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Magneto Noise

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jluckey(at)pacbell.net
Guest

Posted: Sun Apr 06, 2014 9:05 am Post subject: Magneto Noise

I flew w/ a friend recently and when trying to get awos for our destination airport (which is a pretty weak signal) it was almost impossible to hear due to magneto noise.  The radio is a Garmin 430W in a Cherokee and we were around 10 miles from the airport.  When we got within 3 or 4 miles the signal was much clearer.  All other transmissions with ATC & towers were acceptable but I noticed at high volume I could clearly hear magneto noise in the background.



I'm wondering if that's just the way it is or if there is a problem with the magnetos or P lead wiring.



There must be one of Bob's handy-dandy write-ups on this topic but a quick search of AeroElectric.com was in vain.

Can someone point me in the right direction?

TIA,

-Jeff

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tim2542(at)sbcglobal.net
Guest

Posted: Sun Apr 06, 2014 11:14 am Post subject: Magneto Noise

Not normal. Does it go away when you switch either mag off? YOu sure its a mag?

Tim





        From: Jeff Luckey <jluckey(at)pacbell.net>

 To: "aeroelectric-list(at)matronics.com" <aeroelectric-list(at)matronics.com> 

 Sent: Sunday, April 6, 2014 10:04 AM

 Subject: AeroElectric-List: Magneto Noise

  

 

I flew w/ a friend recently and when trying to get awos for our destination airport (which is a pretty weak signal) it was almost impossible to hear due to magneto noise.  The radio is a Garmin 430W in a Cherokee and we were around 10 miles from the airport.  When we got within 3 or 4 miles the signal was much clearer.  All other transmissions with ATC & towers were acceptable but I noticed at high volume I could clearly hear magneto noise in the background.



I'm wondering if that's just the way it is or if there is a problem with the magnetos or P lead wiring.



There must be one of Bob's handy-dandy write-ups on this topic but a quick search of AeroElectric.com was in vain.

Can someone point me in the right direction?

TIA,

-Jeff





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skywagon

Joined: 11 Feb 2006
Posts: 184

Posted: Sun Apr 06, 2014 12:01 pm Post subject: Magneto Noise

I would suspect the "shield" part of the P-lead cable has  broken and is no longer grounded at the mag. housing.  2nd, a small  chance that the heavy grounding cable from the engine to aircraft frame is  missing or not making a full connection due to corrosion or other  flaw.

 Dave

  

   

 [quote]   ---

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 08, 2014 7:08 am Post subject: Magneto Noise

At 12:04 PM 4/6/2014, you wrote:



I flew w/ a friend recently and when trying to get awos for our 

destination airport (which is a pretty weak signal) it was almost 

impossible to hear due to magneto noise.  The radio is a Garmin 430W 

in a Cherokee and we were around 10 miles from the airport.  When we 

got within 3 or 4 miles the signal was much clearer.  All other 

transmissions with ATC & towers were acceptable but I noticed at high 

volume I could clearly hear magneto noise in the background.



I'm wondering if that's just the way it is or if there is a problem 

with the magnetos or P lead wiring.



    Was this a new condition or has it been that

    way 'forever'. It's difficult for the neophyte

    observer to tell the difference between ignition

    noises getting into the system by way of plug wire

    radiation versus p-lead radiation.



    First, make sure that the perceived noise goes up

    and down with volume control settings on radio.

    This all but guarantees that it's coming in through

    the antenna.



    Then, disconnect both p-leads from the back of the

    magnetos and run the engine. See if the noise is

    still heard . . . turn to unused frequency . . .

    open squelch.



    If you can still hear it, then look for bad plug

    wire. If not, hook up one p-lead at a time and

    repeat experiment . . . see if noise is predicated

    on either or both of the p-leads being hooked up.



    Once you've identified the offending radiator,

    you need to figure out why. If this is a 'new'

    condition, then you're looking for something that

    has changed. Bad cap in mag (probably not both)

    broken ground lead on p-lead shield. If possible/

    practical wire p-lead wires per Figure Z-27



http://tinyurl.com/n3oy37f



    Ground p-lead shields at magneto end only . . .

    use p-lead shields to ground mag switch. Remove

    and existing ground to the mag switch.



    If the noise is coming from both p-leads,

    there are 'approved' magneto noise filters



http://tinyurl.com/l3s4mrj



    that most mechanics will install with a simple

    log-book entry.



    Bob . . .

   Bob . . .

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