REFLECTOR: Ignition Noise

Wed Jun 13 18:17:26 CDT 2007

I can disconnect the antenna from the back of the 430, or disconnect at the wing - both cases the noise goes away.  If I connect the portable antenna with a length of RG58, I get the noise. If I take the rubber ducky antenna off the RG 58 the noise stops, so it is definitely coming in the receiver of the 430 and not getting trapped out like it does with the Microair.

Today I went up to the hangar to verify the grounding.  Sure enough, although my DVM shows a very low resistance, 0.1 ohm, it showed a 60 milivolt difference between battery ground and the 430's case or the ground bus which is next to it.  I cleaned terminals and got this down to 11 mv and I thought - OK this is it!  But cranked her up and still clicking - just keeps on clicking!

Tomorrow I am going to check grounds from nose to tail using Brian's suggestion - looking for voltage drops and trying to clean each one up.  I have improved one  problem - occasionally I would get a low voltage alarm -11.5 volts when the gear was being retracted.  Most of the time, voltage only drops a few tenths. 

Still looking!!!
Ronnie    

  ----- Original Message ----- 
  From: Michael Watson 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Wednesday, June 13, 2007 5:27 PM
  Subject: Re: REFLECTOR: Ignition Noise

  Hi Ron,

  I have been following this thread form the beginning,
  Your problem does not seem to be a power or ground
  induced noise. It seems that some harmonic of the noise
  frequency generated by your EIS, is being picked up by 
  your antenna  and the  430 ANL circuits is not filtering
  it out. ("IF I DISCONNECT THE COM ANTENNA, THE NOISE STOPS")
  Your Microair 760 may be cheaper but has a better ANL circuit.

  Where did you connect the portable antenna. directly to the rear of the radio,
  or the connector between the wing and strake ?

  I would contact Garmin and find out if there is any way to increase the
  sensitivity of their ANL circuit.

  On 6/13/07, Ron Brown < romott at roadrunner.com> wrote:

    I have resumarized the problem and trouble shooting to make the reading (and your suggestions easier):

    The PROBLEM: 

    Spark plug noise on the Garmin 430 audio out to the headphones.  No noise on the #2 COM which is a Microair 760.  Noise increases in frequency (twice engine RPM) as engine RPM is increased.  Noise goes away when the Jeff Rose Electroair Electronic Ignition system is turned off.  Noise also goes away when the COM antenna is disconnected from the Garmin 430.  The noise continues when the PS4000 Intercom/Audio panel is turned off.  The noise is also evident on the Garmin's NAV Audio.  Spark noise can be heard on a Radio Shack portable scanner.  The noise has been there for quite a while - but in the past it always improved after a few minutes to the point it was not a nuisance after a few minutes of running.  But now the noise is continuous.  By the way, the noise does not break the automatic squelch - but can be heard when a distant transmitter breaks squelch or the auto squelch turned off on the Garmin.

    Other info about the system.  Velocity with Lycoming IO 360 flying for 350 hours.  Slick magneto and Jeff Rose Electroair Electronic Ignition.  The ignition power goes down the right duct with the other noisy wires such as the 4 ga main feed to the starter and alternator and the copper ground tubing vacuum line .  My headphone connections are in the keel behind the seats.  The headset jacks are grounded only at the Audio Panel.  My antenna wires run down either side of the fuselage just above the floor ducts.

    All of my instrument panel grounds are to a single point - ground bus bar which is connected to the negative side of the battery.  The avionics are fed off an avionics bus which can be fed off of the main power bus or directly from the battery (an implementation of Nuckolls essential bus). There is a diode between the main bus and the essential bus which prevents the main bus from dragging down the essential bus.  

    The TROUBLESHOOTING:

      1.. Swapped COM Antennas, connected a portable antenna 
      2.. Swapped headphones. 
      3.. Installed balluns on the COM antenna wire. 
      4.. Swapped Garmin 430's with a friend. 
      5.. Installed new REM37BY Autolite spark plugs 
      6.. Installed new radio resistance spark plug wires from Electroair 
      7.. Powered the Garmin from a 2nd battery, installed a Radio Shack noise filter (choke and capacitor). 
      8.. Checked grounds (cleaned and retightened) at EI and central ground bus at instrument panel  
      9.. Checked grounds for the power going to the EI.  It was grounded on both ends, lifted the ground at the panel - no effect. 
      10.. Powered the EI via a twisted pair cable connected to a 2nd battery. 
      11.. Installed a Radio Shack noise filter (choke and capacitor) on the EI power input. 
      12.. Replaced the direct fire coils (NAPA IC39SB - same as used on Pontiac and Buick auto engines)         
      13.. removed the EI timing head so that I could spin it and make sparks while the engine was not running looking/listening for spark jumping anywhere, none found. 
      14.. Replaced one plug wire at a time then checked for noise while spinning timing head.  No change.
    I can't think of anything else to try other than replacing the EI with a Slick magneto - ain't going to happen!

    Any and all ideas WELCOMED!!!!

    THANKS!
    Ronnie Brown
    Velocity 173 Elite RG Lycoming IO360 

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  -- 
  Mike W.
  1997 Velocity Elite RG
  Franklin /IVO Electric CS 

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