Radio sttic and whine.

[Josh]

I am having some annoying noise coming through the radio system, I get a whining noise and static noise after about 10 minutes of flying and the noise changes pitch with different power settings. If I key the mike for one second the noise goes away then slowly starts building back up after about 5 minutes, If I hit the landing light or recycle power same thing, the noise goes away then slowly builds back up. I have an old Narco 250 and soft-com intercom. I have checked the antenna and all connections,changed headsets, cleaned headset plugs, maybe it is a bad alternator?

 

[teeweed]

Josh about a year ago I started hearing my strobe through my headsets. Soon after that my strobe went out. Sounds like your noise might be coming from the alternator. teeweed

 

[mghallen]

Sounds like some wiring wiring maybe, depending on the noise could be mag wiring also. By chance have you been flying in/near Kotzebue?

 

[irishfield]

Have you got a capacitor on the B lead of your alternator?

 

[Josh]

I will need to go look, but if I do have one should I check it with an Ohm meter and what should it read?

 

[teeweed]

One way to test your capacitor is to take it out and give it a few seconds on a 12 volt battery charger. Then lay it on the kitchen table and wait for your wife to pick it up and make connections with the wire and the case. When you hear a loud scream you know you have a good capacitor. teeweed

 

[mvivion]

Josh,

That sounds like a static issue. Static builds up on the airframe, and dissipates through the pointy parts--the antennas. Now you transmit, and that dissipates the charge.

You might try attaching a few static wicks and see if that helps. Cheap, and easy. If they don't work, you don't have a lot invested.

MTV

 

[bob turner]

If it were not for the slowly increasing bit, which indeed may be static buildup, I would suspect you lost one diode in your alternator. It will still charge, and run the system, but you will hear a whine related to engine RPM. Without the capacitor, the whine can be enough to overcome the radio. Pull the alternator off, have it checked, and inspect the mount.

 

[Clyde and Susan]

From your description it sounds to me like the noise is being caused by your generator/alternator only when it is producing little or no current. After start-up the battery is low and the alternator is producing current at the instructions of the regulator, as the battery comes back up to full charge, the regulator reduces the current output of the alternator and that's when the noise starts. If you do anything to draw current from the electrical system such as turning on the landing lights, the alternator produces more current and the noise goes away until the battery is replenished and then the noise starts again. All of this points squarely at the alternator. The suggestion of a possible bad diode is very likely the correct one. ...Clyde Davis