My Faraday Cage Test: Is this bogus or not?

Calling all electrical engineers, HAM operators, or EMP shielding experts!

I have 8 Baofeng UV-5R radios. 2 of them we use around the farm. But the other 6 have just been sitting in their cardboard boxes . Figured it was time to protect them.

So, I can pack 2 radios in a standard 1 gal paint can as the outer container -- seams and lid taped with aluminum tape.

I also used mylar bags because they have proven to provide some shielding (some of them anyway). In the experiment, I used two small bags (for which I didn't have shielding ratings), and one large bag that has a "EMI Shielding (MIL-B-81705-Rev-C)" rating of "40 db between 1 & 10 GHz". But, since I'm not a REAL engineer, I scarcely understand what a "db" is which is why I am wanting input on my experiment.

In the experiment I used two Baofeng UV-5R radios. From what I have been able to determine, these have about 130 db of dynamic range at most frequencies (see attached doc where a guy did some testing), which I THINK means that in order to keep the radio in the faraday cage from receiving the signal, I have to provide at least 130 db of shielding. I went under that assumption, anyway.

So here's what I did.

• Turned on both radios and turn the volume all the way up on the one that went inside the shielding materials.
• Put the receiving radio in 1 unrated mylar bag and sealed the opening with aluminum tape: radio received transmission loud and clear.
• Put the sealed bag in a second unrated mylar bag and sealed the opening with aluminum tape: radio received transmission, loud and clear, but with maybe a hint of attenuation -- a little weaker and not as prone to feedback at close range.
• Put the two mylar bags with radio inside a 1 gal metal paint can and seal up the lid with aluminum tape: could still hear the transmission well but with quite a bit more perceived attenuation.
• Put paint can in 40 db rated mylar bag WITHOUT sealing it up -- top of bag completely open: the signal completely blocked IF the transmitting radio was placed at the side of the bag, but the signature was NOT blocked if the transmitting radio was placed at the open end of the bag.

So, it seems that the 2 unrated mylar bags + the sealed up paint can ALMOST blocked the signal. It just needed a little bit more shielding to block the signal completely.

I'm sure that I was not getting 40 db of shielding from the open mylar 40 db rated bag because it was not sealed up. BUT, just for cautious calculations, let's just say I actually got 40 db from it. 130 db - 40 db = 90 db. So IF it actually takes 130 db of shielding to block the radio signal, then the paint can with the 2 unrated mylar bags was giving at least 90 db of shielding. Right?

Is this a decent test? Does anyone have more reliable information about the dynamic range of the Baofeng UV-5R radio? [And, of course, this test is with MHz and and not EMP frequencies, but I don't know how to test using those frequencies.]

Thanks!

--- Lobanz

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My Faraday Cage Test: Is this bogus or not?