FlightAware Discussions

Mlat sync

On my stats page it shows that my mlat is synced with around 350 nearby receivers.

I know ADSBEXCHANGE.COM has a web page listing somewhere that lists something to do with mlat synchronisation so am curious, I thought mlat just needed 3 or 4 stations to position so what is the benefit of syncing with so many?

Plus, I’m guessing that the 350 with which I am synced cant all be close by so how far away might these other stations be?

Geoff

This is reporting receivers that you have clock synchronization with. Synchronizing the clocks is the first step and is necessary before any actual multilateration can be done, and it’s not predictable which receivers will actually see copies of a particular message that needs multilateration, so it makes sense to do it with as many nearby receivers as possible ahead of time.

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What is the effective maximum distance two receiverscan be separated and still synchronise?

Thanks,

S

Several hundred NM. The requirement is that both receivers can see the same ADS-B-transmitting aircraft.

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How does it determine which devices to sync with?

Geoff

The server “knows” your reported location… and, like Obj said above, if the timings are correct… you have a match.

MLAT is less and less important. The number of MLAT flights already dropped a lot in US, and it’s not even 2020. I think it’s the same in EU and Australia.

Most general aviation aircraft don’t have ADS-B in Europe, and UAT doesn’t exist here at the moment. I’m still seeing 5-600 mlat aircraft a day, with a further 500 or so mode-s only aircraft here. That’s with syncing 700 stations, so mlat will be relevant for some time here I think.

All receivers in the same mlat region (i.e. handled by the same server instance) try to sync with each other. This can be a few thousand receivers. The receivers aren’t involved in the decision, they just get told what traffic to forward.

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When I started this hobby in summer of 2017, in US, the MLAT traffic was approximate 1/3 of total traffic.
Now is less than 1/10; yesterday I had 2800 ADS-B planes and 240 MLAT.

I think ads-b was less common in the US initially though so there will be a more noticeable change there. I haven’t noticed a big increase in the number of ads-b aircraft compared to mode-s only here, but I don’t have data going back to compare it for sure. There is also a mandate for larger aircraft to have ads-b installed by June next year here, so it will be interesting to see what changes between now and then.

I’m also curious to see if there will be an increase in the number of mlat positions I get when I move my antenna to the roof later this week. From plots I made of mlat results, there are significant gaps in coverage at the moment.

Here even the trainer planes have ADS-B now, I am watching them on ADS-B versus UAT, and they are not there.