[RFI] RF shielding using aluminum foil tape-Fabricating Aluminum Foil Enclosures

Wed Jan 12 21:01:14 EST 2005

RF shielding using aluminum foil tape
Fabricating Aluminum Foil Enclosures

Hello to all RFI members,
I believe this topic comes within the subject matter of this list.
This is my first posting.
Please excuse me if it dose not.

My project is to construct an antenna-switching unit for a multiple radio
station using vacuum relays.
In the frequency range of 1.8 to 30 MHz and at the power level of 1500 watts
I am hopping to achieve full isolation between each port of the unit without
any bandpass filtering.
I am considering to place each vacuum relay used within it's own small box
made out of heavy construction cardboard.
The cardboard box would then be covered with aluminum foil tape.
The aluminum foil tape with the glue backing normally found at local Home
Depot stores.
The RF connections for each vacuum relay would be made with Coax. The center
conductor going to the vacuum relay and the shield connected to the aluminum
foil covering the box. Another thought would be to mount SO-239's onto the
side of the box and use coax jumpers between each relay.

How much shielding can I expect from this type of enclosure?
Will I need to use and if so how many multiple layers of the aluminum tape?
Should both the inside and outside of the box be covered with the aluminum
I understand the skin depth of copper to be 0.0026 inch @1 MHz and 0.00047
inch @ 30 MHz.
What would the skin depth be for aluminum and dose it apply to this

I am trying to reach the full isolation advantage offered by the use of the
vacuum relays.
Should I consider putting a shielded baffle inside the box to isolate the RF
contacts of the relay from each other?
Should the shield on the Coax run up to the relay contact to eliminate the
stray RF pickup within the box?

I suspect that I will have to connect two or three vacuum relays in series
to obtain the wanted isolation.
The end filter assembly will probably look like a very large IF section from
an old tube radio receiver.

Another question for comments:
If I substitute the cardboard with a tin can.
Covering the inside of the tin can with the aluminum foil tape.
I know I have seen copper plated steel chassis on old AM transmitters.

With the availability of today's building materials, PVC and copper pipe,
plastics, aluminum and copper foils the projects are endless. The
traditional hard enclosures and chassis construction can be so much

Thanks for your help,
Rich AA2MF
rcariello at si.rr.com

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