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noise filter

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Mon Jun 07, 2010 6:37 am Post subject: noise filter

After following the link in Bob's posting to the center-fed half-wave antenna, I noticed that Miracle Antenna also sells an electrical noise filter.

http://miracleantenna.com/Smoothie.htm

Assuming the product performs as advertised, is it a useful product that is worth the time, money and weight penalty?  I seem to remember Bob saying that modern avionics should be designed to withstand any voltage variations that the aircraft throws at them.  Theoretically a pure DC supply voltage is better.  But practically speaking, is the average unfiltered aircraft DC bus voltage good enough?

  The Rotax alternator is single phase.  Its rectified output is not as smooth as that from 3 phase alternators.  Would a noise filter be beneficial for smoothing the output of a single phase alternator or is the output good enough without a filter?

Thanks, Joe

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
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Posted: Mon Jun 07, 2010 9:30 am Post subject: noise filter

At 09:37 AM 6/7/2010, you wrote:

 	  Quote: 	
		  



After following the link in Bob's posting to the center-fed 

half-wave antenna, I noticed that Miracle Antenna also sells an 

electrical noise filter.

http://miracleantenna.com/Smoothie.htm

Assuming the product performs as advertised, is it a useful product 

that is worth the time, money and weight penalty?  I seem to 

remember Bob saying that modern avionics should be designed to 

withstand any voltage variations that the aircraft throws at 

them.  Theoretically a pure DC supply voltage is better.  But 

practically speaking, is the average unfiltered aircraft DC bus 

voltage good enough?


	


     Yes.



 	  Quote: 	
		     The Rotax alternator is single phase.  Its rectified output is 

 not as smooth as that from 3 phase alternators.  Would a noise 

 filter be beneficial for smoothing the output of a single phase 

 alternator or is the output good enough without a filter?


	


     All potential victims of noise have a threshold

     above which the stimulus degrades performance. All

     potential antagonists for noise are never ZERO

     noise (although batteries ARE exceedingly quiet!).



     Successful integration of potential victims with

     potential antagonist requires a working knowledge

     of risk. There are agreements between users,

     manufacturers and regulators of products where

     a practical ability to WITHSTAND a certain amount

     of noise is tailored to a practical ability to

     LIMIT the noise generated.  Popular agreements

     include DO-160 and Mil-Std-704 . . .



http://www.aeroelectric.com/articles/Philosophy/Whats_all_this_DO160_Stuff_Anyhow.pdf



http://www.aeroelectric.com/Reference_Docs/Mil-Specs/Mil-Std-704f.pdf



     The rule of thumb for deciding whether or not

     to add extra-ordinary prophylactic measures

     against noise issues is to



     (1) search the current experience base and



     (2) wait and see.



     It MIGHT be that some single accessory you're considering

     for your project is extra sensitive to noise. Otherwise,

     don't start adding noise mitigation goodies to the

     system before you know that you truly have a noise

     problem THAT WAS NOT GENERATED BY IMPROPER

     INSTALLATION.

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Mon Jun 07, 2010 10:02 am Post subject: Re: noise filter

 	  Quote: 	
		  The rule of thumb for deciding whether or not

to add extra-ordinary prophylactic measures

against noise issues is to



(1) search the current experience base and



(2) wait and see. 	




Thanks Bob.  Good advice.  There is no sense fixing something that is not broken.

I will wait and see.

Joe

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_________________
Joe Gores

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