PD 6591:1996

Foreword
1. Scope
2. Object
3. Definitions
3.1 Semi anechoic enclosure
3.2 Fully anechoic enclosure
3.3 Chamber factor
3.4 Grey factor
4. Theory concerning the use of chamber
     factors
5. Equipment for chamber factor measurements
6. Reference site
6.1 Reference site for semi anechoic enclosures
7. Procedure for Chamber factor measurements
7.1 Semi anechoic enclosure
8. Determination of chamber factor and grey
     factor
8.1 Semi anechoic enclosure
9. Application of chamber factor and grey
     factor
10. Error budget
11. References
Figures
Annex A Specification of reference radiator
Annex B Examples of results of normalized
site attentuation measurements and chamber
factor measurements
B.1 Measurement methods
B.2 Test equipment
B.3 Reference sites
B.4 Calibration of broadband attennas
B.5 Results
B.6 Conclusions

Gives help with the evaluation of shielded anechoic enclosures used for radiated emission measurements.

This guideline deals with the application of absorber-lined enclosures for radiated-emission tests according to CISPR 16 [1], CISPR 11 [2], CISPR 22 [3] and EN 50147-2 [4] in the frequency range of 30 - 1000 MHz.

Standard site acceptability criteria based on normalized site attenuation (NSA) measurements are given in [1, 4]. The chamber factor concept shall provide a method for more detailed evaluations of the performance characteristics of enclosures. Measured chamber factor data can, furthermore, be used to correlate test results from equipment under test (EUT) to open site results. Whereas NSA evaluates chamber performance with respect to theoretically calculated reference values, chamber factors are derived from comparative measurements between an enclosure and a good reference site.

If the measured site attenuation exceeds the “± 4 dB??-limit only in the frequency range of 30 - 200 MHz and by not more than ± 12 dB, then the methods described in this report may be applied. For equipment that is no larger than half a wavelength (including cables) the enclosure can then be used at the expense of higher test uncertainty in the lower frequency range.