Static on transmit

[Jr.CubBuilder]

My plane got a new alternator and motor, now there is a loud buzzing that seems to be in sync with motor RPM only when the field windings for the alternator are on and I push the transmit. When I turn the alternator off via the breaker switch for the field windings there is no buzz when I transmit with the motor running

I previously had an alternator on the previous motor, and origionaly had a generator when I first got the plane. I have never had this problem with either of the previous setups. The intercom and radio have not changed nor has my headset or intercom jack setup, however the mechanic has been rootin around behind the panel.

PM1000 intercom, KX170 Nav/Com

I'm thinking I've got a bad ground, but the buzz is only present when I transmit and the alternator is on. If it were a bad ground to the airframe I would think I'd hear all the time, unless the squelch is filtering out the noise(?)

Any ideas?

So far I haven't had a chance to talk to my old mechanic, the new one seems to think it isn't an issue.

 

[Greg Smith]

Any chance you got an alternator with a bad diode or armature winding? Also, is there adequate bonding between the alternator, engine, engine mount and fuselage?

 

[redrooster]

So Jr, is the 170/180 up? Tell us all about it........

Rooster

 

[Jr.CubBuilder]

So Jr, is the 170/180 up? Tell us all about it........

Rooster

Not yet, but it's almost done after some more paint and a valid weight/balance. I'm hoping next week, but then again I used to be hoping for before Christmas.

 

[mvivion]

Sounds like a stinker of an alternator to me.

MTV

 

[mike mcs repair]

This is probably overkill.... But......

My last resort way of finding/Identifing noise gremlins...

Being that the battery is the HUGE noise filter, any bad connections allow noise that normaly the battery will soak up and hide, to be heard....so long before adding a noise filter, or a new Alternator, i hunt for bad connections...

So to IDENTIFY the bad conection/noisy conection, or bad part... say like when chasing your alternator sounds

First use a temporary jumper wire from a case bolt of alternator to battery ground post, run-up test it... is sound still there? if it is gone the problem is in the ground circut, so move end of jumper that was at battery ground to next closer conection to alt (which is the other end of the battery - strap at this 2nd step).... and repeat this till you find it...

IF the above ground directly to battery terminal did NOT make it go away.....

Then do a temp jumper wire from alt output + terminal to battery positive terminal.......run-up test it... is sound still there? if it is gone it is in the positive side of alt output circuit, so move end of jumper that was at battery positive to next closer conection to alt (which is the other end of the battery + strap at this 2nd step).....and repeat this till you find it...

If all that did not work, then I might call it noisy alternator it self....

This method has worked for me on diffrent planes to find, bad master solinod, and a coroded conection on a alt out breaker when all else failed

mike