 959 grants issued for modular approvals.
Industry Canada (IC) followed shortly behind the FCC, incorporating nine similar modular approval requirements into their radio test standard for low power devices, RSS-210[2]. If a product incorporates a device that has been approved against these requirements, then no additional tests or certifications are required for the wireless functions included in that module. The combined IC and FCC requirements are, in summary:
1. The modular transmitter must have its own RF shielding (the shielding must enclose all RF circuitry).
2. The modular transmitter must have buffered modulation/data inputs.
3. The modular transmitter must have its own power supply regulation to ensure that the module will comply with Part 15 requirements regardless of the design of the power supplying circuitry for the host. (U. S.)
4. The certification submission shall contain a detailed description of the configuration of all antennas that will be used with the module.
5. The modular transmitter must either be permanently attached or employ a "unique" antenna coupler (at all connections between the module and the antenna, including the cable). The "professional installation" provision of Section 15.203 may not be applied to modules. (U. S.)
6. The modular transmitter must be tested in a stand-alone configuration. (U.S.)
7. Unless battery powered, it must comply with the AC line conducted requirements found in Section 15.207 (U. S.)
8. The module shall meet Industry Canada's certification labeling requirements. The host device shall also comply with the certification labeling requirements of each of the modules it contains. (Canada)
9. The modular transmitter must be labeled with its own FCC ID number. Unless this label is visible form the outside of the host device, the host device must also display a label referring to the enclosed module's FCC ID. (U. S.)
10. The modular transmitter must comply with any specific rule or operating requirements applicable to the transmitter and the manufacturer must provide adequate instructions with the module to explain any such requirements.
11. The host device and all the separately certified modules it contains jointly meet the RF safety requirements of RSS-102, if applicable. (Canada)
12. The modular transmitter must comply with any applicable FCC RF exposure requirements. (U.S.)
The FCC requires that the module manufacturer ensure that the integrator of the module be given adequate information in terms of:
The FCC also allows for a limited modular approval for modules that do not meet all of their requirements provided that the Grantee (typically the module manufacturer) can demonstrate that it will retain control over the final installation of the device, such that compliance of the end product is assured. The grant of equipment authorization for the module would specifically state that the module is only approved for use when installed in devices produced by a specific manufacturer, typically the Grantee.
There are some commonly overlooked issues that manufacturers using modules should keep in mind. Most of these originate from not reviewing the conditions of the FCC grant for the module or from unfamiliarity with the FCC's rules. The grant can be easily obtained through the FCC's website[3]. Examples of grants for a limited modular approval and a full modular approval are given in Figures 1 and 2 respectively.
Figure 1: Grant for Limited Modular Approval
Figure 2: Grant for Full Modular Approval
Common mistakes include:
In some of the listed examples the modular approval would be invalid and a new application would need to be filed with the appropriate agencies before the product could be sold. Although some test data from the original modular approval might be used, product release dates can be severely impacted if the project plan did not account for the time needed to obtain certifications.
The European Union's Approach to Embedded Radio Frequency Units The EU's rules are very different from those in both the US and Canada. With the FCC and Industry Canada the requirements for modules are regulated through third-party certification. Manufacturers who use such modules can rely on the certification obtained by the module manufacturer (plus associated documents). In contrast, in the EU, products with a wireless interface do not require third-party certification. Rather, the Radio and Telecommunications Terminal Equipment Directive (R&TTE D) requires that the manufacturer issue their own Declaration of Conformity, declaring compliance with the essential requirements of all applicable directives. The level of testing required for products that use a radio module is, therefore, a little less clear since the manufacturer (or whomever places the product on the market) bears the full responsibility for demonstrating compliance with the regulatory requirements.
In the absence of strict certification for Europe, there is no guaranteed route for modular approvals. Rather, the focus is on approval of the final product. It is the sole responsibility of the person/group placing a product on the market, to ensure that the final product meets all the essential Directive requirements. However, there is flexibility in how the company may make that decision. The company placing a product on the market may use the modular approvals approach as a guide to make an informed decision regarding their product's compliance.
Some of the EU's harmonized radio performance standards (e.g. EN 300 328 v1.5.1) and EMC standards (e.g. EN 301 489-17 v1.2.1) reference testing methods for "host dependent" equipment and plug-in cards, allowing a module manufacturer to test a module as a stand-alone device. EN 301 489-17 contains the following statements:
Where a specific combination of host equipment and a radio equipment part is tested as a composite system for compliance, repeat testing shall not be required for those other combinations of hosts and radio equipment parts which are based on substantially similar host models in the circumstance that the variations in mechanical and electrical properties between such host models are unlikely to significantly influence the intrinsic immunity and unwanted emissions of the radio equipment part
Further guidance for multi-radio and combined radio and non-radio equipment is given in two documents issued by the European Telecommunications Standards Institute (ETSI). The first, TR 102 070-2 V1.1.1[4], addresses the application of radio standards and the second, TR 102 070-1 V1.1.1[5], addresses the application of EMC standards. These two documents contain multiple scenarios as to how the radio function is incorporated into the final system, and these various scenarios can be broken down into two main categories:
1. If the host system has no functionality without the wireless interface then the manufacturer should apply the appropriate radio-specific standards for radio performance, EMC and safety to the complete device.
2. If, however, the host system has other functions then the manufacturer would apply the product specific standards for EMC and product safety to the compete system and only apply the radio-specific standards to the radio function for those tests that are not covered by the product-specific requirements.
It should be noted that these are not harmonized standards (EN) and are therefore only guidance documents. They can be quite useful when a Notified Body is asked to assess compliance.
The integrator of a module that has been tested against the appropriate radio and EMC standards may choose to use the module's test reports as the basis for his declaration of compliance of the main system provided that the test configuration for the module adequately represents the configuration of the module in the host system. This does not necessarily mean that the integrator will do no testing, but instead could justify performing a reduced sub-set of tests, in order to make their decision about the end product's compliance.
If the integrator is using the module with the same operating software and the test conditions for the module are consistent with those of the final product then most, if not all transmitter-related tests might be considered covered by the module's test report. Receiver-related tests (specifically receive or stand-by mode spurious emissions) would probably need to be re-evaluated to demonstrate that the additional circuitry built around the module still complies. For immunity tests, the module integrator needs to assess which of the radio modules ports would need to be re-tested given the nature of the additional circuitry provided by the host system, and also determine which of the host systems interface ports need to be evaluated. Some areas where the module's test report might not prove adequate in supporting a Declaration of Conformity for the end product would include:
If the module is used in multi-function equipment where the radio is only one of the functions, then the complete system would always need to be assessed against the product specific emissions and immunity EMC standards. For example, an audio component that connects into a HiFi system and has an 802.11 (WiFi) interface to wirelessly access music from a PC should meet all relevant requirements of the product specific EMC standards (EN 55013 and EN 55020) as well as the relevant requirements of the radio standards (EN 300 328 and EN 310 489-17). Only where the frequency range or test methods of the product-standard tests do not overlap with the radio-specific standards, or where the radio specific standards have additional requirements, does the manufacturer need to assess the applicability of the module's test report for demonstrating compliance of the final system.
One very important area that is often overlooked occurs when a radio module is incorporated into a medical device. The medical device EMC standard, IEC/EN 60601-1-2 Edition 2[6], which is used in the USA, Canada and EU has wording that addresses the performance of radios installed in medical devices that provides an exemption for the main transmit signal from the radiated emissions limits referenced in the medical EMC standard (provided that they meet the national requirements), but states that all other emissions should meet the radiated emissions limits. There are many cases where the radio standard's limits for transmitter radiated spurious emissions are less restrictive than the IEC/EN 60601-1-2 limits. Thus, application of the incorrect limits can make the task of compliance unnecessarily difficult.
Regardless of the geographical market, any manufacturer who intends to use a radio module needs to work closely with the module manufacturer. A thorough review of the module's test report, the conditions of its authorization, the end product specification, and knowledge of the various test standards are necessary. Without comparing the various product- and radio-specific standards for EMC and safety, it is impossible to ensure that the final product has been evaluated against all appropriate requirements with the minimum number of tests. n
References 1. Federal Communications Commission Public Notice DA 00-1470 Released June 25, 2000 - available through www.fcc.gov/oet
2. Industry Canada Radio Standards Specification RSS-210 Issue 5, November 2001 - available through http://strategis.ic.gc.ca
3. FCC generic search web page is online at https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm
4. ETSI TR 102 070-2 V1.1.1 (2002-11), Technical Report: Electromagnetic compatibility and Radio spectrum Matters (ERM); Guide to the application of harmonized standards to multi-radio and combined radio and non-radio equipment; Part 2: Effective use of the radio frequency spectrum - available through www.etsi.org
5. ETSI TR 102 070-1 V1.1.1 (2002-07) Technical Report: Electromagnetic compatibility and Radio spectrum Matters (ERM); Guide to the application of harmonized standards to multi-radio and combined radio and non-radio equipment; Part 1: ElectroMagnetic Compatibility- available through www.etsi.org
6. IEC/EN 60601-1-2:2001 Medical electrical equipment ¡ª Part 1-2: General requirements for safety - Collateral standard: Electromagnetic compatibility - Requirements and tests
About the Authors Mark Briggs is a Principal Engineer with Elliott Labs (www.elliottlabs.com), a compliance engineering laboratory and TCB (Telecommunications Certification Body) based in Silicon Valley. Mark has been involved in EMC and Radio testing for the last 11 years.
Michael Derby is a Senior Engineer with RFI Global Services Ltd. (www.RFi-global.com), a provider of a wide range of compliance services, based in the UK. Michael has been involved in EMC and Radio testing for the last 14 years. © Copyright 2007 Conformity |
