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ADS-B Out and RF Coupling -- Static

AMillin

Member
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
[email protected]
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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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....
 
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]
 
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. -:)
 
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
 
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
 
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!
 
Shielding

I did try wrapping aluminum foil around the headset and the controller. I'm sure I looked ridiculous. There was some attenuation, not much, but some. The Bose engineers said there *might* be as well.

I also tried placing a sheet of .080 aluminum plate between the headset and the transponder antenna. Didn't do a thing.

Andy
 
System here:
Cozy MK IV, NavWorx 600EXP, GTX 327, GNS430, BoseX headsets
ADSB antenna under rear seats (~4' from headsets) with a 6" ground plane.
No problems/noise.
Suggestions:
1 Try installing snap-on ferrite cores on the headset cords, they sell them on Amazon of course! You may want to try 3-5 or more or as an experiment and/or use a larger ferrite core and wrap the cord through the core several times. Keep them close to the cups. If these are LEMO powered use ferrites on the power line also. These may not be practicle as a permanent fix, but it might help isolate the problem.
2 Borrow a bunch of headsets and see which is immune to the problem, try your headsets in other ADSB equipped aircraft.
Good luck
Tim Andres
 
Tim,

Thanks for the reply. As detailed in the original forum chain, ferrites were tried without success. They were tried in multiple locations including on the headset and its cable.

Multiple headsets were tried. 1) Bose and Lightspeed make up around 85% of the GA ANR headset market. 2) This is an issue with the TSO and is not specific to any manufacturer.

I have been working this issue for more than three months now. I have gotten some wonderful support from the aviation community.

I understand there is nothing more to troubleshoot in my airplane. I was told so by the manufacturers of the equipment. Until the TSO is changed and the product is re-engineered, I will have to tolerate the static, or I can remove the ADS-B Out transponder.

My hope with this post was to inform the community there is a problem. Some won't have any trouble, some will. If you don't hear static, then great! If you do, then you are probably in the same boat as me and many others.

Andy
 
ADS-B and headset noises

I have the FreeFlight ADS-B Ranger system installed in my RV-6A, GTX-327 now previous KT-76C, Lightspeed PFX headsets now and Zulu 2 previous, PMA6000MS intercom.

The ADS-B antenna was installed as far back in the fuselage as possible, and I only use the bottom. I don't have any noise issues with this or previous setups, but suspect that the distance and metal airframe help.

That said, I do have an interesting noise observation at my local Class D airport. KCYS, Cheyenne Regional, uses the Air National Guard for tower and traffic support. I noticed with my first ANR headset, Pilot Avionics, that I would get an occasional "chirp" in my headset. I finally figured out that if I was close enough to the Guard's rotating radar dish that it was causing it. It just so happened that when the dish would pass in my direction, that I would get a "chirp". I still get these in my newer Lightspeed headsets when within the same range, and have heard others say they had strange noises when around the Cheyenne Tower.

Sooooo, what can you do? Vans sells the sticky aluminum sheets for use in the fiberglass cowling to prevent heat damage. Could you use a large sheet of this around your antenna to block the radiation pattern toward your headset? Maybe add a second sheet between you and the antenna as a second block? Both sheets should be grounded to the antenna ground and the electrical ground. Did you ground the sheet of .080 that you used? Did you ground the shields that you put on the ear cups? Grounding the shielding makes it a shield and not just a sheet of metal hanging around. If you were close, I even have some leftover sticky sheet you could use to try.
 
Yes, it was tried with and without connection to the ship's ground. There was no change in the static.

Below is an email from Kevin Minckler. He is an engineer. He primarily works with digital signals. It helped me to better understand what we are dealing with:

---------------------------------------------

Hi Andy,

First I want to let you know that I am not an analog RF engineer, I'm more of a digital guy who's had some experience trying to snuff out EMI problems. It's interesting that you have to explain so much to the avionics group experts at Bose but not all that surprising. I'm not surprised they want to ignore the problem. Did you put big ferrites like you see on the cable to your video monitor on the mic boom? The reason I ask is those probably won't work for 1GHz. You probably need tiny ones that go on PC boards. What you want to do is look at the frequency attenuation plots of the ferrites you want to use and select ones that give the most attenuation at 1GHz. Companies that make ferrites are Wurth Electronics and Fair-rite. These places also have lab sample kits where you get a plastic tackle box full of all kinds of stuff to try. Engineers call these little bead ferrites "prayer beads" because we pray that they will work and fix the problem.

A 2D line-of-site type shield probably won't work. A 3D box shield around the headset might. The issues you are facing are what works may not be practical, manufacturable, implementable or look good. If I told you that if you had to wear a grounded metal waste basket over your head, well that would not be an acceptable solution.

I don't think increasing the ground plane of the antenna is going to help (but I have been wrong before). The reason I think this is that increasing the ground plane is probably only going to help the signal transmit better. You already have too much signal in the headset. On the other hand, if the whole bottom of the aircraft was ground plane as in a metal aircraft, that could help shield the signal from coming up into the cockpit. That might be the answer. The only way to find out is to try it with alum foil that is well grounded to aircraft.

I think you are beginning to see why this is a very difficult problem and so painful to fix. You have to try a lot of things. You may need some equipment like a real good scope (2GHz bandwidth min according to Nyquist theorem) and an RF sniffer loop. You need a box of shielding/gasketing material. You need a box of ferrites to play with. I would also suggest keeping notes on what you've done because 6 months down the road when you are still working on this SOB of a problem you are going to forget what helped and what didn't.

Maybe ask an avionics guy if he has run into this issue and what worked. The only one I know is Mike Esposito here:
https://flymechanic.com/stations/553/. His hangar is next to Whelen Engineering who sponsors Mike Goulian.
I bet he has some customers using Bose ANR headsets and ADSB in composite aircraft. He might have a suggestion.

I hope that helps some. I feel your pain. Keep trying!

Best regards,
Kevin
 
You might also buy or borrow a dummy load. Transmitting into that would at tell you if it is radiated rf causing the problem. If it does not go away when using the dummy, then you might start looking at noise on the DC buss.
You might also use a different piece of coax to feed the dummy, then you will also eliminate a poor connection on the coax. These can look great but have problems, and you are using something equal to RG 400 right?
Tim
 
Dummy Load

A Dummy Load was tried. It did confirm it is radiated RF. I am using RG 400. I did try another cable. Actually, I tried a certified transponder cable from a Cirrus.
No change in the static.
 
I'm curious about what type of antenna you are using, and if you experienced "clicks" with your previous transponder that corresponded with secondary radar interrogations?
 
I have a monopole with a 1/4 wave ground plane. It was tried with a much larger ground plane. The antenna is mounted between the main landing gear and protrudes from the bottom of the fuselage.

pic1076.jpg


pic1659.jpg


However, I also tested with a dipole.

11-04212a.jpg


It didn't make a noticeable change.
 
As another point of reference, I have a 23" x 23" grounded copper mesh the full width of the fuselage (yes, it is just 23" :)) in my Long-EZ to which the monopole transponder antenna and RG400 coax shield is connected.

The squitter sound in my Zulu ANR headset is fairly quiet, but noticeable. If I turn off the ANR, it goes away totally.

As Andy mentions, the GMA 245 and shielded aircraft headset wiring doesn't pick up the squitter and add it to the intercom. The Virb camera recordings I make in this aircraft are free of squitter noise whether I use a headset adapter cable, or a Bluetooth link from the GMA 245 to the camera.

When I fly with the same headset, GMA 245 audio panel, and GTX 45R transponder in our RV-7A, there is never any squitter noise in the headset.

Thanks,
Steve
 
Is this a composite airplane problem, or does it affect metal airplanes too?

Sounds like a composite airplane issue. I have Bose A20s (4 of them), a PS Engineering PMA 5000EX audio Panel and a Garmin GTX 23ES transponder (using a Delta Pop Blade antenna) configured for ADS-B out. I've never heard a peep on my A20's.
 
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It is not a composite issue. There are documented cases with aluminum air frames. Aluminum is less susceptible, but not immune. If you are not experiencing problems, I'm happy for you. There is one person, from this forum, with an RV, that reported the problem.
 
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This sounds strange, but have you tried a square ground plane? I read somewhere that circular ones might have an accidental resonance, changing the antenna characteristics.
 
The problem sounds an awful much like a ground issue. Have you checked all grounds to .25 milli ohms? You can't do this with a regular ohmmeter. There Is an adapter to make a cheap milliohmeter on Aeroelectric's website. If you have access to a commercial one great. Use it to check the grounding between all units and the airframe and the antenna to the ground plane. The grounds should be under 2.5 milli ohms (.0025 ohms) resistance. The major change with the ADS-B out transponder is that it is a higher power than the older GA transponders, and grounds, particularly antenna to ground plane ground problems will show up as reflected noise.
If this is a composite airplane, a ground plane to DC ground check is imperative also. You don't want the coax shield to be the principle ground for the ground plane, so antenna to ground plane checks must be done with the antenna connector removed.

Good luck.
 
For Sure ADS-B related...

Today I checked to make sure my noise was related to the 330es. System is quiet until the Transponder is turned on. Makes the clicking in ANR headphones and passive headphones...
 
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.

That said, it is the headset alone that is the problem. There are two ingredients to getting this kind of static: Sufficient field strength and a detection mechanism, an electric or electronic non-linearity that takes the envelope of the RF signal and brings it to base-band frequency where it can be audibly heard. (Yes, I am an electrical engineer with lots of analog, EMC, and RF experience) In your case, the detection mechanism is in the ANR electronics, and is indeed a design flaw. That said, given the ADS-B out frequency and field intensity, this kind of problem is hard to avoid.

Except for improvements from increasing the distance from the transponder antenna, there are no easy fixes, and it is certainly not a plastic airplane only problem. A metal plane is better off because the antenna has to be on the outside and the metal will attenuate the field inside somewhat. But, and this is why grounding is not that relevant, at the ADS-B frequency, the wavelength is so short, the signal gets in the windows and you can still have the static problem in a metal plane. As you saw, wrapping the headphones and controller helped, but didn't eliminate the problem, witness the ability of these short wavelength to get in so persistently, and also why grounding doesn't help - grounding mechanisms generally don't help much at these frequencies as they can be antennas as much as grounds. And the detection mechanism can be in many places and numerous forms, so the problem can occur with different headphones, or originate in the audio panel and its wiring.

I have a fiberglass Wheeler Express with Garmin GDL88 ADS-B out on a vertical dipole antenna inside, but way back in the tail, RG-400, and Bose A20s - no noise at all, so I guess I got lucky. But it does bring another thought - check the VSWR (voltage standing wave ratio) of your transponder antenna - if it is poor, then the reflected energy will increase the spurious filed strength. One thing to try is some good high frequency ferrites, say three of them an eight inch apart, slipped over the coax right at the antenna. Acts as a "ballun", or matching transformer, decreasing any reflected energy. And see if that helps.

Reinhard Metz
 
I noticed in reading the details on some manufacturers UAT transmitters that some create 40 watts of RF and some 20 in the experimental versions. Have you looked up the power out. The idea to do a good SWR measurement is accurate. Many of us are using transponder antennas and getting OK results, but the UAT is really at a lower frequency of 978. An antenna cut exactly for that is what is appropriate. My Bose picked up the missile radar over Salt Lake City winter Olympics. But I was locked by two F-16's. Another story for another day. The ANR is converting RF at a diode most likely... as mentioned. You certainly have been thorough in your testing. Thanks for sharing all the details.
 
For reference purposes, the VSWR?s of two typical antennas used for ADS-B / UAT.

The first plot is a stubby monopole transponder antenna.

2.623 @ 976.74 MHz
1.762 @ 1029.17 MHz
1.195 @ 1087.21 MHz

The second plot is a standard blade type transponder antenna.

1.364 @ 976.74 MHz
1.191 @ 1029.17 MHz
1.137 @ 1087.21 MHz


Data recorded with Anritsu lab grade equipment, calibrated with traceable standards.

8" dia ground plane.

2rp9o42.jpg


2zs9stw.jpg
 
Don, what kind of SWR plot do you get for a blade that is designed for a UAT? Rather than a transponder blade....
 
That said, it is the headset alone that is the problem. There are two ingredients to getting this kind of static: Sufficient field strength and a detection mechanism, an electric or electronic non-linearity that takes the envelope of the RF signal and brings it to base-band frequency where it can be audibly heard. (Yes, I am an electrical engineer with lots of analog, EMC, and RF experience) In your case, the detection mechanism is in the ANR electronics, and is indeed a design flaw. That said, given the ADS-B out frequency and field intensity, this kind of problem is hard to avoid.

Except for improvements from increasing the distance from the transponder antenna, there are no easy fixes, and it is certainly not a plastic airplane only problem. A metal plane is better off because the antenna has to be on the outside and the metal will attenuate the field inside somewhat. But, and this is why grounding is not that relevant, at the ADS-B frequency, the wavelength is so short, the signal gets in the windows and you can still have the static problem in a metal plane. As you saw, wrapping the headphones and controller helped, but didn't eliminate the problem, witness the ability of these short wavelength to get in so persistently, and also why grounding doesn't help - grounding mechanisms generally don't help much at these frequencies as they can be antennas as much as grounds. And the detection mechanism can be in many places and numerous forms, so the problem can occur with different headphones, or originate in the audio panel and its wiring.

I have a fiberglass Wheeler Express with Garmin GDL88 ADS-B out on a vertical dipole antenna inside, but way back in the tail, RG-400, and Bose A20s - no noise at all, so I guess I got lucky. But it does bring another thought - check the VSWR (voltage standing wave ratio) of your transponder antenna - if it is poor, then the reflected energy will increase the spurious filed strength. One thing to try is some good high frequency ferrites, say three of them an eight inch apart, slipped over the coax right at the antenna. Acts as a "ballun", or matching transformer, decreasing any reflected energy. And see if that helps.

Reinhard Metz

Reinhard,

Thanks for the reply. You are clearly are an engineer. The others I have gotten help from describe the problem just as you did. I am willing to try anything. I have tried so many things already. Can you give me the specifics on the high frequency ferrites you recommend? Possibly a link?

FWIW, the antenna on my plane is as far back as I can get it without putting it in the engine cowl.

Andy
 
I noticed in reading the details on some manufacturers UAT transmitters that some create 40 watts of RF and some 20 in the experimental versions. Have you looked up the power out. The idea to do a good SWR measurement is accurate. Many of us are using transponder antennas and getting OK results, but the UAT is really at a lower frequency of 978. An antenna cut exactly for that is what is appropriate. My Bose picked up the missile radar over Salt Lake City winter Olympics. But I was locked by two F-16's. Another story for another day. The ANR is converting RF at a diode most likely... as mentioned. You certainly have been thorough in your testing. Thanks for sharing all the details.

The 330ES is a 1090 solution, not a 978 UAT.
 
Cable?

Garmin says 8.8ft RG400 max and 1.5db max loss. You had a G327, now G330ES. RG304 for a 12.5ft cable, RG393 for 17ft length and 1.5db loss.
They do say "must not exceed"... could this yield an SWR that might
generate the "harmonics"....?? or just a loss of power?

I'm probably way off here.. John

And "Yes" I'm interested as I have a Glass ship and will use a 330ES...
 
I thought the same thing. I've been told by the engineers that the longer cable *might* effect the signal strength. I probably won't change the ADS-B static. To that end, I tried a very short, 4 ft., cable and it didn't change a thing.

All of the engineers have been cautious about talking in absolutes. RF problems seem to have a root in the dark arts. The only guarantee I can get is a problem like this can be very difficult to solve.

Andy
 
The fellow taking about the GDL-88 not having same issues is fine. Unfortunately the GDL-88 is a UAT out, not a 1090ES out and operates at a lower frequency than the GTX-330ES. This frequency shift alone could make all the difference.

I followed the FreeFlight advice of a 5.25" square ground plane to avoid resonance issues. They advise that a circular ground plane is one of the worst geometric shapes for ADS-B out. They also say as the square increases in size from the 5.25" square there is an attenuation loss until reaching a much larger size (something over 20"). Don't ask me the reason why .... I am but a dirt farmer and won't second-guess the engineers.

Here is a square ground plane I made for a fabric airplane:
Assembly.jpg


Remarkably, in the FreeFlight literature it shows both a max and a minimum length of coaxial cable depending on the type. For RG400 the minimum was very high like 15' and my antenna was only 5 feet away from the ADS-B box. So I went with the higher-loss RG316 double shielded coax since it's minimum was only 6 feet. So in the case of that manufacturer their equipment has to have some loss in the antenna system or interference happens. I found it incredulous to substitue my quality RG400 with the small diameter cheesy stuff like comes with handheld GPSs. But a quick email to FreeFlight confirmed their minimum coax lengths based on loss. I could have even used that black single-shielded RG174 to satisfy the loss requirement designed into the system.

And all this time I thought I was being a good boy by limiting the antenna lead lengths and using only the highest quality coax. That rule of thumb went out the window in the case of my ADS-B installs.

So you might re-try a square ground plane with some lower quality coax. Or at a minimum run the question by Garmin of the need for attenuation in the antenna connections and lead run length minimums.

Jim
 
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Or at a minimum run the question by Garmin of the need for attenuation in the antenna connections and lead run length minimums.

Jim

Steve, from Garmin, has been monitoring this thread. Perhaps he will chime in...

Andy
 
. RF problems seem to have a root in the dark arts.
Andy

That's true. Look inside some RF boxes and you can see something that looks like voodoo beads. I personally have seen a slightly corroded ground connection act as a diode, and generate harmonics all over the place.

Maybe I missed it. Are you able to borrow a signal generator and SWR meter? That might tell you something useful, or not.
 
Steve, from Garmin, has been monitoring this thread. Perhaps he will chime in...

Andy

Hello Andy,

No, the GTX 330ES installation manual doesn't specify a minimum attenuation, just the 1.5 dB max (including connectors).

My installation uses about 4 ft of RG-400 cable, and the one in our RV-7A is probably only about 3 ft since the transponder is mounted in the tail next to the antenna.

Both aircraft get excellent "scores" on the FAA ADS-B Out performance reports.

Thanks,
Steve
 
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Bob,

I might have a friend with an SWR meter. Maybe worth a check. I have tried it with three different antennas without a change in ADS-B static.

Andy
 
Bob,

I might have a friend with an SWR meter. Maybe worth a check. I have tried it with three different antennas without a change in ADS-B static.

Andy

Yes, I think it's a long shot, too.

Here's another long shot, but easy to test: totally disconnect the ELT antenna. I've heard of cases of a signal propagating down into an ELT, being rectified and generating harmonics, then being re-radiated.
 
I got my hands on an SWR meter. I've never used one before. I took it out to the hangar and got out the instructions. Ha. To do the test I need something that will transmit continuously at 1090. I don't have a source like that. Doesn't look like I will be able to perform this test.
 
Hi Andy,
Please clarify if you would....

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.


A Dummy Load was tried. It did confirm it is radiated RF.


Does the 245 correct the problem in both the passive and active headset modes? Was this accomplished with just a slip in and out install?


For Steve @ Garmin... Have you tried the new and improved 245 model back shell to eliminate noise issues on previous versions? (IE Jeffs-GMA 240...and any 340 models) Jeff's post
 
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Same Problem here

I have a Trig TT-22 1090ES transponder connected to a Comant CI-305 antenna with RG-400 cable in a Lancair Legacy and am having the same ticking issue. The cable is about 5 feet to the antenna mounting location on the center of the belly of the aircraft about mid wing cord.

As the fuselage is carbon, there is no ground plane installed. The unit is grounded through the shield and the carbon fuselage.

The same transponder in is installed my RV-8. Swapping them is no help. The ticking is just barely perceptible in the RV and is not an issue, but super annoying in the Lancair.

The noise happens with both active and passive noise canceling headsets.

One interesting thing is that placing my feet on the Lancair rudder pedals while in flight gets rid of 80% of the noise. RF magic, I guess.

Will be following this thread closely in hopes of a solution.
 
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One interesting thing is that placing my feet on the Lancair rudder pedals while in flight gets rid of 80% of the noise. RF magic, I guess.

Hi Chuck...Just a couple things. Are you using a GMA 240 or 340 also?

And instead of touching the pedals...would the noise decease if you where to say, touch a known aircraft ground?
 
Additional Info

The Lancair has an Apollo SL 15 audio panel and the RV has an AP ? 60 audio mixer without an audio panel. An Apollo SL70 transponder was previously installed in the Lancair using the same antenna and cabling and had no noise issues

The Lancair transponder antenna base is installed in a recessed pad on the belly of the aircraft.

Touching the Lancair rudder pedals on the ground does not change the noise. This only reduces the noise in flight. I will bring out a ground wire to be touched during flight and see if it has the same effect on my next flight.
 
T.C.,

It improved the situation for anything plugged into it. I was getting static coupling in the Garmin 340 and independently in the Bose A20. When using both, the static was doubled as it was coming from the headset and the audio panel.

The 245 seems to have some sort of software solution in it. When talking or receiving the intercom is "active" and the static is there in the background. It is diminished, but still there. When "passive" it is filtered out and quiet. Much better. Not perfect, but liveable.

Since Bose has said we are screwed if we have a problem, my only issue is still with the Bose A20.

Andy
 
Not perfect, but liveable.

Since Bose has said we are screwed if we have a problem, my only issue is still with the Bose A20.

Andy

Hi Andy,

Good to hear from you. Sorry to see you haven't found the "magic pill" but glad you have an acceptable work around...

I did not sign up on the other forum to see all the many fixes tried. But I keep coming back to the transponders output being the source of the problem with RFI being the path... Now, how to block or deflect it's effects...

Did you ever get a good VSWR check? Is the noise LOUDER on the ground?

How did the other good (no noise) Velocity antenna installations differ from yours?

Your probably sick to death of this problem, but if you want to hear some ground plane and antenna suggestions, let me know.

Oh, and you asked about ferrites... Look here...

Lastly:p with your new 245 install did you upgrade to the newer style backshell with improved grounding?

Best regards,
 
Just curious...How do you guys with carbon airplanes make a good connection to the carbon with the antenna base and/or coax braid?
 
If I am not mistaken... you are asking about bonding to composites. You don't. You can imbed conductive material, or you can create a ground plane with metal. Then, a strap or other conductive path leads from the base of the antenna to the conductive material. If it does not conduct, it will not act as a counterpoise to any antenna. Did that just muddy the waters?
 
Hi Andy,
Please clarify if you would....

Does the 245 correct the problem in both the passive and active headset modes? Was this accomplished with just a slip in and out install?

For Steve @ Garmin... Have you tried the new and improved 245 model back shell to eliminate noise issues on previous versions? (IE Jeffs-GMA 240...and any 340 models) Jeff's post

Hello T.C.,

My experience is that the GMA 245 does correct the issue of the audio panel being affected by the 1090ES extended squitter in fiberglass aircraft. It does not, however, stop an ANR headset from picking up noise if it is prone to do that.

In other words, with the GMA 245 installed, if you turn the ANR off and use the ANR headset without it, you don't hear the transponder squitter.

When I installed the GMA 245 into the GMA 240/340 rack, I did not change out the connector backshells to the new style as that was not necessary to eliminate the issue. With proper cable shielding and termination, the new metal backshells do not significantly change the installation.

Someone suggested that software in the GMA 245 addressed this issue. That is not the case. The hardware design was changed to reject this signal.

Thanks,
Steve
 
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