Sorry I'm a few days late in responding to the previous thread on this subject, but I delayed in order to re-check my data before posting this as the last time this topic was discussed (August 99) it seemed to be quite controversial! However, I have a concern that some of the recent postings regarding this topic [on the use of a 3 meter anechoic chamber for FCC emissions testing for Part 15 compliance] may cause some confusion or be misunderstood by some. This concern has prompted me to put the following together!
The FCC [in Part 15.31 paragraph (a)(6)] mandates that all-digital devices shall be measured for compliance using ANSI C63.4-1992. (Note: There is an alternative route to compliance using CISPR 22!) Now ANSI Standard C63.4-1992 allows the use of "an absorber lined room" as an alternative test site in 5.4.2 "providing:-- -----the alternative site meets the site attenuation requirements of 5.4.6 over the volume occupied by the EUT (5.4.6.5) -----and the conducting ground plane requirements of 5.4.3. -----and in cases of disagreements, "final radiated emissions tests performed at an OATS meeting the requirements of 5.4.1 (Reference Test Site) and 5.4.6 (Validation Requirements) take precedence" Practically speaking a 3-meter anechoic chamber that is allowably per this requirement would conform to the following:- 1 Have a range distance of 3 meters. 2 For a conforming 3-meter chamber, have a practical minimum size of approx. 20' wide x 29' long x 18' high. This provides an ANSI 2 meter 'test volume" diameter. There are dimensional differences depending on the manufacturer of the chamber and the "test volume" required. 3 Be used in a semi-anechoic configuration. That is there must be an effective ground plane on the floor (per 5.4.3) It can be insulated but not covered with absorber! The usual way to achieve this is to have the floor absorber removable. Another method (but maybe not too practical!) is to cover the absorber (if ferrite) with thin metal sheet(s) when doing emissions measurements! 4 The height of the room must be sufficient to allow for the 1 to 4 meter antenna height scan plus antenna. This usually means about 18' high minimum which allows for close to a 2 meter max. height antenna with a 0.25m clearance to floor and ceiling. 5 It must comply with the NSA measurements per ANSI C63.4-1992 including section 5.4.6.5 "NSA for Alternative Test Sites" which specifies using multi-point NSA measurements over the "test volume" of the EUT An anechoic chamber that conforms to the above can be used for emissions testing to FCC part 15 for both Class A & Class B. Tony Colorado --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
