Avionics advice??

[tkatc]

My new RV7A has 2 icom a200 radios coupled with a Garmin 340 audio panel. I like the set up and it seems easy enough but ATC complains about garbled transmissions. I seem to receive them fine though. I use a halo and have checked the mic direction. I have read about grounds and antenna leads but have not really tested anything for lack of knowledge. I do get some strobe noise and a whine when I increase my panel dimmer light to higher intensity. Perhaps this is a symptom. I also noticed that when I select the pilot " isolate" feature to kill music on final, all the RF noise and whining goes away.

I feel like I am a bit lazy just asking questions without really investigating anything on my own but I don't really know where to begin....

So what would you suggest? Please include detailed instruction because I don't know much about radios except how to push the PTT.

 

[Ironflight]

What is your music source? If the whine goes away when you switch to "Isolate", then the music source is likley the issue. If you are using a 2,3,4-96, these are known to create groundloops when you plug in the audio cord to the panel. The 696 seems to have fixed this (mostly).

 

[tkatc]

The music source is Sirius radio. I believe the problem exists with or without the radio turned on. I only gave that example of the isolate button in an effort to pinpoint symptoms. I will check on the sirius radio but I doubt that is the cause.

I am using a gamin aera plugged into a 12 volt charge receptacle but I do not have it connected via the audio system in any way.

 

[dlloyd3]

radio noise

I also had good reception but got complaints on transmission. I tried several things without success. Finally got systematic about locating the source of noise. Transmit to someone and turn things off or on one at a time until you find the problem. Music, intercom, other radios, alternator and finally engine. Use another headset or mike jack. Is it on one frequency or several? I had my shielded p-leads bundled with other wires coming thru the firewall and apparently caused my problem.

 

[David_Nelson]

I also noticed that when I select the pilot " isolate" feature to kill music on final, all the RF noise and whining goes away.

Hi Tony,

You didn't specify if going to 'isolate' also cleared up your transmissions. Did it?

Also, are the audio jacks truly isolated from the air-frame? Using a PSE-8000B (which is compatible to the GMA-340 so I would expect the same behavior), check that the outer portions of your audio jack(s) are not grounded to the air frame using a VOM (volt-ohm-meter). If you don't know how to use a VOM, find somebody on your field to show you - very valuable tool and very easy to use.

If they are touching the air frame, this may be the cause. I "borrowed" an idea from IronFlight on using very small plastic snap bushings and trimming/cutting them down to make some isolation washers.

Good luck,

 

[tkatc]

Thanks Dave,

I don't think pressing the isolate button cleared up my tx but I would have to double check.

I can use a multimeter and will check continuity between my audio jacks and airframe. I assume you are talking about the headset audio jacks as opposed to the audio jack the radio uses to interface with the 340.

 

[Walt]

"Garbled" can also mean over-modulation. I don't own a Icom but I'm sure it has a mike level adjust in the main menu, maybe someone who owns one can tell you what that setting should be or you could just turn it down and see if it helps (helps to have someone with a handheld that can listen).

 

[David_Nelson]

Hi Tony,

I assume you are talking about the headset audio jacks as opposed to the audio jack the radio uses to interface with the 340.

You've got me on the audio jack the radio uses to interface with the 340. I'm not sure I understand that. For the whining problem, I was referring to the microphone, headphone, and music/entertainment jacks and making sure that a ground loop wasn't your problem.

I've observed the following with my 8000B:

With the unit removed:
- The outer portions of the microphone, headphone, and audio/entertainment jacks showed an open circuit (infinite resistance) to the air-frame.

With the unit installed:
- The outer portions of the mic and headphone jacks showed a closed circuit (zero resistance) to the air-frame.
- The outer portions of the audio/entertainment jacks showed an open circuit to the air-frame.

I looked at the installation schematics of a GMA-340 install manual and the above 'with unit removed' should test out the same.

The 100% sure method that the whining is not the result of a ground loop, is to remove the unit and perform the above checks. If we are to assume that the 8000 and 340 are somewhat similar internally (I certainly can't speak to that), maybe the "with unit installed" is good enough. If that doesn't test as expected, then remove the unit and see what you get.

Let us know what you discover -