VHF antenna location on m7 235 1986 alternator noise

[maulecan]

Hi every one!,My two nav com antennas are installed on top on leading
edge near the windshield,, and when see other maule pics the antennas
are more rear cabin on trailing edge of wings.
Maybe top front antennas give my radio noise trouble??
does anyone know diffenrence front or rear location rod.
tank you to help me!!

[a64pilot]

Front = old style, rear = new style. Only difference that I have been told is that wind noise is greater if antennas are located old style.

What kind of radio noise? Usually alternator is a whine, ignition is a tap, tap, strobes a ping type of noise.

[maulecan]

alternator noise more with engine rpm, when close alternator switch solve trouble.will check engine mount ground strap or other change alternator??? tank you! for answers.Christ

[a64pilot]

First check grounds, all grounds. If nothing else works, you may want to install a "noise filter" just a capacitor actually http://www.aircraftspruce.com/menus/el/ ... lters.html
But, I would first try to find and fix the problem rather than mask it.
It could be an alternator, not sure which component in an alternator goes bad that causes this, maybe diodes?
Most of my electrical problems usually end up being high resistance grounds.

[maulecan]

ok check all ground and i know my nav com antennas are not well
grounded are install in silicone and paint
may be trouble tanks

[maulecan]

All ground checked and rounting alternator wire with no succes.
Finaly install lonestar eliminator on nav com dc line and solve trouble
Supect My prestolite alternator or regulator,will go at alternator shop this summer.

[gbarrier]

Still fighting similar problem.

Have had bad alternator whine in the KX155 since purchasing airplane almost two years ago. I seldom use the King and there was no problem with the 430W I have slowly scratched my head and picked at it. Seems like recently I get a little static on lower frequencies on the Garmin but don't know if it is related since it is not really a whine like on the King.

First I took the alternator off for a look. Replaced short brushes and cleaned up slip ring. checked diodes and gave it a try. Nothing changed. I weathered the problem a while longer. I installed a big old Lone Star 70 amp filter only to find a similar unit already inline. No change. This week I removed the alternator again and replaced all of the diodes just to be sure. Obviously no change.

Then I found this article: http://www.avweb.com/news/maint/182896-1.html. Gave it a try and the noise which changes with rpm does increase considerably when I load the circuits up. If I am to believe this article the regulator is the culprit. There is also a capacitor hanging on the regulator which I have changed.

Sooo, has anyone experienced these symptoms? If so, did replacing the regulator fix the problem. Not above buying the Lone Star Eleminator to put inline with the avionics buss but would like to get to the root of the problem.

Also, does anyone have the part number for the Lamar regulator for the Prestolite/Electrosystems alternator on the 235. Perhaps I should start shopping.

[VA Maule]

Maule had the regulator in stock for mine, shiped it out the same day. Mine was the Electrosystems alternator.

[gbarrier]

Regulator on the way. Really hope that is the source. Guess the only other thing I could have tried was another KX155 but the noise did go away when I turned off the alternator and increased as I loaded it. Guess we'll know next week.

[captnkirk]

Gary Twin Lakes sent my kx155 to Chester for the overhaul came back good as new. I didn't have the noise just no range on the radio until it failed. The previous owner had replaced the regulator some time back. That had cleared up some of the noise he had. I heard the sun came out . Landed GSO this afternoon still overcast but some breaks.😉

[VA Maule]

Maulecan check the shielding on the coaxial cable, it should only be grounded at one end if ground is made in more than one place it can pickup chassis noise of which the alternater is the loudest. A small chafed spot on the cable can make that second ground.

[andy]

Gary, improving the antenna ground for the KX155 would be my first guess since the 430W isn't getting the noise. The KX155's squelch is probably set more sensitive than the Garmin. If the alternator or ACU is producing so much noise that it renders the inline filter ineffective, then you'd probably hear it in the intercom even when the KX155 is off the intercom circuit. You've probably already switched the KX155 audio off on the audio panel and verified that the alternator noise isn't coming from any other audio source on the intercom circuit. Another possibility is a loose headset jack nut on the panel, but I think you'd hear the noise even when the KX155 is off in that case.

I assume that the KX155 has a dedicated coaxial cable and antenna. Maybe there's a problem with one of them. I'd replace the coaxial cable and connectors before the antenna, but I've seen antennas create noise as they get older. If you have the ability to swap the comm antenna cables between the 430W and the KX155, that would eliminate that possibility.

[gbarrier]

Thanks Andy. I'll give it a shot when I get home Sunday.