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ADS-B question

ksauce

Well Known Member
Patron
All,

While building, I'm flying a Grumman Tiger (it's almost a certified RV-9A) in a club. It seems that our club's not-so-old Bendix King KT73 mode S transponder is dying. It's an orphan with a flat rate repair fee of $3000. Considering we can buy a new ADS-B transponder with a WAAS source for not much more than that right now and that we would eventually have to cross that bridge, we're thinking it's time to pull the trigger on a 2020 compliant system.

So...which integrated transponder do we choose? The easy option is Garmin's GTX 335 with internal WAAS. Presently, we don't need ADS-B in as three of us pooled our money and bought a Stratus 2s. We love it, it's great. Reading up on ADS-B in and out on an FAA site I'm concerned about us getting "degraded" ADS-B in service even though we would be compliant. There's a thread somewhere on VAF about this, too.

With the Garmin, I THINK the system would see us as two clients. One would be our Stratus for ADS-B in that would show SIL=0 and the other would be the GTX335. In this instance, I don't think the system would give us all the benefits that are meant to come with ADS-B.

Another option is Appaero's transponder, but that makes me nervous as I don't know how long Appaero will be around and it seems silly to buy a panel mount device because we have a portable (and likely consumer grade) piece of electronics.

The third option is buy the GTX 345 and sell the Stratus. It apparently works with Foreflight.

Does anyone have any insight into the ins and out of IN/OUT?
 
Please define "degraded" ADS-B. Never heard that terminology?
The only time I have heard that term is if you only have Ads-b IN.
You would then rely on aircraft around you to "ping" the ground station.
 
I also have the Garmin GTX 345 (thanks for all your guidance on the install Alton!).

It works really well with my Ipad using Foreflight. Automatically connects via blue tooth.

I also have a 660 connected to the 345. Awesome!
 
Please define "degraded" ADS-B. Never heard that terminology?
The only time I have heard that term is if you only have Ads-b IN.
You would then rely on aircraft around you to "ping" the ground station.

The ground based transmitters will only send the full complement of traffic information if your transponder tells it what it can receive. The stratus like units will only receive what is broadcast (which is Mode C only, I think). A user on reddit replied to my question with the following:

"You have some misinformation. Your stratus does not transmit anything (to the Ground Based Transmitters; GBTs) so the FAA does not see that device as a client. The stratus is receive only, and the 2s is a dual frequency receiver meaning it listens on both 978 (weather and some traffic), and 1090 (traffic only). The GTX345 is a transmitter on 1090 and a receiver on both frequencies. Most importantly is what the GBT sees is your RECEIVE capability. With each OUT message, you tell the GBT what your RECEIVE capability is. If you indicate that your airplane can RECEIVE on both frequencies, the GBT will only send you MODE-C traffic and assumes you can receive the 1090 and 978 broadcasts directly. If you indicate you can receive only 978, the GBT will send you all 1090 traffic (called TIS-R) and MODE-C traffic but not the 978 traffic you receive directly.
Why this is important is that the GBT which you are "connected" to may not be visible from your stratus. The stratus has REALLY bad reception, so if the particular GBT which the FAA thinks you're closest to isn't visible by the stratus due to airplane structure, you will not see any MODE-C traffic even though its being sent to you."

It's starting to be a bit more clear to me. We won't see anything but the mode-c targets on the stratus. We would need the GTX345 to receive the 1090 and 978 traffic details directly.

Man this is a can of worms.
 
That's not at all what he said. He said that in his opinion the Stratux is a poor receiver, so you will miss transmissions, both air to air and ground to air. What is your experience? A lot depends on the antenna used. If you consistently see lots of ground stations, then your plan should work okay.
edit: The only info the FAA ground stations know about your ADSB-in box is what frequency (s), if any, you are listening on (that info is sent by your ADSB-out system). There are no specifications (SIL level, etc) for the -in box, because they aren't required. (for certified aircraft installed equipment needs to be shown that they do no harm). Question: Do you already have a Garmin 400w/500w/GTN series box on-board? If so that can be used for the gps, saving you some money.
 
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The ground based transmitters will only send the full complement of traffic information if your transponder tells it what it can receive. The stratus like units will only receive what is broadcast (which is Mode C only, I think). A user on reddit replied to my question with the following:

"You have some misinformation. Your stratus does not transmit anything (to the Ground Based Transmitters; GBTs) so the FAA does not see that device as a client. The stratus is receive only, and the 2s is a dual frequency receiver meaning it listens on both 978 (weather and some traffic), and 1090 (traffic only). The GTX345 is a transmitter on 1090 and a receiver on both frequencies. Most importantly is what the GBT sees is your RECEIVE capability. With each OUT message, you tell the GBT what your RECEIVE capability is. If you indicate that your airplane can RECEIVE on both frequencies, the GBT will only send you MODE-C traffic and assumes you can receive the 1090 and 978 broadcasts directly. If you indicate you can receive only 978, the GBT will send you all 1090 traffic (called TIS-R) and MODE-C traffic but not the 978 traffic you receive directly.
Why this is important is that the GBT which you are "connected" to may not be visible from your stratus. The stratus has REALLY bad reception, so if the particular GBT which the FAA thinks you're closest to isn't visible by the stratus due to airplane structure, you will not see any MODE-C traffic even though its being sent to you."

It's starting to be a bit more clear to me. We won't see anything but the mode-c targets on the stratus. We would need the GTX345 to receive the 1090 and 978 traffic details directly.

Man this is a can of worms.

Please do not confuse the Stratus ADS-B In receiver with the Appareo Stratus ESG Mode-S Transponder that is ADS-B out compliant.

There are 3 different Appereo Stratus devices. Stratus (1, 2, 2S) for ADS-B in and two (2) different Stratus ESG Mode S transponders that are ADS-B out compliant and includes built in GPS source.

AOPA did a nice write up on the Stratus ESG.

The Stratus ESG is my baseline 2020 unit. It is ready for International travel (Canada & Bahamas) and can go above 18,000 MSL. Good company and great simple solution. I believe that Appareo has a winner with their Stratus ESG.
 
That's not at all what he said. He said that in his opinion the Stratux is a poor receiver, so you will miss transmissions, both air to air and ground to air. What is your experience? A lot depends on the antenna used. If you consistently see lots of ground stations, then your plan should work okay.
edit: The only info the FAA ground stations know about your ADSB-in box is what frequency (s), if any, you are listening on (that info is sent by your ADSB-out system). There are no specifications (SIL level, etc) for the -in box, because they aren't required. (for certified aircraft installed equipment needs to be shown that they do no harm). Question: Do you already have a Garmin 400w/500w/GTN series box on-board? If so that can be used for the gps, saving you some money.

So now I'm more confused. Does the Stratus (note: not stratux) talk to any ground stations? I thought it was just receiving whatever was broadcast by the ground stations and that the FAA wouldn't be broadcasting all traffic as it would overwhelm the spectrum. Based on the reddit guy's reply, I think I need an ADS-B out device to announce, hey, we can receive x, y, and z. The ground station would send some sort of traffic (which I wouldn't get without the 345 or equivalent) and I'd pick up the other traffic that is broadcasting itself to the world.

We're currently rocking a KLN94. So we either buy the internal waas or I really try to convince the owner to pony up for at least a GTN625. But we've got that faulty display in the NavComm so maybe we just do the 650.

Oy vey this is complicated and I'm a technical guy. I'd love to see a matrix that explains all this.
 
Please do not confuse the Stratus ADS-B In receiver with the Appareo Stratus ESG Mode-S Transponder that is ADS-B out compliant.

There are 3 different Appereo Stratus devices. Stratus (1, 2, 2S) for ADS-B in and two (2) different Stratus ESG Mode S transponders that are ADS-B out compliant and includes built in GPS source.

AOPA did a nice write up on the Stratus ESG.

The Stratus ESG is my baseline 2020 unit. It is ready for International travel (Canada & Bahamas) and can go above 18,000 MSL. Good company and great simple solution. I believe that Appareo has a winner with their Stratus ESG.

Yep, understood. We have the 2S. I've been looking at the ESG. I'm nervous about buying this as I worry about the long term support of the device. Will Appareo be around in 10 years? Will we get support? It also doesn't have ADS-B in so when the stratus does die we'll have to buy another one. Will THAT be available? Again, my suspicions are based on the fact that the Stratus is a piece of consumer electronics (albeit expensive) and the goal is always sell a new shiny device. We will likely eventually want to feed WAAS approach unit and I don't think the ESG will.

Granted, some of my concerns are also valid with garmin but they seem to have a good track record. Heck, they're still supporting the 430/530 (yes, I know they've dropped some other stuff like the Apollo AT stuff).

This isn't meant to be a swipe at your 2020 choice at all. I'm just concerned about long term planning.
 
So now I'm more confused. Does the Stratus (note: not stratux) talk to any ground stations? I thought it was just receiving whatever was broadcast by the ground stations and that the FAA wouldn't be broadcasting all traffic as it would overwhelm the spectrum. Based on the reddit guy's reply, I think I need an ADS-B out device to announce, hey, we can receive x, y, and z. The ground station would send some sort of traffic (which I wouldn't get without the 345 or equivalent) and I'd pick up the other traffic that is broadcasting itself to the world.

We're currently rocking a KLN94. So we either buy the internal waas or I really try to convince the owner to pony up for at least a GTN625. But we've got that faulty display in the NavComm so maybe we just do the 650.
his.

Yes, the Stratus is just a receiver. Your reddit friend's concern is whether or not it actually works well enough to reliably pick up ground stations. If you use an internal antenna inside a metal airplane, he may be right. But it is easy enough to fly around and see how well you do. Doesn't it display the number of ground stations it's receiving?
Yes, you need an ADSB-out box to trigger the ground station to send you traffic ( weather is sent without any 'trigger').All ADSB-out boxes tell the ground station what frequency you are listening on.
Yes, you should get other ADSB-out equipped aircraft directly, without need of the ground station. You should be seeing them now. So the ground station is mostly useful for mode-C aircraft (detected by ATC radar). (ground stations also send up the weather).
Check on your King gps upgrade. Just because it is WAAS does not mean it is approved as an ADSB position source. The ADSB specifications are very tight. Garmin 400W/500W/GTN series boxes are approved but only with the latest software version. And your ADSB out device must be able to 'read' Garmin's "ADSB+" format. (In its wisdom the FAA did not specify data formats, so there are a bunch of propriatary ones out there). Obvious Garmin transponders will read this; so will Trig transponders.
And then there's the question of how you will display all this data.
One thing you've figured out correctly; it is complicated!
 
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It also doesn't have ADS-B in so when the stratus does die we'll have to buy another one. Will THAT be available? Again, my suspicions are based on the fact that the Stratus is a piece of consumer electronics (albeit expensive) and the goal is always sell a new shiny device. We will likely eventually want to feed WAAS approach unit and I don't think the ESG will

There is a Stratus ESGi that does include ADS-B in. Essentially, they add a Stratus 2S to the base unit, but without the internal battery or antennas.

You cannot use the internal GPS signals from any of these ADS-B units (Appareao, Garmin, Lunx, etc.) to shoot IFR approaches. At best, you can use the internal GPS to drive a tablet that doesn't have its own GPS. I doubt you'll ever have an IFR approach unit that doesn't use its own GPS.

I'm looking at what I want to put in in my certified plane, and share your uncertainty about long term availability of the Appareo units. However, Garmin was new too at one point. There is a significant cost difference, and for Many planes, an ADS-B installation can cost 20-25% of the plane's market value that can't be recovered.
 
GPS Antenna Location

If a GPS antenna is located too close to a transmitting antenna, the GPS signal might be lost while the transmitter is transmitting. Loss of GPS signal for a few seconds might not matter to the pilot for navigating purposes. However it will matter to the FAA if the GPS is being used as a position source for a 2020 compliant ADS-B-OUT system.

Below was posted on a Dynon FORUM by By Paul Kuntz
FAA ADS-B Compliance Report . . .came back reporting non-compliance for the NIC (Navigation Integrity Category) parameter. . . .
After downloading compliance reports for other flights and thinking about it a bit, I have concluded that the very likely problem is that my GPS is being swamped whenever I transmit on my VHF radio. The length of the outages in the FAA compliance reports are consistent with that being the case, and I violated Dynon guidance for antenna placement when I installed the SV-GPS-2020 receiver puck. My original Dynon GPS receiver was only about 14 inches from the VHF antenna, but it worked fine, so I elected to simply swap it for the new GPS. That location is suitable for good Skyview Nav performance, but there are apparently GPS outages during VHF transmission that I don't notice, but are noticeable to the FAA system.
To test this theory, I flew a couple of days ago, and did not use the radio at all during the flight except to announce my takeoff and pattern entry. The compliance report for that flight came back with no exceptions.
So my next move will be to bite the bullet and move the GPS antenna further away from the VHF antenna.
 
ADS-B

As I'm sure you know, there are many options. Most economically replace your transponder with any current transponder (MANY good deals right now) and buy the Navworx that uses the old transponder. Options are available for Ipad (wifi), transmit capability to big screens and for a GPS antenna, the Garmin GA56 is approved and are plentiful since removed from WAAS installations.
 
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