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Preventing RF Noise Pollution

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JLuckey(at)pacbell.net
Guest

Posted: Tue Oct 30, 2012 9:39 am Post subject: Preventing RF Noise Pollution

All,



I want to put a device which contains a micro-controller clocked (at) 1 MHz in

my RV-7.  I want it to be a good electronic citizen in the electromagnetic

village of my electrical system. (I don't want it to annoy its neighbors)



I'm looking for guidelines on how to prevent the device from introducing

noise back thru its power feed line.  Can I put a filter on the circuit

board on the incoming power line?  There is a 5v regulator - are those

devices noisy?



In an effort to reduce radiated noise, it is enclosed in an aluminum box

that seals well.



There is also control wiring that must travel thru the airframe.  Should

those wires have some kind of filtering on them as well?  Some of the

external wires are sensing remote analog voltages.  Do they need protection

also?



TIA,



Jeff Luckey

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 30, 2012 1:37 pm Post subject: Preventing RF Noise Pollution

At 01:36 PM 10/30/2012, you wrote:




All,



I want to put a device which contains a micro-controller clocked (at) 1 MHz in

my RV-7.  I want it to be a good electronic citizen in the electromagnetic

village of my electrical system. (I don't want it to annoy its neighbors)



I'm looking for guidelines on how to prevent the device from introducing

noise back thru its power feed line.  Can I put a filter on the circuit

board on the incoming power line?  There is a 5v regulator - are those

devices noisy?



In an effort to reduce radiated noise, it is enclosed in an aluminum box

that seals well.



   #1 rule, make the board layout tight. Make use of a

   ground plane if you can. Self contained uC devices

   have VERY tiny radiation apertures and few external

   leads (oscillator) that carry fast rise, potentially

   antagonistic signals.



There is also control wiring that must travel thru the airframe.  Should

those wires have some kind of filtering on them as well?  Some of the

external wires are sensing remote analog voltages.  Do they need protection

also?



   Generally not for RF. Your control and analog lines will

   generally benefit from some form of level shifting and/or

   filtering for input transient immunity . . . this same

   network wipes out the RF issues too.



   Power inputs for small circuits are also benign. You'll

   no doubt be using a linear regulator which, along with

   it's standard line capacitors, is a strong attenuator

   of RF.



   Small devices like this are seldom an radiated

   or conducted EMI concern. Your biggest integration

   concerns are for protecing the uC from outside

   stresses (Mil-Std-704 DC power and static discharges

   for handling).



   Send me a copy of your schematic and I'll suggest

   i/o conditioning networks.

   Bob . . .

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JLuckey(at)pacbell.net
Guest

Posted: Wed Oct 31, 2012 7:41 am Post subject: Preventing RF Noise Pollution

Bob,



Thanks for the pointers.  When I get closer to PCB fabrication, I may take

you up on your generous offer.



-Jeff



--

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