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Old 03-07-2017, 02:06 PM
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AMillin AMillin is offline
 
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Default ADS-B Out and RF Coupling -- Static

Hello All,

My name is Andy. This post is regarding ADS-B Out and its affect on avionics. My interest is to share information that may be of interest to aircraft owners. Apologies for the length.

I built and fly a Velocity. Last fall I took the plunge and upgraded to become ADS-B Out compliant. I have a 430W and bought a freshly upgraded 330ES. The installation went well. After a software upgrade for the 430W, the system certified on the ground and, on the first flight had zero errors and qualified for my ADS-B rebate.

Upon installation of the 330ES, there was a moderately loud and persistent ticking in my headset. It was not there when I had the GTX-327 in the panel. To be clear, this isn’t a little ticking in the background. It is of moderate volume and constant. It is not affected by the volume controls.

ADS-B Out transmits a complex packet once a second, every second. Mode C & S transmit only when swept by the interrogation signal.

I asked Larry, the avionics tech at May Day Avionics, if he knew what it was. He did. He claimed it was RF coupling between the transponder signal and the other avionics. He had worked with other owners on the issue. He was never able to eliminate it. By moving the transponder antenna to a new location, further from the pilot, he was able to attenuate it; making it livable. Still, it was a fishing expedition.

I asked for help from the Velocity community. Several engineers stepped up and suggested tests to isolate the problem. After several rounds of testing, we had narrowed it specifically to the transmission from the transponder antenna interacting with the Bose A20 headset and the Garmin GMA-340 audio panel.

With the Bose A20 unplugged from the intercom, I turn the ANR on and I will hear the constant ticking. I can walk all the way around the aircraft and there is ticking. It can be perceived from as far away as 20 feet from the transponder antenna.

By plugging a David Clark H10-13.4 passive headset into the intercom, the ticking can be heard. If the Bose was plugged in and ANR left off, the static can be heard. The 340 was also picking up the static.

A bit of research on the internet and I found a few examples of this static from others. It is more prevalent in composite airframes. Aluminum airframes are less susceptible, but not immune.

Garmin: I spoke with the Garmin Experimental support team. Steve is on this forum. He was very helpful.

They suggested a larger ground plane on the antenna. The theory on the ground plane “may not fix the whole problem but it does change the radiation pattern of the RF that is not sent out the antenna.” There was no guidance other than “larger” and it could be a fishing expedition. I tried one 4X larger with no perceptible change.

They suggested I try the new GMA-245 audio panel. I wanted to know if they *knew* this would fix the problem. It will be an expensive test if it doesn’t work. Steve replied “The GMA 245 is a brand new 2016 digital design that incorporates some technology that might make it outperform the GMA 340 in this installation. When we were developing the GMA 245 we specifically tested it in my aircraft to make sure it could reject the transponder and COM radio RF signals in a composite aircraft.” He said he still can hear some static in his Long-EZ, but “It is pretty subtle and I tune it out in flight.”

Tim Hass at Approach Fast Stack sent me a 245 to test. It worked. The static being picked up by the 340 was not there in the 245. Thank you, Steve. Thank you, Garmin. Goodbye $550.

Bose: I started with their customer support department. Among other things, they suggested I move the transponder antenna further away – or – just remove the transponder from the airplane.

They had me send in my headsets for maintenance. They came back all shiny, but it didn’t change the static.

They replaced an A20 with the new, latest and greatest, Bluetooth enabled, just off the production line A20s. It didn’t’ change the static.

I pushed for a phone call with the customer support manager. It took a while but was finally put in contact with:

Miguel Menendez
Aviation Service Center Manager
Miguel_Menendez@bose.com
Direct: 508-766-1957
Fax: 508-766-5997


Miguel didn't know what ADS-B was, but he did know what a transponder was. He arranged a conference call with the team that designed and supports the A20.

I attended the meeting with the engineers from the Velocity community. The Bose team was very smart and very knowledgeable. They knew the problem intimately. They described it in great detail. They believe the coupling is happening in the ear cup; most likely the speaker and its wiring. No detail given.

The problem has to do with the power of the transmission and the proximity of electrical devices. It is not specific to any brand of transponder. It is not specific to Bose. It exists in Lightspeed headsets. Bose felt they were the best solution on the market. Kinda like being the “low tar” cigarette of ADS-B static.

At one point they had been contacted by Cirrus to help solve the problem. They did not go into detail what was done in that program. My take: It was easier or cheaper to help Cirrus than to fix the headset.

We offered to help find a solution. Bose rejected. They will not give access to proprietary information. There are many layers of protection and technology in the headsets. It is likely if we found a filter for the static we would be disturbing one of the other layers. They would not help us solve the problem.

Bose knew ADS-B was going to cause static in the headset back when it was designed 10 years ago. They said they had access to the equipment to test it then. They said the TSO specification was inadequate then and is inadequate now. The developed the headset to that specification.

Bose said there is no simple solution. They would need to re-engineer their product. They asked for 10 days so they could take this internally. We waited. They didn’t respond in 10 days. They didn’t respond in 21 days. I kept nagging. After a month, this was the response:
BOSE CONFIDENTIAL

Hi Andy,

Thank you for the additional testing and details you provided, they confirmed some of our suspicions. Based on your comment, “The static is present in the A20 (ANR OFF), and passive headsets when connected to the intercom.” it’s evident that the installation of the radio/intercom/wiring is also susceptible to the radiated energy from the new transponder/antennae. The fact that you have some susceptibility when wearing a passive headset when connected to the intercom, is an indicator of this.

In regards to the static present in the A20 (with the ANR on and disconnected from the aircraft), this also confirms what we talked about during our phone meeting. The field strength of the transmission in relation to the headset is high enough for the headset to ‘detect’ it. It is likely that the lower noise floor (residual background noise) with Noise Reduction ON makes the detected EMI more pronounced. We’ve found from other users with similar situations that improving the grounding and distance (meaning mount the antenna as far away as possible), have helped. We also know that many carbon fiber or fiber glass aircraft use embedded conductive fabric mesh or even metal grounding plates around the antennae and in the cockpit to help deflect some of the radiation.

As for the Bose A20, it is a TSO certified headset. It meets and in some areas even exceeds the FAA requirements for EMI. Setting up the Bose A20 to work in situations where the EMI levels are well above the TSO specification would involve a fundamental architectural change and not something we will do at this time. In addition –your specific situation may call for a modification beyond the headset to include a modification to your aircraft.

The feedback that we have from you is very helpful and is something that we will always take under consideration when developing new products. So thank you for reaching out to Bose on this work. Hopefully the information we provided you will help you continue your efforts to improve your flying experience.

Miguel Menendez
Service Center Manager
BOSE

Bose pretty much said, “Gosh, you paid a premium price for our headsets. Sucks to be you!”

The Bose people said the problem will be specific to each installation. Trying to find shielding at the 1090 frequency will not be trivial. If someone did find a solution, it may not transfer to the same type of airplane. Small differences matter. I’m not an engineer.

Despite the FAA’s urging, ADS-B out equipped aircraft are still a small fraction of the fleet. The problem is going to get bigger, not smaller.

If you have upgraded and you don’t have any perceptible static, then I am sincerely happy for you. FWIW, there are several Velocities ADS-B Out equipped and they have no perceptible static. I guess you won’t know you have a problem until you KNOW you have a problem.

If you have upgraded and you noticed the static, know you are not alone. If you have a Bose headset, you might want to drop Miguel a line and let him know. If you have another brand, I would love to hear what their support says. Most likely their first line of support will be unaware of it.

I have contacted AOPA and EAA. At this time they are both interested and want to advocate for us. It is their core mission. It might require the TSO be updated to take into account the new transponders.

If you wish to read more, here is a link to the very long thread on the Velocity Owners & Builders Association

For your information and education,
Andy Millin
Velocity N114MV
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amillin@sblglobal.net

Last edited by AMillin : 03-07-2017 at 02:11 PM.
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  #2  
Old 03-07-2017, 02:22 PM
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RV8JD RV8JD is offline
 
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Default Composite Airplane vs Metal Airplane Problem?

Is this a composite airplane problem, or does it affect metal airplanes too?
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  #3  
Old 03-07-2017, 03:14 PM
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jeffkersey jeffkersey is offline
 
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Default That might be my problem as well...

I recently upgraded to ADS-B out with a 330es. I also had a GMA 240 audio panel put in. I am getting static as well. Been too busy to try to trouble shoot but I bet it is the same thing you are talking about. I have light speed ZULU 2 headsets....
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  #4  
Old 03-07-2017, 03:23 PM
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AMillin AMillin is offline
 
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Default Wrong Place for this thread

My apologies. I did not mean to post this in the classified ads. I have re-posted in the General Forum.

Andy


[ed. I moved it ;^). Dr]
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  #5  
Old 03-07-2017, 03:45 PM
BobTurner BobTurner is offline
 
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Default

Quote:
Originally Posted by jeffkersey View Post
I recently upgraded to ADS-B out with a 330es. I also had a GMA 240 audio panel put in. I am getting static as well. Been too busy to try to trouble shoot but I bet it is the same thing you are talking about. I have light speed ZULU 2 headsets....
RV10, home made audio panel (all analog), Lightspeed Zulu 2, Trig TT-22 with the antenna directly under my butt...not a peep, no background noise. In a metal airplane, I'd be looking for poor grounds or poor grounding practice. In a fiberglass airplane...well, you're sitting on top of a (admitably pulsed) microwave oven. You really need thorough RF precautions.
I might wear an aluminum foil hat. -
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  #6  
Old 03-07-2017, 04:03 PM
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AMillin AMillin is offline
 
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Default Ground Loops Etc.

Bob,

A GREAT DEAL OF TESTING was done to eliminate poor grounds and ground loops. Ground loops also tend to take the form of a hum or whine that will change frequency with RPM. This is a steady clicking.

The avionics harness is an Approach Fast Stack. All aircraft grade, professionally made, shielded wiring.

The system was tested using a dummy load on the transponder. If the source was anything other than the transponder, the static would have been present while the dummy load was in place. It was not.

As I said, this is more likely in composite aircraft. Aluminium aircraft are less susceptible, but not immune.

I am happy you are not experiencing any problems.

Andy
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  #7  
Old 03-07-2017, 04:12 PM
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AMillin AMillin is offline
 
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Default Sample File

I made a recording of the static. I sandwiched my iPad between the ear cups of the A20. The A20 is not plugged into the intercom. The ANR is on.

Sample recording of the static.

Once you hear it, you can't un-hear it.
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  #8  
Old 03-07-2017, 04:19 PM
lr172 lr172 is offline
 
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Default

Quote:
Originally Posted by BobTurner View Post
RV10, home made audio panel (all analog), Lightspeed Zulu 2, Trig TT-22 with the antenna directly under my butt...not a peep, no background noise. In a metal airplane, I'd be looking for poor grounds or poor grounding practice. In a fiberglass airplane...well, you're sitting on top of a (admitably pulsed) microwave oven. You really need thorough RF precautions.
I might wear an aluminum foil hat. -
same setup and experience here, except no audio panel and RV-6.

Larry
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  #9  
Old 03-07-2017, 04:20 PM
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snopercod snopercod is offline
 
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Default excellent report

Thanks for the excellent report, Andy.
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  #10  
Old 03-07-2017, 04:56 PM
Canadian_JOY Canadian_JOY is offline
 
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Default

The nice thing with composite airplanes is that adding ground plane size can be done as simply as applying aluminum foil tape. While not ideal, this method is actually quite effective at improving protection of elements inside the airplane from high intensity radiated fields coming from such things as transponders.

On another note, I know this sounds corny, but try wrapping the Bose headset controller in aluminum foil.

With respect to the term "detecting" that was used in Andy's original post, often what the engineers mean is that the AC wave that is RF energy coming from the transponder is being picked up by the circuitry inside the headset, then a diode somewhere is "detecting" it as an amplitude modulated signal which in turn is amplified by the headset electronics. This is the same thing that happens when you can hear an AM radio station when you plug your guitar into your amplifier. The guitar pickup and its associated wiring make wonderful antennas for picking up AM radio signals!
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