ADS-B traffic oddity

Indiana_Pilot

Indiana_Pilot

Line Up and Wait
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Nov 2, 2013
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Connersville, IN
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Flying "B"
So I am very familiar with how ADS-B works and also the limitation of Foreflight/Stratus 2 without it. I have a portable ads-b transmitter I have been using until I have a certified install put in.

Anyway.. I flew about a 100 mile flight without the transmitter and only the Stratus 2..
I was surprised that was receiving TIS-B traffic 99% of the time. I verified this by checking the Stratus update interval (reporting "just Now")

I understand that I can receive TIS-B traffic when I am around another aircraft that is transmitting.. I can assure you that I did not see any other aircraft on the screen within 30 NM most of the time..

I can always tell a clear difference when I am not transmitting ads-b out and when I am, so I know the difference in traffic volume..

What gives? Why am I receiving TIS-B traffic when I technically should not be ??
 
I confused. Why would transmitting ADS-B out messages or not mean anything wrt receiving TIS-B messages?
 
TIS B traffic is only received if you are transmitting or around another aircraft that is.. this is different that what comes directly from the aircraft.. TIS B is a rebroadcast from ground stations that show all traffic on radar.. ads b, mode c, etc ..
 
I have recieved traffic alerts when away from other aircraft,I'm thinking some stations are re broadcasting all traffic.
 
Firefighter_324 said:
So I am very familiar with how ADS-B works and also the limitation of Foreflight/Stratus 2 without it. I have a portable ads-b transmitter I have been using until I have a certified install put in.

??
Click to expand...

I would have thought you'd need some kind of FCC approval/license to operate a portable transmitter in that band. Are you simulating Mode S or a UAT transmissions?
 
It's UAT and I don't believe you need any type of FCC license for that.. it's one of those WX Guard UAT transmitters..
 
I agree with that but the rebroadcast only focuses the traffic displayed within 30nm I belive.. so there would have to be an ads-b aircraft close to me for me to piggy back of their signal.. meaning I would see their 978/1090 signal direct and not the rebroadcast tis-b traffic.. I will look at the article that explains this in detail for you in the morning.. simply put I should not have been seeing the tis b rebroadcast..
 
Firefighter_324 said:
After I think about it vhf aircraft and Transponder radios don't require a license ...
Click to expand...

Aircraft radios require a station license but not an operator's license.

From FCC regs:

87.18 Station license required.
(a) Except as noted in paragraph (b) of this section, stations in the aviation service must be licensed by the FCC either individually or by fleet.
(b) An aircraft station is licensed by rule and does not need an individual license issued by the FCC if the aircraft station is not required by statute, treaty, or agreement to which the United States is signatory to carry a radio, and the aircraft station does not make international flights or communications. Even though an individual license is not required, an aircraft station licensed by rule must be operated in accordance with all applicable operating requirements, procedures, and technical specifications found in this part.

Bob Gardner
 
Firefighter_324 said:
So I am very familiar with how ADS-B works and also the limitation of Foreflight/Stratus 2 without it. I have a portable ads-b transmitter I have been using until I have a certified install put in.

Anyway.. I flew about a 100 mile flight without the transmitter and only the Stratus 2..
I was surprised that was receiving TIS-B traffic 99% of the time. I verified this by checking the Stratus update interval (reporting "just Now")

I understand that I can receive TIS-B traffic when I am around another aircraft that is transmitting.. I can assure you that I did not see any other aircraft on the screen within 30 NM most of the time..

I can always tell a clear difference when I am not transmitting ads-b out and when I am, so I know the difference in traffic volume..

What gives? Why am I receiving TIS-B traffic when I technically should not be ??
Click to expand...

There are two bands received by the Stratus 2, the 1090 MHz one for 1090ES and the 978 MHz one for UAT. The just now only indicates that a traffic report within line of sight has just been received. It could be from an aircraft 100 NM away or a TISB from any ground station you are receiving at the time. It does not mean that you are receiving TISB service or that any of the traffic is relevant to you. It is typical that once in flight you will see these indications. In fact, when you are on the ground you will see 1090ES from airliners 30000 feet + overhead. UAT is less likely on the ground because the aircraft that broadcast using UAT fly lower and there are fewer of them. Once airborne, you have greater line of sight range and also receive far away TISB.
 
Sorry but you are incorrect.. without ads-b out you won't receive tis b traffic.. tis b traffic I'd not air to air it's rebroadcast from the ground.. not related to weather or any other data other than rebroadcast traffic
 
Firefighter_324 said:
Sorry but you are incorrect.. without ads-b out you won't receive tis b traffic.. tis b traffic I'd not air to air it's rebroadcast from the ground.. not related to weather or any other data other than rebroadcast traffic
Click to expand...

Not sure who you are referring to, but the operative letter in this technology is the B for Broadcast. Anyone with a receiver and line of sight to the ground station WILL RECEIVE the TISB. Without ADS-B Out, the GBT will not generate a TISB on your behalf, but anytime a TISB is Broadcast, all receivers in direct line of sight will receive it as it is not addressed to any aircraft.
 
How is a good way to tell you are receiving all the traffic then? Is there no good indication on Foreflight ?
 
Firefighter_324 said:
How is a good way to tell you are receiving all the traffic then? Is there no good indication on Foreflight ?
Click to expand...

You never receive "all of the traffic" because of the limitations of the system. However, to receive the best possible view of the traffic, the GBT needs to receive the ADS-B Out from your aircraft and determine that your aircraft is to be treated as a client for the TIS-B service. ForeFlight does not have a positive indication of your aircraft being treated as a Client. The best you can do is to infer that you are receiving the TIS-B service by traffic reports that are nearby to your position, this is inside your hockey puck (1 NM radius and +/- 3500 feet).

Stratus/ForeFlight provides an indication that own ship has been detected. This is indicated in More>Device>Stratus 2 below the indication of the three Traffic Update status lines (978/UAT, 1090, and TIS-B ). Assuming you have ADS-B Out on board, you should see your own N number displayed next to Ownship. If you see the message "Not Detected" next to own ship, this indicates that no ADS-B Out is being detected. If it does show your N number, then you can tap on it and see what your ADS-B Out system is broadcasting. To see all of the data, it doesn't fit on one screen, you have to slide the view down to see the remaining data.

If Skyguard is being used as your portable ADS-B Out system, just be aware that this unit will "cloak" your position on an aircraft with a certified system because certified systems will ignore non certified systems in accordance with meeting the TSO requirements. The Skyguard will be accepted by the GBT as a client and it will provide TIS-B service for such a client, but any aircraft that is treated as a client has TIS-B suppressed for own ship. So with your Skyguard turned off, a certified system will see your TIS-B, but once the Skyguard is turned on, your TIS-B target will disappear and your ADS-B target will be ignored.
 
Bummer thanks for the info.
I hope the price comes for a certified install soon. I think Appareo Is coming out with something cheaper later this year according to Sportys...
 
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