Lots of ADS-B coverage around CYYT but no MLAT data?

FlightAware ADS-B Flight Tracking
1

Hi,

I noticed a few MLAT compatible RPIs around CYYT and there does not seem to be any MLAT data showing up on the FlightAware system.

Is there something that is not being done correctly by those stations?

I noticed the the FlightFeeder at CYQX is not MLAT compatible. I am assuming that it will be upgraded at some point to do so?

Thanks,
Scott.

2

Around CYYT it just looks like not enough coverage. There are only the bare minimum for mlat (4 receivers) in that area. There is not all that much ADS-B traffic for synchronization and the receivers don’t look like they have great overlapping coverage. I looked at the server just now and only 3 had synchronized. There is a little mlat traffic being generated there, but not much.

They’re not synchronizing with your receiver because of the server layout; there is a server border that lies between your receiver and theirs, and the overlap region is not large enough to put you both on the same server. (basically, CYYT gets handled by the server that handles the north atlantic, your receiver gets handled by the server that handles most of eastern canada).

I’m not sure if it’s worth manually tweaking those regions, as looking at the receiver ranges I don’t think they can see the same aircraft that you do anyway.

FF support for mlat is in the works but I do not have an ETA.

3

Is there a reason that the server coverage could no overlap by the range of a reasonably configured receiver, 200Km - 300km

4

There is overlap, IIRC it is currently about 60 miles which is enough to handle most cases.

The problem with increasing the overlap much more is that some of the server regions are not much larger than the overlap size in dense areas anyway. To subdivide a (triangular) region it gets split in 4 and the overlap added. If the overlap is too large, that doesn’t actually reduce the load the region needs to handle. It could be smarter about this but the current setup actually works fairly well overall.

5

Thanks for the awesome information.

I am really curious about MLAT due to the lack of ADS-B compatible aircraft that fly around my area (CYBX). I figured that CYYT would be too far but thought perhaps CYQX could be of help.

I would be willing to install other RPIs around the area but I am curious about the minimum distance. Can the receivers be less than 5 kms away from each other and still work? The largest issue here is access to high speed internet. Several of the villages/areas do not have access to high speed internet.

Thanks again,

Scott.

6

You won’t get much benefit from closely spaced receivers. Ideally you need receivers surrounding the aircraft. It will work to some degree if the aircraft is “outside” the receivers, but not nearly as well. The problem with having a cluster of receivers that are close together is that, for anything other than an aircraft right on top of them, they all see about the same message arrival time, so multilateration doesn’t have much to work with; the differences in timing are so small that measurement errors drown it out.