Steve - in answer to your question regarding cables and configurations for EMI testing:
>To my knowledge there exists two methods of cable termination, passive or >active. Under what circumstances for example does a EMI laboratory test >engineer determine what should be the appropriate method for configuring >data cables for termination, length, orientation/position on a 1.0m X 1.5m X >80cmH non-conductive table-top. > >As an example, ethernet switches, hubs, servers, repeaters etc. all use >cables of undetermined lengths. What would be the appropriate configuration >for testing an ethernet print server with 4 ea. parallel ports, and 4 ea >serial ports? Therefore, given the above question, do the current >international/domestic regulations contain B&W answers to this type of >question or does their exist some level of interpretation here. ANSI C63.4 (1992) section 6 states that one of each kind of functional port must be connected to a peripheral consistent with actual usage. All other ports of that functional type must be connected to a cable unless it can be shown that the additional cables have no significant effect on the emissions level. CIPSR 22 further defines the "significant effect" as being 2dB (if I recall correctly - and this may be in the second ammendment to CISPR 22). The length of the cables should be consistent with typical usage (form ANSI C63.4). If the typical length can vary then ANSI C63.4 states that a 1m cable should be used, CISPR 22 states that the length shall be sleected to produce maximum disturbance. The length to be used has been discussed several times on the forum - 3m would seem to be the common "worst case". Another approach is to use a variety of lengths if there are multiple ports of the same type. Thus, for your ethernet print server, one serial and one parallel port connected to typical peripherals (e.g. printers) via typical length cables (or 3m cables if "typical" varies), remaining ports with cables connected of the typical (or 3m or various lengths) and either terminated to more peripherals or unterminated or with termination resistors. The ethernet port(s) - one ethernet port to a peripheral (e.g. PC) which could be located remotely (say 30m away) and connected by a cable that lies on ground plane. remaining ethernet ports connected via typical length (or 3m) cables that may be looped between ports (use crossover cables) or terminated in a loop-back (to ensure the link remains active). Regards, Mark Mark Briggs [email protected]
