Unstable MLAT synch

[vanosg]

Hi everyone- I recently moved my PiAware setup to a new location- unfortunately, it is in a slightly wooded area, so I get only about a 50 mile radius (open to thoughts on improving that as well, but that’s not the reason for the post). Looking at the logs, I noticed the receiver is having issues maintaining synchronization for MLAT. For example:

Sep 13 17:51:04 flightaware piaware[395]: mlat-client(468): Server status:   synchronized with 249 nearby receivers
Sep 13 17:51:04 flightaware piaware[395]: mlat-client(468): Receiver:   16.5 msg/s received        6.5 msg/s processed (39%)
Sep 13 17:51:04 flightaware piaware[395]: mlat-client(468): Server:      0.0 kB/s from server    0.0kB/s TCP to server     0.1kB/s UDP to server
Sep 13 17:51:04 flightaware piaware[395]: mlat-client(468): Results:  2.0 positions/minute
Sep 13 17:51:04 flightaware piaware[395]: mlat-client(468): Aircraft: 4 of 4 Mode S, 2 of 2 ADS-B used
Sep 13 17:55:54 flightaware piaware[395]: 19743 msgs recv'd from dump1090-fa (128 in last 5m); 19743 msgs sent to FlightAware
Sep 13 18:00:54 flightaware piaware[395]: 19861 msgs recv'd from dump1090-fa (118 in last 5m); 19861 msgs sent to FlightAware
Sep 13 18:05:54 flightaware piaware[395]: 20003 msgs recv'd from dump1090-fa (142 in last 5m); 20003 msgs sent to FlightAware
Sep 13 18:06:04 flightaware piaware[395]: mlat-client(468): Receiver status: connected
Sep 13 18:06:04 flightaware piaware[395]: mlat-client(468): Server status:   synchronized with 197 nearby receivers
Sep 13 18:06:04 flightaware piaware[395]: mlat-client(468): Receiver:   15.0 msg/s received        5.4 msg/s processed (36%)
Sep 13 18:06:04 flightaware piaware[395]: mlat-client(468): Server:      0.0 kB/s from server    0.0kB/s TCP to server     0.1kB/s UDP to server
Sep 13 18:06:05 flightaware piaware[395]: mlat-client(468): Results:  1.0 positions/minute
Sep 13 18:06:05 flightaware piaware[395]: mlat-client(468): Aircraft: 6 of 6 Mode S, 2 of 2 ADS-B used
Sep 13 18:10:54 flightaware piaware[395]: 20185 msgs recv'd from dump1090-fa (182 in last 5m); 20185 msgs sent to FlightAware
Sep 13 18:15:54 flightaware piaware[395]: 20250 msgs recv'd from dump1090-fa (65 in last 5m); 20250 msgs sent to FlightAware
Sep 13 18:20:54 flightaware piaware[395]: 20331 msgs recv'd from dump1090-fa (81 in last 5m); 20331 msgs sent to FlightAware
Sep 13 18:21:05 flightaware piaware[395]: mlat-client(468): Receiver status: connected
Sep 13 18:21:05 flightaware piaware[395]: mlat-client(468): Server status:   not synchronized with any nearby receivers
Sep 13 18:21:05 flightaware piaware[395]: mlat-client(468): Receiver:   12.1 msg/s received        4.6 msg/s processed (38%)
Sep 13 18:21:05 flightaware piaware[395]: mlat-client(468): Server:      0.0 kB/s from server    0.0kB/s TCP to server     0.0kB/s UDP to server
Sep 13 18:21:05 flightaware piaware[395]: mlat-client(468): Results:  2.7 positions/minute
Sep 13 18:21:05 flightaware piaware[395]: mlat-client(468): Aircraft: 3 of 3 Mode S, 3 of 3 ADS-B used
Sep 13 18:25:54 flightaware piaware[395]: 20506 msgs recv'd from dump1090-fa (175 in last 5m); 20506 msgs sent to FlightAware
Sep 13 18:30:54 flightaware piaware[395]: 20625 msgs recv'd from dump1090-fa (119 in last 5m); 20625 msgs sent to FlightAware
Sep 13 18:35:54 flightaware piaware[395]: 20683 msgs recv'd from dump1090-fa (58 in last 5m); 20683 msgs sent to FlightAware
Sep 13 18:36:05 flightaware piaware[395]: mlat-client(468): Receiver status: connected
Sep 13 18:36:05 flightaware piaware[395]: mlat-client(468): Server status:   synchronized with 8 nearby receivers
Sep 13 18:36:05 flightaware piaware[395]: mlat-client(468): Receiver:   11.7 msg/s received        4.7 msg/s processed (40%)
Sep 13 18:36:05 flightaware piaware[395]: mlat-client(468): Server:      0.0 kB/s from server    0.0kB/s TCP to server     0.1kB/s UDP to server
Sep 13 18:36:05 flightaware piaware[395]: mlat-client(468): Results:  2.9 positions/minute
Sep 13 18:36:05 flightaware piaware[395]: mlat-client(468): Aircraft: 2 of 2 Mode S, 1 of 1 ADS-B used
Sep 13 18:40:54 flightaware piaware[395]: 20767 msgs recv'd from dump1090-fa (84 in last 5m); 20767 msgs sent to FlightAware
Sep 13 18:45:54 flightaware piaware[395]: 20865 msgs recv'd from dump1090-fa (98 in last 5m); 20865 msgs sent to FlightAware
Sep 13 18:50:54 flightaware piaware[395]: 20907 msgs recv'd from dump1090-fa (42 in last 5m); 20907 msgs sent to FlightAware
Sep 13 18:51:06 flightaware piaware[395]: mlat-client(468): Receiver status: connected
Sep 13 18:51:06 flightaware piaware[395]: mlat-client(468): Server status:   not synchronized with any nearby receivers
Sep 13 18:51:06 flightaware piaware[395]: mlat-client(468): Receiver:    7.8 msg/s received        3.0 msg/s processed (39%)
Sep 13 18:51:06 flightaware piaware[395]: mlat-client(468): Server:      0.0 kB/s from server    0.0kB/s TCP to server     0.0kB/s UDP to server
Sep 13 18:51:06 flightaware piaware[395]: mlat-client(468): Results:  1.5 positions/minute
Sep 13 18:51:06 flightaware piaware[395]: mlat-client(468): Aircraft: 5 of 5 Mode S, 1 of 1 ADS-B used

It can go for hours at a time without being synchronized, but you can see here how it falls in and out of synch. While not that many, and maybe not related, I did also find a few

Sep 13 20:21:08 flightaware piaware[395]: mlat-client(468): Out-of-order timestamps: 1

lines as well, but they are in no way prevalent (somewhere around 5 instances a day), but I’m including that just in case there could be a relation. One last piece of info, I’ve run the gain at 12, 22db and 49db just to see if that affected anything, but it all seems pretty consistent across those values.

Is the MLAT desynch normal? Maybe I’m not seeing enough beacons with the limited line of sight? Any thoughts you can provide on that matter (or thoughts on how to boost reception in a forest ) would be much appreciated, thank you!

[obj]

Low message rate and few ADS-B equipped aircraft. I suspect it is just that you often don’t see enough ADS-B messages to keep synchronization.

The “not synchronized” line is a snapshot of the current state, it’s possible that you are regularly gaining/losing sync in between log messages.

[wiedehopf]

@vanosg

I recently moved my PiAware setup to a new location- unfortunately, it is in a slightly wooded area, so I get only about a 50 mile radius (open to thoughts on improving that as well, but that’s not the reason for the post). Looking at the logs, I noticed the receiver is having issues maintaining synchronization for MLAT.

Actually improving reception will likely improve MLAT sync in your case (because you’re currently seeing so few ADS-B aircraft which are required for sync).
Provided the location is configured precisely and there are no power issues leading to jumping timestamps.

Hard to tell what your issue is.
Trees usually don’t restrict reception quite as much as in your case, that would need some massive amount of trees.
You should describe your setup in detail if you want suggestions in regards to that.

[SoNic67]

@vanosg

Is the MLAT desynch normal? Maybe I’m not seeing enough beacons with the limited line of sight?

Besides that small range that definitely can be an issue, I see that you are in MD US. The MLAT in US dropped drastically this year, due to FCC mandate for ADS-B.
I am in VA, my MLAT is synchronized with 170 receivers, and I see only about 1000-2000 MLAT positions out of 130k-140k per day. Or 20 MLAT aircraft from a total of 1400-1500.

[vanosg]

I got 70 MLAT positions 2 days ago, and only 4 yesterday

Thanks to all for these super helpful responses. It’ll be interesting to see if the my max detection radius changes once the leaves drop, and if the MLAT hits subsequently pick up.

[jonhawkes2030]

I am in NYC and only get a few thousand a day. I am sure this was tens of thousands last year.

[markrrichardson]

My MLAT is highly variable around Northeast Ohio. 0.2% to 1.5% of my total positions. Only have data for 2020…wish i had last year for a fair comparison.