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Help needed: continued strobe noise &

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nuckollsr(at)cox.net
Guest

Posted: Mon Jul 17, 2006 12:02 pm Post subject: Help needed: continued strobe noise &

At 06:37 AM 7/17/2006 -0400, you wrote:

 	  Quote: 	

In a message dated 7/16/06 8:11:43 AM Eastern Daylight Time,

luckymacy(at)comcast.net writes:

 > Lucky:  I used Van's pre-made wiring kit but I don't recall if the wiring

to

 > the strobes was shielded or not.

======================================

Lucky:

I think you found the problem.  I say that because of the above statement

about the pre-made harness.  If they are running the strobe's wires right 

along

side the wires for your other lights AND if they are not shielded then it 

would

be very easy for the other wires to pick up the noise from the strobes.

Try running a separate SHIELDED pair of wires and ground the shield ONLY at

the strobe.  The shielded pair should have three wires ... B+. Neg and 

SHIELD.

The Neg is grounded at both ends, while the shield is only at the strobe.  I

would still use the filter, just for S&Gs.  Run the strobe wires away from 

the

other wires.

I have a similar strobe system as you with the power supplies.  The strobes

mounted at the wing tips and tail; three power supplies.  I found that 

there is

a small amount of noise from the tail strobe.  I know I can get rid of it

with an RS type filter, but it is on a GA aircraft so I'm not allowed to 

use RS

or Lowe's aviation components 

You did say you tried mounting the filter at each location, Strobe and Radio.

  Another thing to check and I have not seen it mentioned is LEAD 

 LENGTH.  You

must keep the leads as short as possible between the filter and the strobe.

Still another trick you may want to try is to install a ferrite bead

(tolroid) on the B+ lead, close to the strobe.

Me still being a bit redundant, make sure you have extra clean ground

connections; aluminum is not a good material for electrical connections.

Well, beyond all the techniques and trick I mentioned in this post and my

other.  My other offer would be ... Where are you located, maybe we could 

meet

up?  I'd bet dollars to doughnuts I can solve your problem.  I'd be glad 

to help.

Barry

    What is the nature of the noise? Whine from the power supply or

    "popping" when the tubes fire? Have any noise isolation experiments

    described in chapter 16 been conducted?

    Bob . . .

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nuckollsr(at)cox.net
Guest

Posted: Fri Jul 21, 2006 6:37 am Post subject: Help needed: continued strobe noise &

 	  Quote: 	
		  As for Inductive / capacitive coupling.  We are talking DC circuits with 

Noise in the AUDIO frequency range.

As the saying goes: K.I.S.S. M.E. All this stuff about capacitive and 

inductive coupling is not an issue in a simple noise problem as we are 

discussing here.  AND what the heck is "NON-MAGNETIC BRAID-TYPE 

SHIELDING"?  Do you really expect people to go out looking for 

"mu-metal"?  ALL the braid used on any electrical circuit on our planes is 

NONMAGNETIC ... It is made of COPPER WIRE.  Copper is non magnetic the 

last time I checked.  Again K.I.S.S. M.E. is the word of the day.



Electronics is simple, it is really!  All these boog-a-boo statements only 

confuses the non-electrical types amongst us.  The only thing they need to 

know is how to remove the noise.  Again that goes back to the basics of 

noise, and breaking it down into DC and AC ... AC goes one step further 

(Audio Frequencies [AF] and Radio Frequencies [RF]).

Basics:

AF Noise - Shield and Ground at the source [This is why the Mic & Phone 

lines use insulating washers at the jacks and ground at the audio panel or 

radios.]

RF Noise - Shield and Ground at both ends.  [Here is where exceptions come 

into play - Some times the grounding is done through a capacitor.  BUT we 

are dealing with AF Noise not RF so I'm not going to try to confuse people 

out there.]

Let the manufacture of the wire worry about resistance of 1000 Ft and the 

capacitive coupling / inductive coupling at AF & RF.  The ONLY thing that 

would be of interest to our noise plagued brevien is the Percentage of 

Braid.  You did not say anything about that!  Yet again as long as you use 

Mil-Spec wire the percentage of braid is acceptable and again our brevien 

does not have to be concerned.



As for the Separation of wires .... I did address that with my very first 

statement to Lucky; read above.



I would suggest that all the AF noise (strobe noise) we are discussing be 

approached as I described AND then if the noise still exists just add 

another ground t=at the other end of the shield.  It is MUCH easier to ADD 

a ground than to remove a ground.


	


    The usefulness of shielding for wires is limited

    and there are no fixed rules for grounding this end

    or grounding that end. Further, shielding is a poor

    substitute for internal filtering when radio frequencies

    are involved.



    Percentage of braid is an exceedingly tiny concern

    and the use of "mil spec" wire is not a golden recipe

    for success. If one has a noise problem the first

    task is to properly identify the noise source and the

    nature of the noise. The the game of Clue is played

    to deduce the propagation mode. Fortunately with

    strobe systems, millions have been installed in as

    many vehicles with no noise issues. Similarly, thousands

    of system with noise issues have been successfully

    solved by application of very simple techniques . . .

    techniques that almost never involve departure from the installation

    instructions. If a noise problem is EVER mitigated by the

    repositioning of wires, this is prima facie evidence of

    a core problem wherein repositioning of wires only makes

    the symptoms go away and does nothing to fix the real

    issue.  Similarly, if a system that has worked successfully

    in many other installations suddenly seems to benefit from the

    addition of wire shields, that too is only an aspirin on

    the hurt that does not cure the infection.



    In my whole career, I've never found it useful to add

    shielding or to reposition equipment or its wiring as

    a means for improving performance. If the original

    poster of the problem can describe the results of any

    experiments described in the 'Connection (or elsewhere)

    to identify the propagation mode, then remedies are

    readily at-hand to break that mode.



    Bob . . .

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nuckollsr(at)cox.net
Guest

Posted: Fri Jul 21, 2006 7:02 am Post subject: Help needed: continued strobe noise &

At 01:54 AM 7/16/2006 +0000, you wrote:



 	  Quote: 	
		  



I have two "comm" issues that I haven't  been able to debug to completion 

yet.  I'm using an Xcom 760 radio with their pre-made harness.



1) I still hear my strobes in my headset even when they are grounded with 

the radio ground and even when I put power noise filters on.  However, the 

Radio Shack noise filters reference on Bob's web site were reported to me 

to be no longer carried by them.  So I used the only ones I could find 

locally which were sold by Pep Boys and the capacitor was 4700 uF instead 

of 2200 uF like Radio Shack apparently was.


	


    Okay, I found the data I was looking for in my post of

    a few minutes ago.



 	  Quote: 	
		  More specifically, the strobe noise is relatively faint until I select the 

Push to Talk button.  Then it gets pretty loud.  Some feedback going on 

there.  Looking for ideas from this list.


	


    Have you tried operating strobes from a separate

    battery? What is the nature of the noise you are hearing?

    "POP" or "whine"?

 	  Quote: 	
		  Should the capacitor specs have made a big difference on the effectiveness 

overall of the noise filter?  It made no measurable difference regardless 

of whether I installed it just before the radio or out at the strobe's 

power supply just before the AC +14v entered the power supply.  I even 

reversed direction of the filter and it didn't matter one iota.  Really 

bummed out about this turn of events since I thought they'd at least have 

made some observable difference based upon stuff in the archives.


	


    Your shooting in the dark. The task is to identify

    the propagation mode and THEN go after the fix.

 	  Quote: 	
		  2)  The second overall problem is that the radio still is reported to me 

by other pilots as weak when I get much beyond a couple of miles and 

breaks up in the pattern a lot.  I'm guessing it's because I can't put out 

enough consistent power to break their squelch consistently.  When on the 

actual ground taxiing around, if there's a crown or "hill" between me and 

another airplane on the ground forget it.  They can't hear me or vice  a versa.



When I check my radio with a handheld on the ground I seem to be just fine 

for the relatively close distances I've tried even when the plane is 

inside an open hangar and come in just as loud on the hand held as anyone 

else is.  It also doesn't matter whether or not the strobes are powered on 

or not as far as whether or not the range/strength improves.  ie, even 

with them off the lack of range doesn't improve.



I swapped the cable between the radio and the antenna and it made no 

difference.  I bought my antenna from Van's  but didn't do any kind of 

post install test besides checking it out with my comm radio and a hand 

held and it seemed fine at the time...



Instead of using RG-58 I bought two pre-made RG-400 cables.  What should 

the center conductor's resistance read end to end?  ~58 Ohms, right? My 

actual reading bounces all over the place no matter how stable I am in 

trying to read it. Strange.   Also, there doesn't seem to be a short 

between the center conductor and the plug itself when I check it with a 

multimeter so I'm guessing the plugs were installed correctly.



Things I have left to try is just buy a pre-made 12' RG-58 cable from 

radio shack and try it instead of the RG-400 cables.  Also, I don't have a 

spare comm antenna but I think RS carries a replacement 800 Mhz scanner 

antenna with the right BNC connector that I can just temporarily use just 

to see if makes any difference at all.



Any ideas from the list?


	


   What you're suffering from is a huge lack of data. A wise

   fellow once noted . . .



   "I often say that when you can measure what

   you are speaking about, and express it in numbers, you know

   something about it; but when you cannot measure it, when

   you cannot express it in numbers, your knowledge is of a meagre

   and unsatisfactory kind; it may be the beginning of knowledge,

   but you have scarcely in your thoughts advanced to the state

   of Science, whatever the matter may be. - Lord Kelvin"



   Your cited symptoms suggest low output power output. Get a

   wattmeter from a local two-way or avionics shop and MEASURE

   your radio's power output as-installed in the airplane.

   Measure it first with a dummy load . . . see:



http://www.aeroelectric.com/Pictures/Tools/Bird_43.jpg



http://www.aeroelectric.com/Pictures/Tools/DummyLoad.jpg



   then measure power output and MEASURE SWR with the antenna

   connected.



   Once you have the data from this exercise, we're then

   in a position give you good advice.



   I fully understand the difficulties of the task. One of

   the hardest things to do is get somebody to load/rent

   their tools. However, failing to apply the optimum tool

   oft leads to hours of experiments that gather no

   measurements that demonstrate movements toward or away

   from success.  Lord Kelvin had it down pat.



   Bob . . .

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FLYaDIVE(at)aol.com
Guest

Posted: Fri Jul 21, 2006 11:01 am Post subject: Help needed: continued strobe noise &

In a message dated 7/21/06 10:42:50 AM Eastern Daylight Time, 

nuckollsr(at)cox.net writes:



 	  Quote: 	
		       The usefulness of shielding for wires is limited

      and there are no fixed rules for grounding this end

      or grounding that end. Further, shielding is a poor

      substitute for internal filtering when radio frequencies

      are involved.

  

      Percentage of braid is an exceedingly tiny concern

      and the use of "mil spec" wire is not a golden recipe

      for success. If one has a noise problem the first

      task is to properly identify the noise source and the

      nature of the noise. The the game of Clue is played

      to deduce the propagation mode. Fortunately with

      strobe systems, millions have been installed in as

      many vehicles with no noise issues. Similarly, thousands

      of system with noise issues have been successfully

      solved by application of very simple techniques . . .

      techniques that almost never involve departure from the installation

      instructions. If a noise problem is EVER mitigated by the

      repositioning of wires, this is prima facie evidence of

      a core problem wherein repositioning of wires only makes

      the symptoms go away and does nothing to fix the real

      issue.  Similarly, if a system that has worked successfully

      in many other installations suddenly seems to benefit from the

      addition of wire shields, that too is only an aspirin on

      the hurt that does not cure the infection.

  

      In my whole career, I've never found it useful to add

      shielding or to reposition equipment or its wiring as

      a means for improving performance. If the original

      poster of the problem can describe the results of any

      experiments described in the 'Connection (or elsewhere)

      to identify the propagation mode, then remedies are

      readily at-hand to break that mode.

  

      Bob . . .

  

================================
	


Thank you Bob!



That is exactly what I said.  As the saying goes you do not have to reinvent 

the wheel.



Start with the basics and work from there.  The original post by this fellow 

contained information that he tried to obtain the Radio Shack noise filter ... 

And I must say they surely do work.  He did not have success getting it but 

did obtain a second brand.  He did not have any luck with that filter.  What 

should he do?  Start with the basics and work from there.



I have found just the opposite from you ... I have done at least 4 planes 

where repositioning the wires and/or running shielded wire have made a great 

improvement, or totally eliminated the problem.  Other things I do after the 

basics are Filters, Tolroid Cores, Feed Through Capacitors, Capacitors to Ground 

and Shorten wire leads.  Sometimes one arrow does not kill the Sphinx.  And I 

still have not used all my arrows.  One step at a time, starting with the basics 

as you said... Good installation practices.

I have always said ... YELLED about improving GROUNDS and connections.  Ya 

gots ta start somewhere ... Starts wit da basics.

----------------------------------------------------------------

Actually I thought this issue was dead ... Well, at least the horse did not 

move.

Barry

"Chop'd Liver"

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sat Jul 22, 2006 6:57 am Post subject: Re: Help needed: continued strobe noise &

I say ditto to Bob N's posting on this. 



I would like to add that a recent EDN article says some relevant stuff (but mostly PCB related..but electrons don't know the difference). Worth a look:

http://www.edn.com/article/CA6335295.html

Hidden schematic---Ground is a good place to grow potatoes and carrots.



It is often asked "If my 1972 Cessna didn't need all this EMI stuff...why do I need it now?" We live in a world where voltages are going down, frequencies are going up and the average airplane has 100,000,000 X as many transistors as your Cessna did. Otis Elevator tests to make sure that passengers' cellphones don't plunge their computer-controlled elevators into the netherworld. Good design practices can help and ultimately great simplifications will make this design process smoother.



"philosopher" --n. A lunatic who can analyze his delusions.

				- Ambrose Bierce

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

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