# I/O panel filtering for shielded room

We are looking into setting up a very basic shielded chamber inside a small room at my company to be able to perform some basic relative radiated EMC measurements.

We will buy a somewhat cheap spectrum analyzer together with a set of near field probes and a biconical antenna, and want to have a room where we can perform measurements with as little interference as possible.

So I’ve been looking into doing a very cheap DIY shielded chamber inside the room, by building a wooden frame and wrapping chicken wire around the frame with thick aluminum foil to seal all joints.

The only thing I still feel unsure about is how to do the filtering for the I/O panel. What we need to get into the chamber is the following signals:

• 230V/50 Hz power
• USB 2.0
• Ethernet
• Coax antenna connector for biconical antenna
• Two BNC connectors for DC power supply
• SMA connector for various RF stuff

So my question is how I would filter all of these signals in suitable ways? Our plan right now is to slap ferrites on all signals, but I don’t think that will accomplish very much. What would be a better way?

EDIT: For anyone looking for additional answers to this question, I asked Keith Armstrong over at emcstandards.co.uk and he very kindly made this blog post about my question: https://www.emcstandards.co.uk/constructing-io-panels-for-shielded-rooms

Otherwise you need a 6" by 6" by 20" power_line filter, bonded to the steel/copper of the walls.

By the way, aluminum oxide forms INSTANTLY upon exposure to air, thus the aluminum will not make ohmic contact between the various sheets.

There will be high capacitance as you crumple the sheet_edges together, but not ohmic.

C = Eo * Er * Area/Distance

C = 9-12 farad/meter * (Area = 2cm * 50cm)/100 micron

C = 9e-12 farad/meter * (100 cm * cm) / 0.0001millimeter

C = 9e-12 farad * 100/0.0001 * cm/meter * cm/millimeter

C = 9e-12 * 1Million * 0.01 * 10

C = 9e(-12 + 6 -2 +1) = 9e-7 = 0.9 uF

which may be adequate even at 10MHz.

Correct answer by analogsystemsrf on December 29, 2020