Trouble-shooting engine noise

Hello,
I have the following issue with my radio/intercom system and I was hoping to get some suggestions here on how to trouble-shoot. I hope I can describe the issues clearly enough for you to help. If you need more info....let me know.

1.....With the engine OFF, everything works fine! The radio is crisp and clear and the intercom can be adjusted to perform as it is suppose to. I've transmitted to other aircraft flying overhead and they respond that my transmissions are very good and no static.

2.....With the engine RUNNING, the intercom cannot be adjusted to work properly. Either you hear a lot of noise and be able to talk, or don't hear anything and can't communicate over the intercom. Using the radio brings the following....when you use the PTT button, you hear a lot of noise. I'm able to transmit and receive ok and everyone says the radio sounds fine.

My opinion is that I have a lose connection someplace in the wiring. Does anyone have any suggestions on how to trouble-shoot this???

Steve

Paris12Man said:

Hello,
I have the following issue with my radio/intercom system and I was hoping to get some suggestions here on how to trouble-shoot. I hope I can describe the issues clearly enough for you to help. If you need more info....let me know.

1.....With the engine OFF, everything works fine! The radio is crisp and clear and the intercom can be adjusted to perform as it is suppose to. I've transmitted to other aircraft flying overhead and they respond that my transmissions are very good and no static.

2.....With the engine RUNNING, the intercom cannot be adjusted to work properly. Either you hear a lot of noise and be able to talk, or don't hear anything and can't communicate over the intercom. Using the radio brings the following....when you use the PTT button, you hear a lot of noise. I'm able to transmit and receive ok and everyone says the radio sounds fine.

My opinion is that I have a lose connection someplace in the wiring. Does anyone have any suggestions on how to trouble-shoot this???

Steve

Click to expand...

Steve,
Since your signiture says you have been flying for more than 80 hrs.
lets start with a simple question.

Has it worked well previously, and this is a recently new problem?

I believe I have always had an issue. Unfortunately, I've always flown by myself and never really used the intercom until recently. I also upgraded my headset to a ANR model and now I've begin noticing the "other" noises when flying.

Wind blowing on a microphone can make lots of noise. Is the passenger wearing the headset when you have a noise problem or is the headset lying on the seat? Try covering the mic with your hand to block the wind.
While on the ground, pull the fuel pump fuse to see if that makes a difference.
Try using different headsets.
Shut off the outside lights if they are on.
Try isolating the earphone jacks from the airframe using insulating washers similar to the mic jacks. Also isolate the tape recorder jack if you installed that. Insulating the audio jacks will require pulling new ground wires from the audio jacks to the intercom.
Good luck.
Joe Gores

Joe, since everything works fine while the engine is off, doesn't that show that the earphone jacks are okay? Noise only shows up when engine is running. During engine operation, I have shut off all electrical components in the past (not fuel pump) and noise is still there. I've tried two different models of headsets with a passenger on board during tests. Steve

Trouble shooting this type of problem via typed messages is difficult if not impossible, but here are a few things to consider.

The 403 intercom doesn't always play nice if you are connecting two different headsets to it. It is designed with a common audio channel and just a single squelch circuit, wich is meant for both headsets to be the same model. With different head sets it is often impossible to set the squelch level to work with both of them. Sometimes different headsets work ok togetehr, but often times they do not.

Good signal to noise ratio is critical. It is imperative that each mic be positioned as close to pilot and passengers mouth as possible. If not, it will produce the same problems as using different headsets. If you are using different headsets, and the mics are not properly positioned, you will have double the problems.

All of the RV-12's I have flown, have worked well with the volume and squelch both set at just slightly clockwise of the mid point of the control range.

I suggest you borrow two decent quality head sets of the same model (or a second one to match the new ANR you have), and try them out together with the mics placed as close to mouths as practical.

If performance is still poor, you will have to look a little deeper.

It is always possible that you have a bad intercom. The TeenFlight RV-12 had a problem with distorted/garbled intercom audio but radio transmissions sounded fine. The problem also effected the squelch adjustment, making it difficult to ever find a stable setting. Replacing the intercom totally resolved the problem.

since everything works fine while the engine is off, doesn't that show that the earphone jacks are okay?

Click to expand...

Well yes, the jacks are OK. The problem could be that the earphones are sharing the same conductor (airframe) as noise producing devices. When two or more electrical devices share the same conductor, it is possible for one device to effect another device. It is good practice to isolate headphone jacks from the airframe and connect them with discrete wires. I am not saying that doing that will solve the noise problem. But it is worth a try if all else fails.
The shield of the ignition switch wires should NOT be continuous from the engine to the instrument panel. Check to make sure the shield is grounded at the engine. See 46-12 figure 1.
Joe Gores

Scott has good advice, as usual.
Joe Gores

Resolved

I just wanted to close this thread and provide my resolution to the problem so others might benefit from my issue. As we know the SL40 has adjustments that you can make by entering the software by pressing the monitor button. One of the adjustments you can make is the "Sidetone value". The Sidetone value range is between 000 to 255. Mine was factory set at 128 which is way too high for both of my headset models. I reduced this value to 030 (just a wild shot) and took a short flight this afternoon and to my excitement the loud noise was gone when I keyed the mic. The Intercom issue was also resolved. I had to increase the value to 040 after communicating with another aircraft in the pattern, but other than that, life is once again wonderful!
Steve

I had the same problem after I installed the Skyview in New Blue. And after a lot of head scratchin' I finally did exactly what Steve did. If the sidetone level is set to zero in the SL-40, its volume will follow the volume knob. The higher the setting on the volume knob, the louder the sidetone. Get it off zero thru the SL-40 setup menu. I have New Blue's set at 15 and it it works just fine now.