REFLECTOR: Intercom noise

Brian Michalk michalk at awpi.com
Thu Jan 6 09:23:03 CST 2011 

Ah.  First try running 1) without mags, then 2) without EI.  See if the 
noise goes away.  If the EI is the noisemaker, there's a couple of 
places that can cause problems.  Depending on the coupling mechanism, it 
can be RF radiated from the wires, or it could be voltage spikes on the 
power leads, or it could be a return path problem described earlier.  Is 
your EI a wasted spark setup (two plugs per pack)?

On 1/6/2011 8:39 AM, aminetech at bluefrog.com wrote:
> OK.  What about my EI? (auto wires)
>
> --- michalk at awpi.com wrote:
>
> From: Brian Michalk <michalk at awpi.com>
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Subject: Re: REFLECTOR: Intercom noise
> Date: Wed, 05 Jan 2011 21:16:26 -0600
>
> I forgot.  Aviation plug wires are shielded (providing their own 
> return path).  Check those for frayed ends.
>
> On 01/05/2011 08:38 PM, aminetech at bluefrog.com 
> <mailto:aminetech at bluefrog.com> wrote:
>
>
>
>     --- michalk at awpi.com <mailto:michalk at awpi.com> wrote:
>
>     From: Brian Michalk <michalk at awpi.com> <mailto:michalk at awpi.com>
>     To: Velocity Aircraft Owners and Builders list
>     <reflector at tvbf.org> <mailto:reflector at tvbf.org>
>     Subject: Re: REFLECTOR: Intercom noise
>     Date: Wed, 05 Jan 2011 20:13:00 -0600
>
>     Hmm.
>     if the shield is properly connected to the mag, it should be
>     catching any radiated electrical noise.  There are two possibilities.
>     1) the shield is not well connected
>     The shield that connects to the mag ground?  I cut the ends off
>     and put new ones on, so that's good.
>
>     2) the return path from the plugs-to-engine-to-magneto is not well
>     connected.
>     What is the engine-to-mag path?  I don't think I have one.  I'll
>     chech the resistance from mag case to engine.
>
>     In 1) the shield floats with the core conductor and radiates
>     In 2) the magneto case experiences a voltage differential
>     (relative to ground) because of high resistance in the return path
>     from the plug, causing the shield to radiate.
>
>     This is all assuming it's magneto noise.  If your test is positive
>     for magneto noise, then check for 1) or 2).
>
>     On 01/05/2011 07:43 PM, aminetech at bluefrog.com
>     <mailto:aminetech at bluefrog.com> wrote:
>
>
>
>         --- michalk at awpi.com <mailto:michalk at awpi.com> wrote:
>
>         From: Brian Michalk <michalk at awpi.com> <mailto:michalk at awpi.com>
>         To: Velocity Aircraft Owners and Builders list
>         <reflector at tvbf.org> <mailto:reflector at tvbf.org>
>         Subject: Re: REFLECTOR: Intercom noise
>         Date: Wed, 05 Jan 2011 18:54:08 -0600
>
>         Does the noise stop when that mag lead is grounded?
>         No.
>           What about when you disconnect the mag wire altogether?
>         Good idea.  I'll try that tomorrow.
>           Try easy tests first, don't try to fix anything yet.  Take
>         your hypothesis and test it.
>
>         Is it shielded twisted pair, or coax?
>         Coax
>           Does the mag P-lead return back to a ground at the mag(correct),
>         Yes
>          or through some other ground path(wrong)?
>
>         What is the frequency?  Mags will hum at 1/2 the RPM.
>         Probably 1/2 rpm, definitely not the alternator frequency.
>         John
>           an Alternator will hum at 3X of the alternator RPM, which is
>         several multiples above engine RPM.  Can you eliminate based
>         on that frequency?  If it's the alternator, disconnect battery
>         and field (or belt) and test again.  If it is the alternator,
>         do you have a ground strap from that case to your starter
>         ground cable ... or at least a very good confirmed electrical
>         connection?
>
>         On 01/05/2011 06:30 PM, aminetech at bluefrog.com
>         <mailto:aminetech at bluefrog.com> wrote:
>
>             I'm still trying to eliminate noise on my intercom.  It
>             occurs when the engine is running, even while starting. 
>             My mag wire going to the switch is in the overhead duct
>             along side the wires for the headset jacks.  Can this
>             close proximity be the problem?  The mag wire is shielded.
>             John
>
>             _______________________________________________
>             To change your email address, visithttp://www.tvbf.org/mailman/listinfo/reflector
>
>             Visit the gallery!www.tvbf.org/gallery  <http://www.tvbf.org/gallery>
>             user:pw = tvbf:jamaicangoose
>             Check new archives:www.tvbf.org/pipermail  <http://www.tvbf.org/pipermail>
>             Check old archives:http://www.tvbf.org/archives/velocity/maillist.html
>
>
>         _______________________________________________ To change your
>         email address, visit
>         http://www.tvbf.org/mailman/listinfo/reflector Visit the
>         gallery! www.tvbf.org/gallery <http://www.tvbf.org/gallery>
>         user:pw = tvbf:jamaicangoose Check new archives:
>         www.tvbf.org/pipermail <http://www.tvbf.org/pipermail> Check
>         old archives: http://www.tvbf.org/archives/velocity/maillist.html
>
>         _______________________________________________
>         To change your email address, visithttp://www.tvbf.org/mailman/listinfo/reflector
>
>         Visit the gallery!www.tvbf.org/gallery  <http://www.tvbf.org/gallery>
>         user:pw = tvbf:jamaicangoose
>         Check new archives:www.tvbf.org/pipermail  <http://www.tvbf.org/pipermail>
>         Check old archives:http://www.tvbf.org/archives/velocity/maillist.html
>
>
>     _______________________________________________ To change your
>     email address, visit
>     http://www.tvbf.org/mailman/listinfo/reflector Visit the gallery!
>     www.tvbf.org/gallery <http://www.tvbf.org/gallery> user:pw =
>     tvbf:jamaicangoose Check new archives: www.tvbf.org/pipermail
>     <http://www.tvbf.org/pipermail> Check old archives:
>     http://www.tvbf.org/archives/velocity/maillist.html
>
>     _______________________________________________
>     To change your email address, visithttp://www.tvbf.org/mailman/listinfo/reflector
>
>     Visit the gallery!www.tvbf.org/gallery  <http://www.tvbf.org/gallery>
>     user:pw = tvbf:jamaicangoose
>     Check new archives:www.tvbf.org/pipermail  <http://www.tvbf.org/pipermail>
>     Check old archives:http://www.tvbf.org/archives/velocity/maillist.html
>
>
> _______________________________________________ To change your email 
> address, visit http://www.tvbf.org/mailman/listinfo/reflector Visit 
> the gallery! www.tvbf.org/gallery user:pw = tvbf:jamaicangoose Check 
> new archives: www.tvbf.org/pipermail Check old archives: 
> http://www.tvbf.org/archives/velocity/maillist.html
>
>
> _______________________________________________
> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20110106/5a6a6d1c/attachment-0001.htm>

More information about the Reflector mailing list