Conformity Magazine - April 2008 - (Page 30)

Reg. Body Test Conditions Standard & section (s) -43 dBm = 50 nW E = sqrt (30 x 50x10-9) / 3 = 409 μV/m = 52 dB μV/m Comments The FCC limit of 250 μV/m (or 48 dB μV/m) is only 4 dB lower than ETSI limit, and both are reasonably comparable. According to ETSI specified measurement method in sec. 8.2.1.3 of the above standard, power is measured indirectly by measuring electric field at 3 m from antenna, and converted to power by using common formulas between E-field and ERP or EIRP given in Annex D of that standard. The recommended antenna size is less than λ/10; therefore, the power at the input of the antenna must be much higher than -43 dBm (50 nW), due to poor antenna efficiency. Example 3a: 2.4 GHz digitally modulated FH systems Looking at Table 3a, we notice that both standards specify power limits, which appear very close in value. The FCC is generally more generous with limits, 1W power output at full hopping rate in this case. However, looking at exact definition of the power in both cases, we find some differences. The FCC specifies peak conductive power, which seems clear and straight forward, but no specific method is prescribed to measure it. The antenna gain is assumed to be less than 6 dBi; therefore, FCC-15.247 sec.(a) & (b) are applicable. But ETSI specifies EIRP which, in this case, is essentially a conducted measurement as below, rewriting Equation 1: P (dBm) = A + G + 10 log (1/x) =< 20 Where P is the EIPR limit, A is the average output power (sec. 5.7.2.2), G is antenna gain, and x is the transmitter duty cycle. Comments Since the typical antenna size used (1 to 1.5 cm) in such devices is comparable with the wavelength λ =12.5-cm, at such frequencies though still close to λ/10, better antenna efficiency compared to other two devices is expected. Therefore, it may be assumed that the actual radiated power will not be too low. However, ETSI includes antenna gain G into the limits; thus, sufficient margin should be provided at the conducted power output point (P1) to account for the antenna gain. For instance, say the duty cycle is 35%, the antenna gain is 2.5 dB, and other losses are 1.5 dB. This gives maximum allowed average output A as: A =< 20 -2.5 – 3.97 or A =< 13.5 dBm FCC 2400 -2483.5 MHz Min 15 hop Ch, 125 mW pk. FCC 15.247 (b) -1 conducted. And for 75 hop Ch, 1W pk. conducted 2400 -2483.5 MHz Min 15 hop Ch. 100 mW EIRP ETSI ETSI EN 300 328 sec. Table 3a: Power limits, 2.4 GHz band devices, operating with FH spread spectrum modulation Reg. Body Test Conditions Standard & section (s) FCC 2400 -2483.5 MHz ant gain 6 FCC 15.247 sec. e dBi, PSD, 8 dBm in 3-kHz BW 2400 -2483.5 MHz. PSD 10 mW in 1 MHz BW EIRP ETSI EN 300 328 sec. (4.3) ETSI Table 3b: Power limits 2.4 GHz devices working with non-FH digital spread spectrum 30 Conformity April 2008 http://www.amphenol-aerospace.com/filtercatalogs http://www.amphenol-aerospace.com http://www.amphenol-canada.com

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Conformity Magazine - April 2008 NewsBreaks Editor’s Note Mandatory Analog Cellular Service Ends FCC Releases Quarterly Reports on Consumer Inquiries and Complaints New Standards List Released for The EU’s Low Voltage Directive FDA Issues Notification on Unretrieved Device Fragments FDA Offers Guidance on Waivers for In-Vitro Diagnostic Devices ESD Open Forum Emerging Issues in Standards Challenges in Testing Design Fundamentals Focus on... New Products Product Reviews Premarket Approval Application Guidance Issued by FDA New Jersey Enacts Electronic Waste Recycling Regulations A New U.S. Standard for Workstation and Computer Design Might the CPSC Hold Retailers Accountable for Safe Products? CPSC Loses “Sole Toy Tester” CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - April 2008

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