Tracking far more planes than shown on Map---why??

[Jerry H. Prado]

I am running rtl1090 along with VirtualRadar. Everything seems to be working well. The only thing I don't understand is why I show 2x or 3x the number of aircraft in my Tracking list while only some of the AC are depicted graphically on the map. I have verified that I have no filters active. I have also zoomed out 400 miles..same thing..Any ideas?

 

[Richard Lee]

In the USA, most planes aren't sending a full ads-b (with lat and long).

http://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes

They only squawk ID and altitude, but RTL1090 decodes and lists those planes too.
I'm using RTL1090 B:153 and you can Surpress No Position Flights in the table.
But that data is sent to your VRS and those planes will show up in it's table..

It might seem useless to have that limited data, but it can be used with airport radar to locate and ID the plane.
It can also be used with Mlat.. http://www.multilateration.com/surveillance/multilateration.html
to get a pretty good location of the plane too..

PS: I'm just learning this stuff too. So I might be wrong on some of the details..

 

[Jerry H. Prado]

Thanks Richard,
I continue to research this issue. I am a veteran of the cellular world and to software engineering in general. Here is what I think that is happening:
1. The ADS data is multi sourced
2. There is ADS data that is transmitted by planes, via their ADS/GPS receivers feeding our transponders, and transmitting .
3. There is data originated from base stations that are interfaced with the TIS
4. Using a typical low-end antenna, as supplied with these SDR dongles, we hear aircraft only
5. Absent the base station data, we get just the AC data
Possible solutions:
a. Achieve better line of site to the closest controlled airspace airport
b. Use a real ADS-B Antenna, tuned to 1090.00

I too am new to this..so I welcome all knowledge.
Jerry Prado
Design Engineer, Samsung Mobile
KC5LON

 

[Richard Lee]

From reading pdfs here and there, I know there are FAA ground stations that listen on 1090 Mhz and send the data the FAA data centers.
So the local airport can get a heads up while planes are still out of range of the 1090 antennas at the airport..

What I'm doing here, is listening to the local planes around the greater Boston area, and sending the data back to PlaneFinder
so they can display the data on their website. http://planefinder.net/

I have a nice 1090 antenna installed. (On loan from PlaneFinder).
My dongle is doing a pretty good job, but I hope to have more professional equipment soon..

Wow, it's way after my bedtime..

73,
Rich

PS:
Just got the shipping info, the 'professional equipment' is on it's way.
Hope to have it running in a few days.

I see you are from north of Dallas, I'll bet you have a ton of air traffic around there!