ADS-B tower types for traffic

[dans2992]

So, I understand that the weather products broadcast by “high” “medium” and “low” ADS-B towers differ.

Does traffic broadcast by these different types of towers also differ? Why is it that larger airports often have more than 1 ADS-B tower on the field? Do all towers do both 978/1090?

Is there a technical document that describes precisely how this all works?

 

[dell30rb]

978 UAT is the frequency for weather +traffic broadcast, ads-b in. If you are below 18,000ft you can use an ads-b out transmitter on this frequency.

1090es is the ads-b out frequency for higher traffic. If you fly above 18k, you need an ads-b out transmitter that will transmit on these frequencies. Most of the common transponders do.

https://www.faa.gov/nextgen/equipadsb/capabilities/ins_outs/

If you already have a dual band ads-b in receiver like the $200 foreflight scout, stratus etc... then adding an appropriate ads-b out does two things for you. #1 it triggers TIS-B for your immediate area, so any non-ads b traffic (planes who have not updated yet) will be rebroadcast to you. and #2 it allows other aircraft with ads-b in to see a more accurate position of your aircraft.

The biggest benefit for us after 2020 IMO is going to be in the uncontrolled airport traffic pattern, or any areas with no radar coverage (mountain passes etc...) You will be able to see an almost instantaneous traffic picture of any aircraft in the pattern, on the runway or taxiway.. with no atc radar services needed.

 

[denverpilot]

https://www.faa.gov/nextgen/programs/adsb/ICM/ - coverage by altitude.

 

[dans2992]

Yes. I understand this.

I’m trying to figure out, in a metro area with multiple towers, which ones will be broadcasting the most TIS-B traffic.

I’m building a receiver to detect the traffic, plot it in a map, etc.

 

[denverpilot]

Yes. I understand this.

I’m trying to figure out, in a metro area with multiple towers, which ones will be broadcasting the most TIS-B traffic.

I’m building a receiver to detect the traffic, plot it in a map, etc.

Why not just try to receive all of them? It's doubtful in most metros if you'll receive more than a couple at ground level, unless you install extreme low loss feedline, probably a mast mounted pre-amp, and have a very high quality receiver overall to reach out and hear the ones further away with a directional antenna.

But the easiest way to answer the question in a "metro" would be to simply drive closer and copy it for a while. You'd know what every one of them actually transmits in the area in a couple of days.

Also it'd be cost-effective and what not, but a little more code and networking setup (well, ssh... yawn...), but getting a buddy to put a crappy cheap receiver nice and close to any you can't hear, and just shipping the raw data over to your system that's processing it and making the maps, is another simple solution... it's effectively what the bigger web sites are doing nationwide to get their ADS-B stuff that is filtered out by FAA, after all. FlightAware of course, leading that pack...