Transponders & ADSB - Help Me Obi Wan Kenobi

Sinistar

Sinistar

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Brad
First things first, our plane is not ADSB out equipped yet. We also do not have any RNAV based equipment (just VOR's and DME). We are currently using a Garmin GDL-39 for incoming wx and traffic.
  1. The GDL39 has a screw in antennae on top. Curious if I have this right...this antennae must receive at least (2) things????
    1. The ADSB ground based transmissions (ADSB wx and ADSB traffic within a puck) but only when GBT's are being received.
    2. It also seems to receive direct transponder data from certain transponders (mode 'S' ??) as I can see the major airline flights and a few GA traffic even when sitting at home (where I have verified the GBT is not received).
    3. So where is the ideal position for this antennae??? It would seem you want it up higher to receive the direct Mode 'S' transmissions but it really seems best mounted down low to receive the ADSB GBT's??? Do some of the dedicated ADSB-in devices use separate antennae's for this?
  2. The GDL39 seems to have a internal GPS antennae with an optional external antennae connection.
    1. Obviously the ideal GPS antennae location is on top of the plane somewhere - right???
And now a transponder question or two or whatever :)

Not counting the newest ADSB based transponders, how many pre-ADSB transponders are out there that send out Mode 'S' information?? I ask this because I like that I see traffic even though its not ADSB. And it would seem in the ideal world, updating to this type of transponder would provide the most positional data to others (at the expense of privacy - but that doesn't bother me).

So now a ADSB out equipping question: If I wanted to just stick with our GDL39 for ADSB in and equip with the GDL82 for ADSB out, could I also swap in a used transponder that is Mode 'S' capable and come out cheaper than the Garmin 345 solution. Maybe put another way, are used Mode 'S' transponders being pulled in favor of the Garmin 345 solution and possibly provide a cheaper overall solution.

Or maybe I don't understand Mode 'S' properly - does it need a WAAS GPS source and hence there is no such thing as a cheap used transponder? Does it have to be swept by a radar for me to see it or is it always sending something?

Last question: Can a receiving antennae be shared? For example, if two different components require a external GPS antennae - can that antennae be shared and still provide enough signal strength to each receiving device?
 
Many consider the best ADS-B transponder either the Lynx-9000 or Garmin GTX-345, and for good reason. They are well worth the extra scratch. Garmin's sale price on the GTX-335 with WAAS position source and WAAS antenna is $2995 list price. Dealers cheaper. Installation is not complicated for the 335 and cheaper than the 345.

All three of theses units put out 240 watts of power.

It's personal preference, but would rather not have an appliance that's between the transponder and the antenna and only putting out the minimum 18-22 watts.

A lot of folks have very old transponders, and should considering replacing, and ADS-B is a great reason. Just my opinions.

The going rate for S mode GTX-330's is about $1500, and with Extended Squitter (ADS-B out) are about $3000. Garmin will upgrade an existing 330 from S to ES for about $1500. The 330 needs an external WAAS position source.

I'd rather get a new GTX-335 for that price.
 
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Also new equipment qualifies for the FAA $500 rebate. Making the GTX-335 only $2495 until Dec 31st. At that price not sure I'd fiddle with a 330.
 
Who really cares about old TIS after they get real ADS-B in?
 
Here are some sources to read:

https://airfactsjournal.com/2013/01/ads-b-101-what-it-is-and-why-you-should-care/
https://www.aopa.org/go-fly/aircraft-and-ownership/ads-b

Briefly, you will typically have one of two ADS-B OUT frequencies (978 or 1090) and may have 1090 (ES), 978 (UAT), or dual link (both ES and UAT) IN. Any ADS-B installation requires a WAAS GPS source, either from an approved panel unit (e.g. GNS, GTN series) or a dedicated unit that accompanies or is built in to the ADS-B device. If you have multiple GPS devices it is sometimes possible to share a GPS antenna, but is usually not recommended.

FYI, the GPS antenna is only for GPS reception, and is typically on the top of the aircraft. It is usually a hockey puck shaped unit. The 1090 and/or 978 MHz signals pass through your L-band (transponder) antenna, which is typically on the bottom of your aircraft, but you can also install additional antennae for better reception ("diversity" option). (This is for permanently installed units, not portable ones.)

What do the various frequencies do? You broadcast your position on your OUT frequency (UAT or ES, typically). You can receive traffic information on your IN frequencies (UAT, ES, or dual). If you are UAT IN only, you can see UAT equipped aircraft directly, 1090 ES equipped aircraft indirectly through ground rebroadcast on UAT, (ADS-R) and non-equipped Mode A/C aircraft via TIS-B ground rebroadcast of their radar position. If you are 1090 ES IN only, you can see 1090 ES traffic directly, UAT traffic via ground rebroadcast via 1090 ES, and Mode A/C only aircraft via TIS-B ground rebroadcast of radar position. If you are dual link, you can see both UAT and 1090 ES aircraft directly, and Mode A/C aircraft via TIS-B ground rebroadcast of radar position. Weather products (FIS-B) come only through UAT. I think this is all correct. Confusing, but it basically works really well.

So, as an example, I have a GNS-430W and decided to install an NGT-9000 1090ES OUT and dual-link IN unit. The NGT-9000 has its own WAAS unit built in, so I hooked that up to a second GPS antenna topside. The NGT-9000 pulls altitude info from my blind encoder, and broadcasts my position on 1090 ES. I receive traffic information directly from both UAT and 1090 ES frequencies, and TIS-B for Mode A/C aircraft. I also get weather (FIS-B) via UAT. In my case, a shared GPS antenna was NOT recommended. I am still using my previous L-band (Transponder) antenna on the bottom of the airplane. I did not opt for the "diversity" option.

A GDL-82 uses your existing transponder to obtain squawk code and pressure altitude, and broadcasts that information along with your GPS position on the UAT frequency. I don't think the GDL-82 cares what transponder you have as long as it is Mode C compatible and is working properly. All ADS-B solutions require an approved WAAS GPS data source to function. The GDL-82 itself is an approved source.

Cheers, and good luck. It's a bit of a morass to figure out how you would like to comply.
 
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bnt83 said:
Who really cares about old TIS after they get real ADS-B in?
Click to expand...

I think the TIS-B feed is still helpful for locating Mode A/C only equipped aircraft. Flying back to my home field a few days ago, my NGT-9000 spotted several departing aircraft squawking Mode C only as I arrived in the pattern. The big iron that was coming in was transmitting 1090ES positions.
 
Choices are yours, but if you're going to have ONLY one WAAS position source, put it in a navigator where you can get some good use of it, and feed it to some silly out box like a 330ES.

spending the (yes) extra money for a 345 won't buy you any approach guidance, and a GDL-39 puts plenty of stuff to de-clutter on your tablet or dedicated aviation handheld (696 in my case)
 
My 2¢... Decide on whether or not you're ever going to upgrade to /G. If you are it's pretty clear you will want to go the GTX 335 or GTX 345 route. If you're not then you may want to consider a Stratus ES or Stratus ESGi. I decided last year that I wasn't going to be flying IFR in my aircraft so no need for a /G upgrade in the future. The Stratus ESGi provides great VFR situational awareness at a decent discount when comparing against the Garmin offerings. If I ever do decide to go /G it would mean replacing the GPS antenna, only slightly complicating the installation - but I wouldn't have the traffic on the navigator and still need ipad.
 
I upgraded to ADS-B out in 2015 with a KT-74 squawking my GPS position from my 430W. The transponder and install were around $4500 total. I use a GDL39-3D for my ADS-B In. There are much less expensive options now. If you have a UAT, such as the GDL 82, you don't need mode S at all. Uavionix has a good deal on their products as well and both can take the squawk code from your Mode C transponder and both are under $2k and can be installed by your A&P. Despite the cost, the ADS-B out advantage is a giant leap in safety. Once you have ADS-B out, and any ADS-B In solution, Stratus, GDL, etc. you'll be able to see all the traffic that ATC can see (TIS-B radar targets and ADS-B out) equipped planes using either a 978 UAT or 1090-ES transponder. Day or night, you can "see" traffic on ADS-B long before you would ever be able to "see" the traffic with your eyes. I'm not concerned with traffic on the GPS navigator, since I have a tablet mounted on the tablet that has far better resolution than the screen on the GPS. Using my panel-mounted and knee board tablets, I can have weather and traffic super-imposed on the enroute chart with a geo-referenced instrument approach in real time on both displays.
 
Wait young grasshopper, wait
 
I have a GDL 39R receiver (the installed version, not the portable) and display ADS-B IN traffic on an Area 660, using the 660 internal GPS receiver with its external GPS antenna. For ADS-B OUT, I'm using the GDL 82 UAT and my existing GTX 327 Mode C transponder. This is an inexpensive ADS-B solution that works well if you're not going to fly in Class A airspace and limit your flying to the U.S. and the Bahamas.
 
We put the Appero Stratus w/internal GPS receiver in the Pawnee. We do not need an IFR capable gps navigator in the Pawnee. Works great to satisfy the ADS-B requirement. For my personal portable IN data, I have the STRATUX with dual antennas. I set it up on top of my flight bag in the back seat of Cessna and DA-40 rentals and have no issues on reception and WiFi to my iPad for data display.
 
chemgeek said:
Here are some sources to read:

https://airfactsjournal.com/2013/01/ads-b-101-what-it-is-and-why-you-should-care/
https://www.aopa.org/go-fly/aircraft-and-ownership/ads-b

Briefly, you will typically have one of two ADS-B OUT frequencies (978 or 1090) and may have 1090 (ES), 978 (UAT), or dual link (both ES and UAT) IN. Any ADS-B installation requires a WAAS GPS source, either from an approved panel unit (e.g. GNS, GTN series) or a dedicated unit that accompanies or is built in to the ADS-B device. If you have multiple GPS devices it is sometimes possible to share a GPS antenna, but is usually not recommended.

FYI, the GPS antenna is only for GPS reception, and is typically on the top of the aircraft. It is usually a hockey puck shaped unit. The 1090 and/or 978 MHz signals pass through your L-band (transponder) antenna, which is typically on the bottom of your aircraft, but you can also install additional antennae for better reception ("diversity" option). (This is for permanently installed units, not portable ones.)

What do the various frequencies do? You broadcast your position on your OUT frequency (UAT or ES, typically). You can receive traffic information on your IN frequencies (UAT, ES, or dual). If you are UAT IN only, you can see UAT equipped aircraft directly, 1090 ES equipped aircraft indirectly through ground rebroadcast on UAT, (ADS-R) and non-equipped Mode A/C aircraft via TIS-B ground rebroadcast of their radar position. If you are 1090 ES IN only, you can see 1090 ES traffic directly, UAT traffic via ground rebroadcast via 1090 ES, and Mode A/C only aircraft via TIS-B ground rebroadcast of radar position. If you are dual link, you can see both UAT and 1090 ES aircraft directly, and Mode A/C aircraft via TIS-B ground rebroadcast of radar position. Weather products (FIS-B) come only through UAT. I think this is all correct. Confusing, but it basically works really well.

So, as an example, I have a GNS-430W and decided to install an NGT-9000 1090ES OUT and dual-link IN unit. The NGT-9000 has its own WAAS unit built in, so I hooked that up to a second GPS antenna topside. The NGT-9000 pulls altitude info from my blind encoder, and broadcasts my position on 1090 ES. I receive traffic information directly from both UAT and 1090 ES frequencies, and TIS-B for Mode A/C aircraft. I also get weather (FIS-B) via UAT. In my case, a shared GPS antenna was NOT recommended. I am still using my previous L-band (Transponder) antenna on the bottom of the airplane. I did not opt for the "diversity" option.

A GDL-82 uses your existing transponder to obtain squawk code and pressure altitude, and broadcasts that information along with your GPS position on the UAT frequency. I don't think the GDL-82 cares what transponder you have as long as it is Mode C compatible and is working properly. All ADS-B solutions require an approved WAAS GPS data source to function. The GDL-82 itself is an approved source.

Cheers, and good luck. It's a bit of a morass to figure out how you would like to comply.
Click to expand...
Thanks @chemgeek !!!! I have to read it again but its making more sense now.

So when i am sitting at home (far away from a ADSB ground based xmtr) and receive traffic its either direct from a plane with a 1090ES xpdr which is encoding it GPS position along with altimeter, etc. Or its from a plane equiped with UAT ADSB out, broadcasting its position periodically. Question: Does the 1090ES transponder send out data all the time like ADSB out or onky when swept by radar and responding.?

Since were not sure yet regarding a RNAV capable navigator, it would seem that we will need a ADSB out solution with its own WAAS GPS and hence why i asked about the GDL82. Now lets say during the process we wanted to update to a 1090ES transponder (we live close to Canada and might try fly there). Can we buy a 1090ES transponder, perhaps used or yanked out when someone put in a Garmin 345 and then feed it GDL82's WAAS GPS. That would seem to get us compliant and as electronically visble as possible.

And it sounds like thru some complicated handling, even our unequiped plane with its mode c transponder can show up on others ADSBin traffic displays as long as an ATC radar is sweeping it and adding it to the ADSB rebroadcast. But you can only see that traffic if you can also recieve a ground station?
 
Actually you can get a GTX-345 with internal GPS source today, and later upgrade to WAAS GPS if that's your path. No need for GDL82 when you have a GTX-345 or 335.

The GPS WAAS antenna for GTX 345 can be reused for your future GPS.
 
Sinistar said:
Thanks @chemgeek !!!! I have to read it again but its making more sense now.

So when i am sitting at home (far away from a ADSB ground based xmtr) and receive traffic its either direct from a plane with a 1090ES xpdr which is encoding it GPS position along with altimeter, etc. Or its from a plane equiped with UAT ADSB out, broadcasting its position periodically. Question: Does the 1090ES transponder send out data all the time like ADSB out or onky when swept by radar and responding.?

Since were not sure yet regarding a RNAV capable navigator, it would seem that we will need a ADSB out solution with its own WAAS GPS and hence why i asked about the GDL82. Now lets say during the process we wanted to update to a 1090ES transponder (we live close to Canada and might try fly there). Can we buy a 1090ES transponder, perhaps used or yanked out when someone put in a Garmin 345 and then feed it GDL82's WAAS GPS. That would seem to get us compliant and as electronically visble as possible.

And it sounds like thru some complicated handling, even our unequiped plane with its mode c transponder can show up on others ADSBin traffic displays as long as an ATC radar is sweeping it and adding it to the ADSB rebroadcast. But you can only see that traffic if you can also recieve a ground station?
Click to expand...

The whole point of ADS-B is to report your position to ATC and other aircraft without the need for radar, every few seconds or so.

The GDL-82 sits between your transponder and your L-band antenna, and interrogates you transponder for squawk code and pressure altitude, and then broadcasts that info on UAT. Putting in a different transponder wouldn't change anything. If you replace your transponder with a 1090ES with WAAS source, you don't need the GDL-82 and I'm not sure how it could output the GPS data as it's not designed to do that. The GDL-82 is a kind of kludge to make a mode C transponder ADS-B compliant. A 1090ES transponder will already be compliant with an approved WAAS source. You could likely reuse the GPS antenna with your 1090ES unit.

And yes, you are correct that ADS-B equipped traffic can only see Mode A/C aircraft if ADS-B aircraft are receiving TIS-B from a ground station. In my hilly parts I start getting both TIS-B and FIS-B at 1500-2000 AGL.
 
Adding to Chemgeek.... You want ADS-B both In and Out. Once you fly with ADS-B it's very hard to ever fly without it again. The situational awareness for traffic is unparalleled, and weather is very helpful for that look ahead of you.

There are 3 method to achieve both In & Out:

One - Install an ADS-B In & Out transponder. This is the optimum pick.
  • New transponder
  • 1090 mhz global standard
  • Your position data is transmitted at full power - 240 watts
  • ADS-B (FIS-B) data receiver is internal to transponder, panel powered
  • ADS-B received with an external antenna (greater reception)
  • A big one: Only option FAA approved to display ADS-B data on your panel GPS or display
  • Reduced clutter in the cockpit; no external receiver stuck or stacked somewhere with power cables strung across the panel area
  • Most dual-link 1090MHz and 978MHz UAT ADS-B In
  • Most popular choices are GTX-345, Lynx 9000

Two - Install an ADS-B Out transponder w/an uncertified external appliance to receive ADS-B (FIS-B) data
  • New transponder
  • 1090 mhz global standard
  • Your position data is transmitted at full power - 240 watts
  • ADS-B (FIS-B) data is receiver is NOT certified and cannot display data on a panel mounted GPS (If you don't have a capable GPS now, you will at some point)
  • Some are dual-link 1090MHz and 978MHz UAT ADS-B In
  • Popular choices with internal WAAS position sources: GTX-335, Stratus ESG, King KT-74

Three - Pair your exiting transponder to an ADS-B Out transmitter
  • Use your existing legacy Mode C or S transponder
  • USA only 978 mhz with 18,000 ceiling (not a big deal for most GA planes)
  • Intercepts your current transponder signal and rebroadcasts your current squawk code as part of the ADS-B data packet
  • Position data transmitted 18-40 watts (most models)
  • Like Method Two, external uncertified receiver needed for ADS-B In
  • Lowest cost for compliance
  • Popular choices: GDL-82, Skybeacon, SkyTrax100, FreeFlight Rangr TXL
Garmin's GDL-88 has a WAAS position source and ASD-B in/out, and it connects with a compatible transponder. It's no longer a popular solution as it costs the same as a Method One solution above.

People have strong passions about what's best for them. Some have near theological passions for or against particular vendors.

For me, I got tired of using an external receiver like the Stratus 2 or similar. When power is low an external power cable is needed and adds to cockpit clutter. The GTX-345 or Lynx 9000 is solution I thought added the greatest resale value to the aircraft and was a 20 year solution.
 
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I like the option of having AHRS on an external power source....along with the ADS-B "in" functions.
 
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