antenna-theory.com

[SuperDave]

I would like to use a Bluetooth module (with built in antenna) but need to put it in a NEMA metal box for weather protection. I know the box isn't RF proof so there will probably be some leakage around the rubber seals but I had the thought of putting a slot or slots in the front panel under a label so that the box would still be sealed for weather but perhaps "leak" better for RF.

Is it worth the trouble? Is there an optimum slot size, number, distance from the module?

As you can tell I have enough RF knowledge to be dangerous but not enough to solve this issue (which may not actually need solving). The module only has to radiate about 2-3 meters from the box. I'm not looking for extended or even normal Bluetooth range.

Thanks for the nice site.

[bigSteve]

I haven't done this before, so this post will basically give a sketch of how I would solve the problem.

First, if you are only interested in weather-proofing, possibly a thin wood, plastic or styrofoam box would disturb your antenna much less (and wouldn't necessarily require a slot at all) than a metal enclosure.

Second, if you already have the metal box and want to try it, I think it is doable. The slot should be as large as possible; the smaller it is the less radiation will escape through it. The radiation will be primarily in the direction of the slot, and will not have much less power in other directions.

To get it to work will require a guess and test methodology. Experiment with the distance from the slot and the orientation of the module within the box. Test the wireless connectivity for each setup until you find something that works.

Sorry I can't offer specifics, I haven't implemented what you're doing, but this is how I would go about it.

[SuperDave]

The metal box is a requirement unfortunately, otherwise I'd use a plastic bag! A big hole is hard to cover with a label while maintaining structural integrity. So if the rubber seal doesn't leak enough I'll experiment with slots. Easy enough to mill.

Thanks again for the site and the help.

Dave