Section 5.4.2 of ANSI C63.4 says, "Measurements can also be made where the requirements of 5.4.6 [NSA] are not met but it can be demonstrated to the relevant authority that the results achieved are equivalent to those obtained at an open area test site over the frequency range at which measurements are made."
Several supplies of compact semi-anechoic chambers claim a 6 dB variation in site attenuation vs the required 4 dB. If the claims are true, it would appear that one could successfully test products in a compact chamber if 2 dB of margin were subtracted from the test limits. I would like to hear from anyone who has been successful in convincing the FCC to accept test data taken in a non-compliant compact chamber that is corelated with the NSA requirements.
