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Touring Motor Gliders Association (TMGA)

com radio static


Gfeldman

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Hi Phoenix owners,

Today while flying my plane I was experienced    loud static on my com radio that didn't go away when I changed frequencies. Eric I know a few years back you encountered this. 

How did you trouble shoot and did you ever find a cause? I will remove the seat to trace the PTT wires integrity. I think you said that Jim separated some wires in the panel. Can you give me a few more details. 

I have in the past heard interference when I had my strobes on that abated when I turned them off. I also used my handheld transceiver and could detect no static so I think it originates inside the plane.

George 

N33GF

 

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Hi George,

Sorry to hear about your difficulty.You may have already thought of some of this, but I thought I’d suggest it anyway. I am a ham radio operator, and I’m frequently tracing down new instances of interference in my radios, and I usually have to do a systematic step-by-step process to figure it out. One thing that you might want to do first before you pull the seats and start looking at wiring is doing a formal history of the event and then a systematic process of elimination system by system to get a better handle on the source of the static.

1. Is there a clue in when it started and how it started? Did it suddenly appear or did it build? What were you doing at the time when you first noticed it? Where were you when you first noticed it? Did you make any configuration changes in the aircraft right before it started? Does anything correlate with the initiation or modification of the static?

2. Think about the nature of the static.  Is there something about the type of static that would give you a clue? Is it a constant hash like white noise, is it pulsing, does it have any rythmicity to it? Was it affected by heading or power settings? Did anything modify it such as your position in the seat? Did it appear in both speaker in the headphones? Did it ever go away or change in any manner? Is it uniform across all frequencies? Did you bring anything with you on that flight that was different? For example, plug-in USB chargers and power supplies can create a tremendous amount of radio frequency interference. Did anything in your configuration change? Try to remember everything you can about the moment appeared.

3. If you don’t get any clues from the above history,  I suggest that you make a list of all the switches and modes (e.g., autopilot configurations) in which the plane can operate and run through the list first with the engine off and then with it on and then at different rpm settings. If the static comes on, keep going through the list and see if it changes with additional switches. The appearance or absence or modification of the static should narrow down your search of where to focus.

I realize that you’ve probably thought of or done most of what I’ve listed here, So I’m just giving you an example of how to start over to elicit some clues that you need so that you don’t end up chasing random wires. My experience in chasing down interference in my radios has always failed whenever I try to take shortcuts. I’ve been able to find nearly every instance of interference by starting with turning off the power in the house and adding circuits one by one until the interference appears. That always narrows down the search significantly. The one advantage you have in the airplane is that because you’re moving over a wide range of locations you can eliminate external sources right away. Sometimes I’ve had to go to a neighbor and find out if they’re doing anything different.

If this process of elimination doesn’t yield any results, there may be a new fault, possibly a loose or corroded ground, and that could be either in the engine compartment or anywhere else in the aircraft. One of the best tricks I have for localizing source is taking a small battery powered radio set to an empty AM frequency and moving it around the cockpit and engine area to find the max volume of the static.

Good luck tracking this down. There’s really a lot of additional things you can do, and I’m only suggesting some hints to get you started. The most important thing is that you turn into a detective.  It’s really a Sherlock Holmes event, and as a good detective says, after you’ve eliminated all the logical possibilities that which is the left has to be the cause no matter how improbable.

if you get stuck we can chat by phone and figure out next steps.

Ed


 

 

 

 

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Hi all,

So the com radio static issue is solved thanks to Ed's suggestion to think broadly about the problem. On the morning when the problem first occurred I had placed the right angle vent that Jim Lee made in the passenger side sliding vent of the cockpit. It has been unbearably hot and I thought that extra airflow would help. Dave Glosser has been using this on his Phoenix without incident. Today I flew the Phoenix without the additional vent without changing anything else and all radio static disappeared.

I use a noise cancelling One-X David Clark headset and I think there are some air flow conditions that make this particular headset go crazy.

What I've learned from this incident is that its a good idea to have a backup handheld transceiver on hand, ideally hooked up to an outside antenna just in case.

Thinking back I could have done something really simple in the air when this problem occurred by simply turning off the noise cancelling feature of the headset but

my brain was way overloaded at that point.

Ed thanks so much for saving me hours of what would have been fruitless trouble shooting.

George

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I'm glad you solved your problem, as I never found what was causing my static years ago. It went away after fiddling with some connectors and hasn't come back.  Currently I am chasing a whine in my motorhome satellite radio that comes and goes, so I'll reread Ed's advice and see if that will help solve it.

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Hi George, glad you found it.  I'm taller than you, and the "air conditioner" blows low enough so that it doesn't generally hit my mic. I only need the a/c when on the ground and generally stuff a microfiber cloth into the thing once I get to altitude where it's cooler. Another simple measure I've taken is to crank up the squelch as needed to defeat the noise on the ground. It's been miserably hot the last few weeks. 

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