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Jabiru alternator noise

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ThomasTomlin(at)comcast.n
Guest

Posted: Fri Jan 13, 2006 5:43 pm Post subject: Jabiru alternator noise

Okay, I'll start a thread here.

I also elected to not be on the yahoo group so here goes.



I have a Kitfox Speedster with the Jabiru 3300 and a new Sensenich ground 

adjustable prop.



Currently I am hearing what appears to be alternator noise coming through my 

headset and

it is also being transmitted when I key the mike.



I have a capacitor on the output from the alternator and recently went to a 

newer one from

the Aeroelectrics supplier.



The noise is a high pitched whine at cruise rpm and the pitch changes up or 

down

with the throttle setting.  It is also only heard when pressing the PTT 

switch.



I have an alternator cut off switch and can turn off the alternator which 

eliminates the noise

when transmitting.



My headphone, PTT, and battery cables run parallel for about 3 feed, as my 

battery and headphone

jacks are behind me



I was hoping for an easier fix than rerouting the headphone/PTT wiring from 

behind me, and back up

to the panel.



Any thoughts?



Tom Tomlin

Kitfox IV

Greeley Colorado

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r_montagne(at)mac.com
Guest

Posted: Fri Jan 13, 2006 6:01 pm Post subject: Jabiru alternator noise

On 1/13/06 5:42 PM, "Tom Tomlin" <ThomasTomlin(at)comcast.net> wrote:



Hi Tom,



My comments below:



 	  Quote: 	
		   

 <ThomasTomlin(at)comcast.net>

 

 Okay, I'll start a thread here.

 I also elected to not be on the yahoo group so here goes.

 

 I have a Kitfox Speedster with the Jabiru 3300 and a new Sensenich ground

 adjustable prop.

 

 Currently I am hearing what appears to be alternator noise coming through my

 headset and

 it is also being transmitted when I key the mike.

 

 I have a capacitor on the output from the alternator and recently went to a

 newer one from

 the Aeroelectrics supplier.

 

 The noise is a high pitched whine at cruise rpm and the pitch changes up or

 down

 with the throttle setting.  It is also only heard when pressing the PTT

 switch.

 


	


A high pitch wine that tracks RPM is indicative of alternator/generator

noise.  When you key the transmitter you are increasing the load on the

electrical system.



A simple capacitor may not be adequate.  An 'L' network filter may be

required.  The 'L' is constructed by having an inductor between the

electrical source (alternator/generator) and the load (radios/avionics) in

combination with the capacitor between ground and the load end of the

inductor.  The purpose of the inductor is to provide a high impedance (i.e.

Resistance) to high frequencies (i.e. The A.C. Noise being carried on your

D.C. System in this instance) while the capacitor presents a low impedance

to the high frequency noise.  In essence this is a voltage divider where the

inductor has very low resistance at D.C. While the capacitor has high

(infinite) resistance at D.C. While the noise sees the high resistance of

the inductor at A.C. And low resistance of the capacitor.  The result is

that the D.C. Passes through the 'L' network with little or now attenuation

while the A.C. Passes through the 'L' network with a great deal of

attenuation.



If you only have a capacitor installed then the inductor is presenting very

low impedance/resistance at both D.C. And A.C.  This results in very little

attenuation of the A.C. Component.



'L' networks are sold for a variety of applications ranging from car stereos

to avionics/amateur radio equipment, etc.  The trick is getting an 'L'

network that is appropriately designed for the electrical load as you don't

want the inductor to generate a voltage drop under D.C. Load (which may

create a whole different set of issues).



I'd recommend installation of an 'L' network and checking that the ground

strapping is of good quality and sufficiently large for the task.



Best regards, Ray Montagne

Cupertino, CA



 	  Quote: 	
		   I have an alternator cut off switch and can turn off the alternator which

 eliminates the noise

 when transmitting.

 

 My headphone, PTT, and battery cables run parallel for about 3 feed, as my

 battery and headphone

 jacks are behind me

 

 I was hoping for an easier fix than rerouting the headphone/PTT wiring from

 behind me, and back up

 to the panel.

 

 Any thoughts?

 

 Tom Tomlin

 Kitfox IV

 Greeley Colorado

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