- To: Clinton <cgaddes@xxxxxxxxxxxxxxxxxxx>
- Subject: Re: [SLUG] EMF IPAQ
- From: Richard Neal <linuser@xxxxxxxxxx>
- Date: Sat, 14 May 2005 14:42:48 +1000
- Cc: 'SLUG' <slug@xxxxxxxxxxx>
OK, EMF interference needs a device that sends out the EMF and a receiving device with an antenna and the solid state interface that can translate said noise (not always but were keeping it simple here). The antenna can be a long track inside the device or a poorly shielded/filtered cable.
The problem here isn't the PDA but poor design when it comes to the device receiving the interference, in that it hasn't been designed to filter out outside EMF interference.
Now there are a few ways of getting rid of EMF:
A. This can be a simple piece of cardboard coated with a metal shielding layer (sometime they have plastic versions too) thats connected to earth (can be commons earth or Power Supply earth).
B. if the antenna is a cable then you can use a shielded cable.
A. The most common method of filtering is using caps (capacitors) Ive personally found a small 470pF cap wired between the antenna and earth to be very good at removing TV and Radio (FM not AM) from devices.
B. The second most common method is using ferrous beads around the cable or dissecting the track thats the antenna.
C. Just a note here if the interference is AM in nature I find common mode chokes to be the best and should be stuck usually on the PCP (or near it) were the antenna cable enters the product.
You can make a claytons shield for the PDA from a piece of cardboard ie page divider in a folder, and some tin foil (yep same stuff as used to roast a chicken). Glue the tin foil to the cardboard wait for it to dry, you then need to either solder or crimp a wire to the foil and run the wire to the earth or negative terminal of the power or battery (power is better). Place the claytons shield behind the PDA you can use some rubber bands to hold it in place(as close as possible to the case) that should work.
Beware any holes in the shield even though small are twice the area when it comes to calculating EMF. Yes so a 4cm square hole is 8cm in EMF terms pretty much making the shield useless.
It's funny in Europe they now have some very high standards when it comes to electrical devices were the standards stop companies selling devices or electrical equipment that can pick up things like mobile phone EMF noise or silly things like blue tooth headsets making your computer or TV go mental.
Reason I know about all this is because the company I work for designs equipment for sale locally and in Europe, and many competing products on sale here "cheaper" than what we sell can't be sold in Europe because they wont pass the EMF interference testing. Its very annoying trying to explain to a customer why its more expensive, until said customer has the joy of having there equipment go south on them because someone decided to pick up a mobile phone call 5 meters away.
Ever listened to a live radio or TV interview and right in the middle there this weird buzzing noise in the audio......yep the journalist in question just bought a cheap audio recorder with poor EMF filtering and someone has just taken a call on his mobile near by, always makes me laugh when it happens, it shows how tight some people/companies are.
Sorry for gabbing on but I know this will hit google and someone might like the extra knowlege.
On Fri, 2005-05-13 at 19:58, Clinton wrote:
Anyone no a good way to protect electrical equipment from EMF?
I have a IPAQ that need to site very close to a scanner that generates and
EMF to read RFIDS?
Any help would be welcomed?
Kryten Cat: "Hey, I got it! We laser our way through!?"
Kryten: "Ah, an excellent suggestion, Sir, with just two minor drawbacks. One, we don't have a power source for the lasers, and two, we don't have any lasers."
- Cat and Kryten, White Hole ( Red Dwarf )
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