Garmin Portable ADS-B

John Collins said:
Agree with your analysis, to refresh your memory, assuming the client is in the middle of the hockey puck, the puck dimensions are +/- 3500 feet and with a 30 NM diameter for TISB. For ADSR, the dimensions are +/- 5000 feet and and 30 NM diameter.
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But... if ADS-R broadcasts are omnidirectional (are they, I don't know), wouldn't you pick up ALL the traffic that exists in all the "pucks" with an ADS-B OUT aircraft in them?

Put another way - if every puck in the ground station service volume had an airplane with ADS-B OUT at the center, would an airplane listening to ADS-R get the complete picture for the service volume?
 
TMetzinger said:
But... if ADS-R broadcasts are omnidirectional (are they, I don't know), wouldn't you pick up ALL the traffic that exists in all the "pucks" with an ADS-B OUT aircraft in them?

Put another way - if every puck in the ground station service volume had an airplane with ADS-B OUT at the center, would an airplane listening to ADS-R get the complete picture for the service volume?
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The 1090ES, depending on the power of the ground station (they have several tiers of power and services), the higher power units are broken into four directional segments. 1090 MHz is more congested as it is used by aircraft transponders which are triggered by ground radars and TCAS/TCAD units as well as the asynchronous mode S squitters and the ES of ADSB. Therefore, using the directional capability on 1090 MHz along with adjusting the transmit power are important to mitigate saturation on the frequency. Anytime the ground station determines that an eligible aircraft has identified that it has dual frequency receiver capability, it will receive the TISB on UAT and not via 1090ES, also as a means of mitigating the 1090 MHz congestion.
 
airguy said:
Slight clarification here - the traffic that is transmitted from the ground stations upward is receivable by all aircraft with the correct reciever (since it's a broadcast radio signal) - but the traffic described in that broadcast are only the targets within a certain "puck" of airspace - if I remember correctly it's 7 miles radius and 3500' above and below. Each aircraft that is using ADSB-OUT triggers the traffic in his "puck" of airspace to be included in the broadcast. If you ADSB-IN only and are 20 miles from that participating aircraft, you can recieve data about the traffic relevant to him, but it's not relevant to you. If you are flying formation with him then his traffic will also show up on your screen.

There might be 100 targets within a given piece of airspace, but if there is only one participating ADSB-OUT aircraft in that airspace and only 3 targets are in his "puck" of airspace, the broadcast only includes data for those 3 targets. The other 97 are see-and-avoid.
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So...to dumb it down a bit, what you're saying is it's like a few guys are all in a dark hanger, and only the guys in the ADSB-OUT list have flashlights. Everyone can see what the ADSB-OUT guys see, but nobody can see anything around the ADSB-IN guys. If an ADSB-OUT guy wanders over in my area, I can see what's in my area. Otherwise, I'm in the dark.

I spent 20 years in IT support. I'm a pro at dumbing **** down. :yes:
 
Rigged4Flight said:
So...to dumb it down a bit, what you're saying is it's like a few guys are all in a dark hanger, and only the guys in the ADSB-OUT list have flashlights. Everyone near the guys with the flashlights can see what the ADSB-OUT guys see, but nobody can see anything around the ADSB-IN guys. If an ADSB-OUT guy wanders over in my area, I can see what's in my area. Otherwise, I'm in the dark.

I spent 20 years in IT support. I'm a pro at dumbing **** down. :yes:
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I think I fixed that for you...
 
One other question - are these messages from the ground station to the aircraft (ADS-R) specifically addressed to the aircraft in response to their ADS-B broadcast of their position? I know anybody else in "range" would see the message, but I get the impression it's a unique message addressed to a specific airplane, rather than a "here's the 12:05:03.1111 traffic report" broadcast.
 
Have forflight and am cosidering stratus, already use xm with my 496, nothing beats geo ref approach plates on forflight. However going to check out all options at osh
 
John Collins said:
The 1090ES, depending on the power of the ground station (they have several tiers of power and services), the higher power units are broken into four directional segments. 1090 MHz is more congested as it is used by aircraft transponders which are triggered by ground radars and TCAS/TCAD units as well as the asynchronous mode S squitters and the ES of ADSB. Therefore, using the directional capability on 1090 MHz along with adjusting the transmit power are important to mitigate saturation on the frequency. Anytime the ground station determines that an eligible aircraft has identified that it has dual frequency receiver capability, it will receive the TISB on UAT and not via 1090ES, also as a means of mitigating the 1090 MHz congestion.
Click to expand...

John, thanks for making this clear to us. I have a Monroy ATD-300+ and it can detect all traffic around me anywhere, even on the ground and in the Bahamas. What would be advantage of having ADS-B-in if my Monroy unit can do the job without all the in-out hassle.

José
 
TMetzinger said:
One other question - are these messages from the ground station to the aircraft (ADS-R) specifically addressed to the aircraft in response to their ADS-B broadcast of their position? I know anybody else in "range" would see the message, but I get the impression it's a unique message addressed to a specific airplane, rather than a "here's the 12:05:03.1111 traffic report" broadcast.
Click to expand...

ADSR is not addressed to a specific aircraft, but is generated on behalf of a specific aircraft when two or more ADSB equipped aircraft, on separate frequencies enter the same hockey puck of airspace. In other words it is a rebroadcast by the ground station of a specific aircraft's ADSB message on the opposite frequency when needed. If aircraft A is using UAT ADSB Out/In and aircraft B is using 1090ES for ADSB Out/In, and they are in each others hockey puck, then the ground station will duplicate (ADSR) any aircraft A ADSB position report on 1090ES message and any Aircraft B ADSB position report on UAT. Assuming that Aircraft A has a dual frequency receiver, it notifies the ground station of this configuration, therefore when Aircraft B sends a position report, the ground station will not generate an ADSR message on UAT, because the ground station assumes that aircraft A heard it on its 1090ES ADSB In receiver.
 
Piloto said:
John, thanks for making this clear to us. I have a Monroy ATD-300+ and it can detect all traffic around me anywhere, even on the ground and in the Bahamas. What would be advantage of having ADS-B-in if my Monroy unit can do the job without all the in-out hassle.

José
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The potential advantage is that with ADSB, you will get a position update every second instead of every 6 to 12 seconds. It will be able to provide a relatively precise distance and bearing as well as a track vector and can verbalize the traffic annunciation, traffic 10 O'Clock, one mile, high, descending. The Monroy depends on the target being within radar coverage, the same as the case for ADSB with radar mode C targets, but will see same frequency ADSB traffic regardless if they are in radio contact. With a dual frequency receiver, the ADSB equipped aircraft will see both frequencies, even when out of radar coverage. An active TCAS or TCAD has the potential of seeing more traffic, but it still depends on there being a transponder and it being on, in order for it to register. No system will see an aircraft without an electrical system.
 
John Collins said:
The potential advantage is that with ADSB, you will get a position update every second instead of every 6 to 12 seconds. It will be able to provide a relatively precise distance and bearing as well as a track vector and can verbalize the traffic annunciation, traffic 10 O'Clock, one mile, high, descending. The Monroy depends on the target being within radar coverage, the same as the case for ADSB with radar mode C targets, but will see same frequency ADSB traffic regardless if they are in radio contact. With a dual frequency receiver, the ADSB equipped aircraft will see both frequencies, even when out of radar coverage. An active TCAS or TCAD has the potential of seeing more traffic, but it still depends on there being a transponder and it being on, in order for it to register. No system will see an aircraft without an electrical system.
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The ATD-300 can detect mode S 1090MHz ES ADS-B and mode C traffic while being on the ground. I have seen this at Providenciales, Bahamas. But ADS-B-IN would not work on the ground for Mode C traffic since it needs to be in coverage of a ground UAT station. Is this correct? How would you know if the ADS-B-IN works before departure? At least with TCAS and Monroy I can check it on the ground with traffic in the pattern.

José
 
TMetzinger said:
I think I fixed that for you...
Click to expand...
Thanks!

What if I wasn't near someone that had ADSB-OUT. Would I be able to scroll my map and see aircraft in their area? I assume so, because since I don't have ADSB-OUT, nobody knows what area I'm in, anyways. Handled by the device that correlates my maps/data?

Can anyone with an iPad and an ADS-B device confirm/deny this? Not that it matters, really. I just like delving into the bits/bytes of how stuff works. :)
 
Piloto said:
The ATD-300 can detect mode S 1090MHz ES ADS-B and mode C traffic while being on the ground. I have seen this at Providenciales, Bahamas. But ADS-B-IN would not work on the ground for Mode C traffic since it needs to be in coverage of a ground UAT station. Is this correct? How would you know if the ADS-B-IN works before departure? At least with TCAS and Monroy I can check it on the ground with traffic in the pattern.

José
Click to expand...

If there is known traffic in the pattern that have a mode C transponder on, I would guess that with a Monroy you could check its operation on the ground, depending of course on a nearby TCAS interrogator. ADSB is not likely to see mode C targets in the pattern, unless the target is in radar coverage and the ADSB Out/In is within the service volume of the ground station. At my airport, we are fortunate and have an ADSB ground station on the field. Aircraft in the pattern will be able to be seen on the ground, until they descend below radar coverage which will occur at about 1000 MSL or 350 AGL. Until 2020, this will be a significant limitation on the ADSB system when all will be essentially required to comply with the mandate, then the vast majority of the aircraft will have both ADSB and a transponder. Nothing is foolproof, there will always be equipment failures, some aircraft won't equip as they don't need to fly into airspace where ADSB or a transponder are required, some aircraft won't have a power source, etc.

So if you know there is an airplane in the pattern and the Monroy doesn't detect it, is it a failure in your Monroy, or does the airplane in the pattern not have their transponder on, or it is broken, or one isn't installed or there doesn't happen to be a nearby TCAS equipped aircraft interrogating the aircraft?
 
Rigged4Flight said:
Thanks!

What if I wasn't near someone that had ADSB-OUT. Would I be able to scroll my map and see aircraft in their area? I assume so, because since I don't have ADSB-OUT, nobody knows what area I'm in, anyways. Handled by the device that correlates my maps/data?

Can anyone with an iPad and an ADS-B device confirm/deny this? Not that it matters, really. I just like delving into the bits/bytes of how stuff works. :)
Click to expand...

I am sure that depends on the design of the receiver. If the receiver can receive the ADSB message, it can display it, but many receiver designs will limit what data is passed on to the display and that can be just those nearby or no more than a particular limit, such as the nearest 8 or 30.
 
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