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Ignition noise in Jabiru engine.

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nuckollsr(at)cox.net
Guest

Posted: Thu Jan 18, 2007 8:31 am Post subject: Ignition noise in Jabiru engine.

At 10:07 AM 1/18/2007 -0500, you wrote:



 	  Quote: 	
		  

<dleonar1(at)maine.rr.com>



RE: the noisy ignition Jabiru.

http://www.aircraftspruce.com/catalog/eppages/magnetofilter.php

My Viking / Continental/ Bendix mags was noisy unitil I installed these

capacitors in the P leads. Then it stopped.  I really don't know enough

about it to explain the mechanics of this, but it definitely took the noise

out of the audio.  I assume the Jabiru mags have a p- lead somewhere, is

there any kind of filter on it?


	


    The way to confirm whether or not the p-leads are

    contributing to the noise is to simply disconnect them

    at the mags and run the engine. A wire that is NOT connected

    cannot conduct or radiate noise.



    If the noise goes away, then try wiring the mags as shown

    in Figure Z-26 and Z-27. Note that shields for p-lead are

    grounded to the ENGINE end only while the same shields

    PROVIDE GROUND for the ignition switch.



    If the noise comes back in spite of this treatment of shields,

    then a p-lead filter is in order.

 	  Quote: 	
		  I'm sure one of the geniuses ( my boss used to call us F*****g geniuses), on

this list can find you a $.97 Cap that will do the job, I'm ashamed to say I

paid $35.00 each for thes for my certified bird.


	


    P-leads are connected across the magneto's timing

    points which already has a high quality capacitor

    tied across it. An on-purpose filter for the purpose

    of attenuating noises conducted out of the mags on

    p-leads would be a combination of inductance and some

    SMALLER value of capacitance than what already exists

    inside the mag. It's more than a $.97 capacitor.

 	  Quote: 	
		  Are the Ignition wires shielded style?  I was told by an avionics guy ( King

factory type years ago) that a small amount of extra resistance in an old

plug wire , or a bad shield will make it noisy as well.


	


    Loss of shielding on a plug wire demonstrated to benefit

    by shielding is a potential threat against electromagnetic

    order. However, "resistances" in plug wires is another

    matter. It was discovered over 70 years ago that much

    radiated ignition noise from plug wires was a function of

    the wire's efficiency as an antenna. Solid copper conductors

    were much better radiators when circuit losses were low

    a radio frequencies.



    Predecessors to the modern EMC facility like the one

    shown here . . .



http://www.aeroelectric.com/Pictures/Misc/Screen_Room_circa_1935.jpg



    . . . were used to explore the effectiveness of various

    noise mitigation techniques. It was discovered back then

    that adding resistance in moderate amounts had little

    effect on spark performance but a lot of effect in

    killing the plug wire's efficiency as a radiator of

    energy. Autolite, AC and others offered "resistor plugs"

    with devices built into the assembly for the purpose of

    reducing noise. Later, resistance wire replaced the

    resistance plug . . . better to have the losses distributed

    over the length of the wire as opposed to concentrated at

    one end.



    Bob . . .

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icubob(at)newnorth.net
Guest

Posted: Thu Jan 18, 2007 7:32 pm Post subject: Ignition noise in Jabiru engine.

bob,

 let me talk thru this and see if i have it right as i have questions about 

this. wires that ground the jab coils at the ignition switch are shielded. 

this shielding is grounded at the engine end of the shielding . this 

shielding is used at the ignition switch to ground the switch. the shield is 

attached at the switch where you would attach a wire to ground the switch. 

this shielding is providing the same ground to the switch as if the switch 

had been attached to a negative ''forest of tabs''. have i got all this 

right?  thanks for yourhelp, bob noffs

---

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DonC

Joined: 18 Jan 2007
Posts: 1
Location: Western Aust

Posted: Thu Jan 18, 2007 10:30 pm Post subject: Re: Ignition noise in Jabiru engine.

This is my first post here - I just had to add to the comments about Jab ignition interference. I have a factory built J230 and since new I have experienced interference when receiving anything but strong signals - no problem with transmissions , only reception.

I changed to resistor plugs and they made a slight difference. one thing I cannot understand is when receiving a weak station and I turn the right mag off the noise all but disappears and the signal doubles in strength!!

Turning off left mag makes no difference. I have swapped coils from side to side , checked dizzy caps and rotors , fitted new ht leads ,all to no avail. As a last resort I am considering sheilding upper and lower cowls with adhesive aluminium foil and electricly bonding them to the firewall. Any suggestions please?

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jetboy

Joined: 22 Jul 2006
Posts: 233

Posted: Sat Jan 20, 2007 1:32 am Post subject: Re: Ignition noise in Jabiru engine.

You might like to check the thread at Yahoo



http://groups.yahoo.com/group/jabiruengines/message/16777



we have been testing inductive suppression HT leads and I have posted the radiated noise plots from the various types of HT leads in the files section.



Ralph

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_________________
Ralph - CH701 / 2200a

N81JG(at)aol.com
Guest

Posted: Sat Jan 20, 2007 10:35 am Post subject: Ignition noise in Jabiru engine.

I have had an ignition noise problem in my VariEze composite (very  susceptible since no metal frame to shield RF noise) plane since installing  a CD ignition form Lightspeed Engineering in place of one of the mags. I tried  the aluminum foil over the coil to plug leads grounded to the hex at the  plugs with no effect. After consultation with Klaus Savier at Lightspeed I  removed the foil and tightened the plug and coil clips and cleaned the  contact surfaces. That made a big improvement with my radio reception coming  through with only slight background plug firing noise. I am waiting for Klaus to  ship a set of plug leads with better wire and clips that should be even better.  Seems that any slight loose connection creates RF interference when the very  high voltage (40,000 volts plus) jumps the connection. I will make sure the  connections are tight and use a thin coat of dielectric grease (available  at auto parts stores as a Permatex product) on the connections. Hope  this will solve the problem. Be sure and check all your high voltage  connections.

  

 Good luck. I will report back if my changes work.

  

 John Greaves

 Redding, CA

 VariEze N81JG

  [quote][b]

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N81JG(at)aol.com
Guest

Posted: Sat Jan 20, 2007 10:54 am Post subject: Ignition noise in Jabiru engine.

Hi all,

  

 I forgot to mention that my VariEze has an O235 Lycoming with the CD  ignition and one mag. Didn't mean to confuse with the Jabiru, but ignition noise  is similar source from HT plug or coil leads.

  

 John Greaves

  [quote][b]

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paul.r.kuntz(at)gmail.com
Guest

Posted: Sat Jan 20, 2007 11:53 am Post subject: Ignition noise in Jabiru engine.

Regarding dielectric grease -- the dielectric adjective denotes the fact  that the grease does NOT conduct electricity.  Its use for electric  connections is to lubricate (which helps ensure that screw connections and  sliding connections mate completely and achieve the full metal-to-metal contact  desired), then after being displaced by the connecting process the grease keeps  oxygen away and helps prevent corrosion that can eventually break down the  connection.  The dielectric (non-conducting) property also prevents the  grease from forming a conductive pathway to adjacent circuits.  

  

 This isn't to say you shouldn't use it, particularly if Klaus recommends  it.  I'm not an expert on high-voltage applications, and Klaus has a lot of  practical experience.  Just trying to clarify and improve the underlying  knowledge base.

  

 Regards,

 Paul Kuntz

 Cozy MKIV and 

 Pipistrel Sinus 912 motorglider

 http://www.pipistrelbuilders.com/

 [quote]   ---

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