Conformity Magazine - January 2009 - (Page 32) The FCC requires, in OET-65 bulletin sec. 2 [4], that in any multiple transmitter configuration no transmitter is allowed more than 5% of the limits of the SAR threshold. In this way, one can have up to 20 such devices co-existing in a close proximity or in a single enclosure/area. The following expression gives a conceptual relationship for individual power density of i-th transmitter Pdi to the limit PL and the total Pd (tot) at a given point. The quantity PL is the maximum acceptable power density (limit) at a given point in space. This formula clarifies the regulatory requirements: Pd (tot) = Σ i =1N Pdi < PL power densities can be added; and Pdi < 0.05 PL where PL is the upper limit of the power density at a given frequency. The actual measurement method of the field can best be explained by Health Canada Safety Guide-6, sec 2.4.1 [14]: E = sqrt(1/n Σn E2 ) which is the RMS of all the electric field values. The actual calculation of Pd at any point in the field due to all collocated transmitters is not easy; therefore, FCC requires that it be measured instead. EU Regulations for Equipment with Multiple Transceivers It may be noted that, in both North American and the EU, the EMC regulatory thinking about radiated and spurious emissions is similar, but the main difference is about the equipment immunity from ambient disturbances. EU regulations place emphasis on the product immunity as performance issue, whereas regulations in North America do not. The EU regulations for combined equipment which has at least one radio fall under directive 1999/5/EC, also known as the R&TTE Directive [8]. Articles 3.1 and 3.2 of this directive provide basis for the radio equipment testing. The testing rules for combined equipment are guided by a two-part document, ETSI TR 102 070 (1 & 2). The combined equipment is subject to article 3.1(b) conformance, according to standard EN 301-489-1 [11] and other technology related parts, that is, the generic EMC for the radio related equipment. One requirement of this standard is the RF radiated immunity of the combined product. Classification of Combined Equipment In the ETSI TR 102 070 (1 & 2) document, seven physical implementation scenarios of the combined equipment which include a radio are considered. The Part 1 of the document 32 Conformity JAnUAry 2009 explores conditions in which testing may be necessary according to article 3.1(b), while Part 2 looks more closely at the implementation of the radio with respect to appropriate use of spectrum (article 3.2 of R&TTE Directive). Operational and Functional Dependencies: According to ETSI TR 102 070-1 sec. 5, the combined equipment is divided in three categories based upon equipment operational and functional dependencies, based on whether all, only one, or none of the sub-equipment or parts within the seven configurations can operate independently. These dependences also consider whether the sub-equipment gets its power and controls from the main or common source. Based upon these dependencies, the emission and immunity tests for the combination are prescribed. Combined equipment is required to comply with article 3.1(a) and (b) of the R&TTE Directive. The article 3.1(a) implies public safety from emissions (SAR) assessment, though it is not stated explicitly. It may be considered equivalent of the FCC and Industry Canada SAR and RF safety requirements. Article 3.1(b) requires generic EMC compliance which includes immunity testing. But, does it imply collocation interference? We will investigate that question in the next section. Antenna Constraints & Individual Assessment: Another set of classification are given in ETSI TR 102 070-2 sec 6, which places combined equipment with radio in seven possible combinations scenarios, based upon the following factors in various configurations of the final equipment for (re)assessment, whether: • Radio modules can be assessed for conformance purpose separately (or not); • The antenna is integral to the radio module or not; • The radio function is dependant upon power supply and controls from the main product; • A radio product has an embedded non-radio function in it. Based upon these factors, an assessment is made whether testing is required (or not) according article 3.2 of the R&TTE Directive, which is about spectrum usage in the proper way. Such testing becomes quite complex since many details regarding frequency accuracy, modulation methods and other transceivers characteristics are to be tested. There is no antenna-distance rule for the combined equipment in the EU regulations, as in the FCC grant note (20 cm). More detailed testing of the combined product is required when the antenna has been changed from the original manufacturer design, or a non-radio module is plugged into a radio product (part-2 sec. 6.6). [14]
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