There as problems testing for radiated emissions and immunity in
a unlined screened room, especially or physically large systems.
Reflections create complex frequency dependant patterns of
nodes and anti-nodes across the room. these patterns will also
vary in a complex and almost unpredictable way depending on
the shape and positioning of the equipment under test. Variations
of over 20dB readily occur. Such tests do not comply with the
open area test site requirements of both American and European
emission tests. Even if you use a technical construcion file route
for European compliance the competent body will probably require
a very large margin over the standard limits to allow for
uncertainty.
Immunity measurements of small items can be made in a unlined
screened room by using a small isotropic antenna in a feedback
loop to level out the field at the test point but this approach
fails when the equipment is comparable is size with the node to
node spacing 1875 to 150mm over the freqency range 80 -1000MHz.
Nick Rouse
