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433Mhz rf sheilding

Hi to all. I am using an old microwave oven to sheild a 433.92Mhz receiver , for testing purposes , and have a few questions.

If I put a transmitter(433Mhz) in the microwave and close the door the signal is quite well attenuated , 30-40Db or so on the spectrum analyser.The analyser just has a piece of wire as an antenna , and when you open and close the door you can see the obvious attenustion of the signal.This is more of a reletave measurement than absolute. Surely the microwave should block all of the signal , seing that the wavelength is much longer than a 2.54Ghz signal , which I hope it blocks totally!! These transmitters are only about 10mW or so , compared the the microwave signal in the 100's of watts range!!

There are no wires comming out of the microwave to "carry" the signal out.

Any ideas / suggestions would be appreciated. Cheers Rob

Reply to
seegoon99
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Shielding of microwaves is far from perfect.

Reply to
OBones

the shielding only has to shield 2.54G for safety. what it does at other frequencies is more or less irrelevant

martin

After the first death, there is no other. (Dylan Thomas)

Reply to
martin griffith

microwave ovens rely heavily on a feromagnetic strip around the door seal (usualy a half inch brown strip of plastic), this is very efective at microwave frequencies as it has a very high absorption, however i dont think it is likly to be very efective at much lower frequencies i think it may also be tuned to the frequency used although im not sure, i know if you remove it or if it becomes damaged (dirt such as fat acumaleted on it can become hot and melt it) a heck of a lot of microwave energy can escape, the gap arond the door is plenty long enough to let 433 mhz out, maybe if you want to improve it you could add the metalic springy contact sealing strip used on case joints to seal agaisnt emi to the oven door, although its not worth risking tampering with a microwave oven if theres any chance its liklely to be used again. i used to work on some of the first electronic controlers for microwave ovens. the radiation outside the ovens we were using at moderate distance was actualy remarkably low, we did have some problems inside the case with pcb tracks on some models wich just hapened to be just the right length to act as tuned anteneas tho.

I would sugest an ordinary metal instrument case would be better.

Colin =^.^=

Reply to
colin

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