For our first reverberation chamber we modified an old relay rack!
Here is the original relay rack with everything taken out just waiting to be sanded and modified.
We sanded all the bonding surfaces and made some front panels. In the picture above we have the front panels installed and the chamber is waiting to have the sides and the back put installed.
One the sides and back were installed we applied copper tape (with a conductive glue) to all the seems and holes inside the chamber. Looking inside the chamber you can see what this looks like.
Before we installed the stirrer we put some antennas inside the box to measure the resonant frequencies of the box and to estimate their "Q". In the picture above the chamber is hooked up with 4 dipole antennas. We are limited in measuring the actual Q since we can not measure the power that is reflected from the transmit antenna back into the spectrum analyzer. We do have a directional coupler on order which will allow us to make this measurement. Our measured "loaded Q's" represent a lower bound on the unloaded Q of the box.
This simply chamber has the stirrer mounted on a rod which starts outside the chamber, is grounded to the chamber and brings a shaft down from the ceiling. At the moment this is turned manually. Above we are constructing the support mechanism that allows us to raise, lower and turn the stirrer from outside the metal box!
Above is our first (very simple) stirrer (a square 40cm by 30cm) made of aluminum (roof flashing) and some aluminum stock to add stiffness. The Lucite block is an antenna!
This is a picture of our three axis dipole antenna. There is another single dipole mounted in the top of the Chamber and a broad band antenna mounted in the bottom of the chamber The broad band antenna starts loosing its sensitivity below about 500 Mhz (details to follow).
First data on the effectiveness of the stirrer was taken at the end of June 2007. We examined the orientation of the Electric field over a narrow range of frequencies as we moved the stirrer. We have done this at several key frequencies. We can see the transition to a reverberation mode.