Question For Those of You w/ ADSB In & Out...

netsurfr

netsurfr

Pre-takeoff checklist
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Jose
So those of you who have already installed ADSB In and Out capability could you share at what altitude above the ground you typically LOOSE ADS-B Traffic?

Also - Have you experience pockets with no reception to ADSB ground stations while flying around up at altitudes?

I'm toying w/ adding ADSB IN/OUT primarily for traffic and since the air-to-air benefits of this won't really materialize till most/all planes are compliant I'm curious how effective ADSB traffic is especially during takeoffs/landings/approaches.

Thanks!
 
I get ADS-B data on the ground at FTG...

Traffic data depends on two major things: radar coverage and ADS-B tower coverage so if you're near a radar site and an ADS-B site you will have great coverage.

If you're in the great wastelands of the west then coverage may not be so good. That said, I've had UAT traffic while approaching Riverton, Wyoming (traffic was going to Lander - we talked on CTAF after I made my 10 mile call). On the other hand, I've been invisible to center below 10,000' over western Kansas/eastern Colorado - no radar=no ADS-B traffic. For some reason no one seems to concerned with fixing radar problems out there...

There is a third, minor, thing which is aircraft with 1090ES which you will always receive if you have 1090 ADS-B in. Watching airliners at 30,000 feet is mildly entertaining on long cross country flights.
 
Thanks. I too fly out of an airport w/ radar & adsb ground station nearby and there no mountains around here to block reception/radar but still trying to assess when adsb broadcast traffic drops off. Wish there was a map that showed VERTICAL coverage of both radar and adsb.


Clark1961 said:
I get ADS-B data on the ground at FTG...

Traffic data depends on two major things: radar coverage and ADS-B tower coverage so if you're near a radar site and an ADS-B site you will have great coverage.

If you're in the great wastelands of the west then coverage may not be so good. That said, I've had UAT traffic while approaching Riverton, Wyoming (traffic was going to Lander - we talked on CTAF after I made my 10 mile call). On the other hand, I've been invisible to center below 10,000' over western Kansas/eastern Colorado - no radar=no ADS-B traffic. For some reason no one seems to concerned with fixing radar problems out there...

There is a third, minor, thing which is aircraft with 1090ES which you will always receive if you have 1090 ADS-B in. Watching airliners at 30,000 feet is mildly entertaining on long cross country flights.
Click to expand...
 
netsurfr said:
Thanks. I too fly out of an airport w/ radar & adsb ground station nearby and there no mountains around here to block reception/radar but still trying to assess when adsb broadcast traffic drops off. Wish there was a map that showed VERTICAL coverage of both radar and adsb.
Click to expand...

How low do you normally fly?
 
netsurfr said:
Thanks. I too fly out of an airport w/ radar & adsb ground station nearby and there no mountains around here to block reception/radar but still trying to assess when adsb broadcast traffic drops off. Wish there was a map that showed VERTICAL coverage of both radar and adsb.
Click to expand...

The data I get on the ground includes traffic in the pattern - departing aircraft show up on the upwind.
 
The first condition that must be met is that the mode A/C target aircraft has to be detected by radar. If you know this altitude, it is very likely you will also have line of sight to an ADS-B GBT. You can ask a controller how low they can pick your transponder up at to gage where this will be near a particular airport.
 
Garmin is also marketing what they call Diversity Antennae - mounted top and bottom of aircraft and they seem to claim this allows taxiing traffic to be seen while on the ground...... At least that's my take on their verbiage
 
Normally fly high enough (MEA) so that's not the problem but what I'm trying to determine is if ADSB rebroadcast traffic is effective for landings and/or takefoffs enough that it makes sense to bite the bullet and install ADSB out/in now. I was originally thinking TAS for traffic but it's a tough pill to swallow to have TAS installed for $13K and still not meet the ADSB mandate and also knowing that by 2020 ADSB traffic will work like/better than TAS does today (assuming plane-to-plane).

Henning said:
How low do you normally fly?
Click to expand...
 
Yes and this is what I've been googling lately to see if I could find graphical or textual representation of vertical radar coverage in the US but not really finding it so thought I'd ask for personal experience from those who have installed the adsb in/out already.

John Collins said:
The first condition that must be met is that the mode A/C target aircraft has to be detected by radar. If you know this altitude, it is very likely you will also have line of sight to an ADS-B GBT. You can ask a controller how low they can pick your transponder up at to gage where this will be near a particular airport.
Click to expand...
 
Thanks that's what I've been assuming. Do you have ADSB out as well? If so are you happy w/ the traffic info you're receiving?

dell30rb said:
Typically my stratus picks up traffic + weather at 3-400 AGL
Click to expand...
 
netsurfr said:
Yes and this is what I've been googling lately to see if I could find graphical or textual representation of vertical radar coverage in the US but not really finding it so thought I'd ask for personal experience from those who have installed the adsb in/out already.
Click to expand...

I have the locations charted in a .kml file for 508 of the 634 ADS-B GBT. You are welcome to download them at https://dl.dropboxusercontent.com/u/58910037/user_waypoints.kml and view them on Google earth by clicking on the file. They may also be downloaded to ForeFlight as user waypoints.

I still need to get the locations of the ones installed in the Utah, ND, SD, Wyoming, and Montana areas if anyone wishes to capture them with a Stratus/Foreflight system.
 
wrbix said:
Garmin is also marketing what they call Diversity Antennae - mounted top and bottom of aircraft and they seem to claim this allows taxiing traffic to be seen while on the ground...... At least that's my take on their verbiage
Click to expand...

The surface ADS-B is available only at the larger airports, mostly the Class B airports. I think there are 35 airports that have this capability. For my use, it does not justify the extra expense of the top antenna and the feature for diversity although it probably only adds $1000 to the installation costs, I would never take advantage of it. For diversity capability with the GTX330ES, the price more than doubles the installation costs, list $3,995 to over $8,600.
 
Wow. Very Cool. Thanks! So I take it these are all (except for Wyoming & Montana) radar sites?


John Collins said:
I have the locations charted in a .kml file for 508 of the 634 ADS-B GBT. You are welcome to download them at https://dl.dropboxusercontent.com/u/58910037/user_waypoints.kml and view them on Google earth by clicking on the file. They may also be downloaded to ForeFlight as user waypoints.

I still need to get the locations of the ones installed in the Utah, ND, SD, Wyoming, and Montana areas if anyone wishes to capture them with a Stratus/Foreflight system.
Click to expand...
 
Out of Conway, Ar I start picking up traffic around 800 ft AGL. This is in rural AR for the most part. No service on ground.

At 3500 and above, I have yet to loose broadcast coverage anywhere in AR.
 
Yes what I've read is that diversity antennas for GA is unnecessary but now you make me think of another question....

Down the road when most/all planes are broadcasting 978/1090 out will those signals be received if a plane is on the ground? In other words if I'm on the ground (adsb out and in equipped and single antennae on the top) will I see other planes in the pattern and/or will they be able to see me?


John Collins said:
The surface ADS-B is available only at the larger airports, mostly the Class B airports. I think there are 35 airports that have this capability. For my use, it does not justify the extra expense of the top antenna and the feature for diversity although it probably only adds $1000 to the installation costs, I would never take advantage of it. For diversity capability with the GTX330ES, the price more than doubles the installation costs, list $3,995 to over $8,600.
Click to expand...
 
Good to know. Thanks!

Unit74 said:
Out of Conway, Ar I start picking up traffic around 800 ft AGL. This is in rural AR for the most part. No service on ground.

At 3500 and above, I have yet to loose broadcast coverage anywhere in AR.
Click to expand...
 
Well, here's what Garmin says re Diversity:
Available antenna options allow the performance of the GDL 88 to be optimized for any type of aircraft. For optimal performance, a diversity antenna version with both top- and bottom-mounted antennas enhance the detection of traffic both above and below, and works to minimize radio blind spots caused by the wings or fuselage during aircraft maneuvering. This is especially useful in maintaining optimal reception of ADS-B weather and traffic during ground operations. A basic bottom-mount antenna version is also available as a more cost-effective alternative.

Sounds to me like bottom mount is standard so as to talk to/listen to the ADS-B station in flight, top to allow low altitude/ground reception.
 
I get traffic on the ground, and usually weather shortly after my wheels come up. Never lost it in-flight.
 
netsurfr said:
Wow. Very Cool. Thanks! So I take it these are all (except for Wyoming & Montana) radar sites?
Click to expand...

No, ADS-B GBT sites. I keep using the term GBT because it is the acronym for the ADS-B ground stations (I get tired of typing Ground Based Transceiver which is what it stands for). Sorta like nobody uses Very High Frequency Omni-directional Radio-range instead of VOR.
 
Ted DuPuis said:
I get traffic on the ground, and usually weather shortly after my wheels come up. Never lost it in-flight.
Click to expand...

I doubt it is TISB unless the airport is one of the few with Surface ADS-B, in which case you would also get weather on the ground. You are probably receiving ADS-B Out equipped aircraft.
 
wrbix said:
Well, here's what Garmin says re Diversity:
Available antenna options allow the performance of the GDL 88 to be optimized for any type of aircraft. For optimal performance, a diversity antenna version with both top- and bottom-mounted antennas enhance the detection of traffic both above and below, and works to minimize radio blind spots caused by the wings or fuselage during aircraft maneuvering. This is especially useful in maintaining optimal reception of ADS-B weather and traffic during ground operations. A basic bottom-mount antenna version is also available as a more cost-effective alternative.

Sounds to me like bottom mount is standard so as to talk to/listen to the ADS-B station in flight, top to allow low altitude/ground reception.
Click to expand...

I have not had any issue receiving ADS-B weather on the ground at my airport. There is a GBT on the field, although it is not a surface tier tower, but rather a low altitude tier tower. If you operate at one of the class B airports, it would be useful. Interesting to note, most ADS-B 1090ES installations in GA aircraft do not use diversity. The KT74, Trig, and Avidyne units don't support diversity. The GTX330ES does, but it sure is expensive.
 
A lot of this is probably equipment specific. Does your ADSB in gear receive ADSB on 1090 and 497Mhz direct or rely on the rebroadcast? When I was handling this at airline level, all of our mode S transponders would squit on the ground (top antenna only). Still no way to see a UAT airplane unless you had an onboard ADSB receiver that listened to 497MHz or got it from the FAA reproadcast. I always assumed that relying on it on the ground, at best you would reliably see some, for that reason.
 
kontiki said:
A lot of this is probably equipment specific. Does your ADSB in gear receive ADSB on 1090 and 497Mhz direct or rely on the rebroadcast? When I was handling this at airline level, all of our mode S transponders would squit on the ground (top antenna only). Still no way to see a UAT airplane unless you had an onboard ADSB receiver that listened to 497MHz or got it from the FAA reproadcast. I always assumed that relying on it on the ground, at best you would reliably see some, for that reason.
Click to expand...

In most of the current air carrier aircraft systems installed, they are not compliant and use TSO C166a (called version 1). Some of the newer air carrier aircraft have the compliant version TSO C166b (called version 2). In either case, these are mostly ADS-B Out and do not have any ADS-B In capability. The version 1 and version 2 systems are handled differently by a GBT. Version 2 systems include two bits of data that are broadcast to indicate the ADS-B In receive capability. Version 1 systems do not have these bits defined. For a version 2 system, a GBT determines if and on what frequency to broadcast traffic services based on the settings of the client aircraft. If the 978 MHz bit is on, then traffic services are broadcast on 978 MHz; if only the 1090 MHz bit is on, then traffic services are broadcast on 1090 MHz; and if both bits are off (the airliner case) then traffic services are not broadcast. Since with a Version 1 system, the GBT can't determine if the client aircraft has any ADS-B In capability or what frequency it receives, traffic services are broadcast on 1090 MHz (most airliners today fall into this category). The version 1 traffic services will go away in 2020 and traffic services will only be broadcast for appropriate Version 2 systems.

A version 1 system on an air carrier aircraft will trigger TISB traffic targets being broadcast on 1090 MHz. A version 2 system installed on an air carrier aircraft is not likely to trigger TISB on any frequency. So to receive these, the ADS-B portable receiver will be a dual frequency unit that can receive on both frequencies. A dual frequency receiver is a defacto standard for portables, although the earlier units are single frequency (UAT 978 MHz). The Stratus 1 is single frequency, the Stratus 2 is dual. The GDL39 is dual frequency.
 
Its been a couple years so some of my details are rusty, but the last package I released took that fleet to DO-260a (then the latest and greatest ADS-b out). Details for that project were finalized before the final rule, which required DO-260B. We had no ADS-b in just an upgrade path via a hybridized TCAS processor that had hardware support to support ads-b controls and displays. At that time, UPS were the only ones trying to use ADS-b in. Airbus was interested too. UPS was going for merging and spacing and ADS-B assisted visual approach. Airbus was looking at en-trail passsing. I don't know where it all is now.

I don't see why you'd need the bit, seems like the gear would know what frequency it heard the data on. I never found time to dig into UAT, are you saying the UAT transciever both transmits and receives on 978?
 
kontiki said:
Its been a couple years so some of my details are rusty, but the last package I released took that fleet to DO-260a (then the latest and greatest ADS-b out). Details for that project were finalized before the final rule, which required DO-260B. We had no ADS-b in just an upgrade path via a hybridized TCAS processor that had hardware support to support ads-b controls and displays. At that time, UPS were the only ones trying to use ADS-b in. Airbus was interested too. UPS was going for merging and spacing and ADS-B assisted visual approach. Airbus was looking at en-trail passsing. I don't know where it all is now.

I don't see why you'd need the bit, seems like the gear would know what frequency it heard the data on. I never found time to dig into UAT, are you saying the UAT transciever both transmits and receives on 978?
Click to expand...

The two bits are used to determine which frequencies the aircraft can receive ADS-B In with. They do not have to be the same as the one used for broadcasting ADS-B. The GBT traffic services of ADSR and TISB are conditional based on there being a client in the service volume. If the client indicates it does not have ADS-B In capability on either frequency, then the GBT will not provide the traffic services. Particularly for 1090ES, it is more congested and this reduces unnecessary 1090ES broadcasts that the client can't receive anyway. If the client indicates it has 978 MHz receive capability, then TISBl traffic services are only broadcast on 978 MHz. If the client indicates it has ADS-B In capability for both frequencies, then the ADS-R service is not provided as the aircraft can receive these targets via air to air and have no need of the ADSR. If only a single frequency is indicated as being available, then both ADSR and TISB use that frequency.

The In and Out can be mixed and matched as they are very loosely coupled. There are mode S transponders with ES and a built in 978 MHz receiver on the way to the market, sometime in 2015. This can make sense for GA because the benefits of the system are in the UAT In capability with both weather and traffic.

The Garmin and several other vendors have made dual frequency receivers a defacto standard, such as the GDL88, GDL84, GDL39, Stratus 2, and so on.

Yes a UAT transceiver broadcasts and receives on 978 MHz although these functions can be packaged separately.
 
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