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Materials to attenuate radio range?

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 06 October, 2006 » Materials to attenuate radio range? « Previous Next »

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Mattau
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Username: Mattau

Post Number: 1
Registered: 09-2006

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Posted on Tuesday, 26 September, 2006 - 08:30 am:   Edit Post Delete Post Print Post

Hi,

I'm working with some small wireless sensors, and want to experiment with the wireless network and a few other programs I've written.

The problem is at the lowest radio power of -10dBm they have a range in excess of 150 metres; you can see if I want to seperate 10 sensors so that they can only communicate with a few others I'm going to need an enormous area.

Does anyone have any suggestions on what I might be able to wrap the sensors in to bring the range down to a more reasonable 5-10 metres?

Thanks
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Mattau
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Posted on Tuesday, 26 September, 2006 - 08:32 am:   Edit Post Delete Post Print Post

and I should add that the nodes transmit at around 900 MHz
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Terry
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Post Number: 252
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Posted on Tuesday, 26 September, 2006 - 08:37 am:   Edit Post Delete Post Print Post

When I want to do short range tests I just remove the aerial, at the low power no harm has ever been done.
The other way is to make an attenuator.

Terry
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Zeitghost
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Post Number: 387
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Posted on Tuesday, 26 September, 2006 - 12:26 pm:   Edit Post Delete Post Print Post

Stick each one in a biscuit tin with the lid on?

That's a real biscuit tin, not a plastic one... :o)
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Obiwan
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Posted on Wednesday, 27 September, 2006 - 12:17 am:   Edit Post Delete Post Print Post

You can use aluminum foil, make a mechnical connection to ground.

Regular window screen works well also. Make sure you have the actual metal screen, not the nylon fibers dipped in plastic.

Just ground part of (and you can solder to at least one type of the metal screen) and you have a Faraday shield (which is what you're looking for).

Unless you're working with high frequency, just about any metal with holes in it will work (you don't need holes, but you might need ventilation or power connections).

If you look at a microwave door you'll see the "screen" inside of it. If those holes were much larger the microwave radiation would excape.

That's high frequency, and you can see how big those holes are.

Just about any metal between the two will work, but it's better if it's grounded.
Do Not Hit The Fly That Lands On The Tigers Head.
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Scott2734
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Posted on Wednesday, 27 September, 2006 - 03:32 am:   Edit Post Delete Post Print Post

I have a friend that plays with radio and he made a room out of copper mesh. It kills any signal before it can get out. I think the same thing can be accomplished , but in a smaller package.
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Zeitghost
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Posted on Wednesday, 27 September, 2006 - 09:01 am:   Edit Post Delete Post Print Post

Like a biscuit tin perhaps?

It was not a joke...

The spaces around the lid allow some signal leakage, but should attenuate the signal somewhat.

Try it & see what happens.
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Obiwan
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Posted on Wednesday, 27 September, 2006 - 06:29 pm:   Edit Post Delete Post Print Post

The leakage through that biscuit tin would only be at very high frequency, above microwave.

If he gets any leakage out of there, then he's on the wrong forum to start with.

Unless you and I have different tins in mind.
Do Not Hit The Fly That Lands On The Tigers Head.
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Zeitghost
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Post Number: 392
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Posted on Thursday, 28 September, 2006 - 08:40 am:   Edit Post Delete Post Print Post

There's no leakage whatever through the tin.

The leakage is through the join between the tin and the lid, and there won't be a lot of that... so as attenuators go, it's cheap & you can eat the biscuits (or cookies if you're a cousin).
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Mattau
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Posted on Monday, 02 October, 2006 - 03:06 pm:   Edit Post Delete Post Print Post

Thanks for your help.

We tried tin foil ann around a cardboard box and that blocked all the signal. We then tried a canister with foil wrapped around it and that kind of worked, it was like a waveguide funnelling the signal upwards with some leakage on the horizontal plane (where the sensors were located) but it wasn't reliable enough.

I think were going to have to settle for winding the (flexible) antenna into small coils not as scientific as i'd like but it seems to do the job.

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