FlightAware Discussions

Max Number of Syncd Nearby Receivers

What’s the maximum number stations that can be synced? I’m up to 23…

“Multilateration (MLAT): Supported / Enabled (synchronized with 23 nearby receivers)”


Receiver # 1 (Cantenna+Generic DVB-T black+ RPi B+):
Multilateration (MLAT): Supported / Enabled (synchronized with 48 nearby receivers)

Receiver # 2 (FA 26" Antenna+FA Filter+ProStick+RPi 2):
Multilateration (MLAT): Supported / Enabled (synchronized with 63 nearby receivers)

Receiver # 3 (Cantenna+FA Filter+ProStick+Orange Pi PC):
Multilateration (MLAT): Supported / Enabled (synchronized with 63 nearby receivers)

Synched with 176 and 164 nearby receivers – Silicon Valley is a target-rich environment…

bob k6rtm

About 120 in NYC.

For flightaware.com/adsb/stats/user/ … tats-24223 I get

Feeder Type: PiAware (Debian Package Add-on) 3.2.0~dev
Multilateration (MLAT): Supported / Enabled (synchronized with 118 nearby receivers)

Yikes…my concerns are abated. I was thinking more synced units would cause my PI to bog down. Disregard!


Sort of along these lines - is there anything we can do to extend the distance “Nearby ADS-B sites” cuts off at? My synced with sites regularly exceed the number of sites in the nearby ADSB sites list, and judging by my range chart I overlap sites which don’t appear in the nearby sites list by quite a margin.

I think the number is going to be a result of how many messages your station is hearing in common with surrounding stations. I suspect two variables influence this, 1) the density of stations in your area and 2) the performance of “how much” your station is hearing that others are also hearing. Have you maximized your height, or position (to minimize obstructions on the horizon)?

edit: precision of time synchronization also tends to affect this… tuning your ntp settings might slightly skew the numbers, too.

NTP has nothing to do with it. Using a STD dongle, the timing is based on an internal unique clock(within the dongle) and timing messages from aircraft.
Some receivers, like the radarcape, embed a GPS time stamp into the message. It needs to be done in the receiver hardware itself as USB has too much timing variation and cannot be considered reliable. USB is a shared bus.

Is there a simple (understandable by non technical person (me)) reason why the number of stations synched varies?

I go from a high of 23 or so down to 7. Haven’t notice anything regular or a pattern.

It seems to me it’s highly dependent on traffic. If you have traffic to the north, south, west, and east, you will likely sync with receivers to the north, south, east, and west. If you have traffic only to the north, those receivers to the south will likely drop off.

It would be really cool if we could see the locations of receivers we’ve synced with on a map and be able to watch them blink on/off as they are synced. I suspect the correlation with traffic will be obvious with such a visualization.

Good question. I suspect this comes down to an arbitrary definition of “nearby”. Just speculating here, but I suspect “nearby” means within radio range of your receiver, which is fine for aircraft, but too close for synced stations. It doesn’t take much thought to realize the distance for two sites to sync could be double this distance, the commonly viewed aircraft being at the edge of reception distance for each receiver and between the receivers.

Actually, I always thought the list of nearby ADS-B sites was just a listing of the closest sits that fit into the table (closest X receivers). How many receivers are people seeing in their list? I’m seeing 25, including my own two. Same 25 whether I’m viewing one receiver or the other.

I noticed that the site disabled MLAT since “no reliable time source”.
I enabled NTP and since then I see more MLAT overall. I am not sure if this is the root cause but the message about unreliable time source is gone forever.
Your presumption that the receivers sync only if there is an airplane being tracked is confirmed also by me.

Multilateration (MLAT): Supported / Enabled (synchronized with 825 nearby receivers)


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When we turned on the piaware receiver at Cocos Keeling island in the middle of the Indian Ocean the nearest inhabitation was Christmas island about 1000km away and they had no flightaware receiver.

Consequently, there were precisely zero nearby receivers.

interestingly, on a good day your brilliant site records a couple of thousand aircraft that are also reported by possibly hundreds of other sides.

On a really good day the Cocos Keeling site may see 10 aircraft but no-one else reports them for several hours in any direction.


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And that’s what makes the Cocos Keeling feeder more important than mine. If mine went off, nobody would blink but if that one went off, it would leave a hole. It’s not all about figures.

I was very pleased to make contact with VK9CZ on Cocos Keeling on 15m CW and USB and 10m USB back in April 2013.


Multilateration (MLAT): Supported / Enabled (synchronized with 841 nearby receivers)


I just saw this and was curious.

I’m seeing 965 right now. I’m about 40 miles from London Heathrow.

Is there any upper limit to the number of nearby receivers you can sync with?

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Oh Andy…

Screenshot 2020-07-06 at 19.01.33

:smiley: :smiley: :smiley:

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1000-ish, probably. It’s limited by the number of receivers in the same mlat region, and the regions are sized so that they’re not handling too many receivers each, which in practice means somewhere around 1000-ish.

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Like it Keith!

Looks like you are slightly higher up the UK rankings than me too! Well done :wink:

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