Hi Jeff If you're having a problem with ambient noise, you need a shielded room first! A steel shielded room will isolate your EUT to about -100dB from 200kHz to >20GHz. The foam or ferrite is then added to prevent internal reflections/standing waves. But foam and or ferrite will only absorber RF to approx. -20 to -40 dB. (You need long lengths of foam to get even -10dB at low frequencies approx. 30MHz!). If you're only doing pre-compliance you could use only the shielded room, but be aware that reflections will distort your readings. Sometimes people only add absorber at the critical areas I.E. front and back walls. Again, this is a compromise as there will still be reflections from the other walls, ceiling etc. Small shielded rooms can be found in the used market, so can foam. My advice would be to start with just a shielded room, and try it out. You can always add absorber later, but be aware that if you add foam, a lot of your working area will be used up, whereas ferrite only takes about 1 1/2" of space per surface! Also be aware that ferrite is HEAVY, so original construction and installation of the shielded room would need to take this into account. Hope this helps Tony O'Hara LARCTEC Marketing
