MLAT

[Angelus1971]

Hi

Not sure where to post this as its not specific to FR24 software but to the users in the North-east of Scotland who feed MLAT into the network (please feel free to send me to the correct location / forum to get this request out to the most users - I'm sure its not just my area that is having these problems!)

People, can you PLEASE check your position reported from your MLAT equipment. For maybe the last 2 - 3 weeks now, and I don't know if its a new user or not or whether is deliberate or not, but the MLAT data being reported to ALL the feeding software has been diabolical. The data trails of the MLAT aircraft has been all over the place. The general area is correct as I'm sure the software is trying to average out the wrong reports but it is getting to the stage now that's its unusable. If the aircraft flew the way their plots show, the pilots would be arrested for drunk flying. It never used to be this way, but like I said, its getting worse and worse.

Could you please check your feeds and mention to your friends and other feeders you may know to get their MLAT equipment checked and sorted out.

Thanks.

[Oblivian]

Theres nothing to sort?

It only sends, the client users don't receive anything. As long as the GPS coords are correct when registered, and enough of them are in contact with the same aircraft, it will be smooth. If it is only occasional contact (or few at once) it can't plot correctly

But there is meant to be features in place to correct/ignore feeders if above thresholds

And its probably about 80% of feeders never check forums

[delcomp]

Four F- Recievers Recieving the same aircraft,.. At the same time,. For MLAT working

Im not sure if the New FR24 version,. If other (T- N-) are now inculded..

The F- Recieves have GPS,.And therefore make MLAT possible.

[Angelus1971]

I know Oblivion, I live in hope that the offender reads the forums or somebody mentions it and they get to hear about it. Its definitely their GPS co-ords that's off and it is a new feeder to the region (unless an current feeder has re-setup incorrectly).

delcomp - i'm not sure whose network the feeder is on but its affecting all of the ones I'm in (its not me, I doubled checked before writing the first post).

[Oblivian]

The radar source will give a hint despite it being MLAT. FR ones vs RPi are numbered differently (and FR always preferred over Pi)

[Kpin]

I know Oblivion, I live in hope that the offender reads the forums or somebody mentions it and they get to hear about it. Its definitely their GPS co-ords that's off and it is a new feeder to the region (unless an current feeder has re-setup incorrectly).

delcomp - i'm not sure whose network the feeder is on but its affecting all of the ones I'm in (its not me, I doubled checked before writing the first post).

What do you mean by 'network'?
The individual feeders are not involved in calculations - that is done server side. And the GPS is not use for positioning - only for timing. And only GPS time of F-feeders are used

More likely than some faulty feeder coming online is that mayby a feeder has gone offline, thereby degrading MLAT. Or drunk pilots :-)

[Sam26K]

i'm still confused about MLAT. So is a minimum requirement for MLAT is that the receiver has a local GPS receiver so that it has a real time GPS time stamp?

If that's the limitation then it should be easy to do that with RPi's too.

[Oblivian]

MLAT requires 4+ receivers.
- FR24 Receiver produced MLAT prioritised for accuracy
- Various combinations of receivers can contribute with GPS/time tagged receivers
- at least 1x FR24 receiver needed in combination
- All need to have contact with the same Mode-S Only aircraft (and 1x ADSB reference aircraft).

Attributed on the map caclulated from FR24 boxes as:
T-MLAT (Europe/Africa)
T-MLAT2 (North and South America)
T-MLAT5 (Asia/India/Japan)
T-MLAT3 (Oceania)

Attributed on the map calculated from RPi feeders:
T-MLAT6/7

MLAT from RPis is used. GPS is required on a F- receiver for time. NTP is on Pi as they are only used as a reference point. So the location entered in GPS has to be accurate.

The server aligns all the data focused on the F- box. Hence 90% of the time you don't see the normal MLAT6/7 flag.

There are posts from both developers outlaying this. Noting GPS is not required on Pis, not going to help. As long as the back end is enabled, the data from it us used for reference

[Oblivian]

Olov stating it is back, but will be secondary

http://forum.flightradar24.com/threads/9132-Beta-test-new-Flightradar24-MLAT-software-for-Raspberry-Pi?p=76188&viewfull=1#post76188

Replying to you, enforcing a GPS unit won't help a Pi

http://forum.flightradar24.com/threads/9132-Beta-test-new-Flightradar24-MLAT-software-for-Raspberry-Pi?p=76233&viewfull=1#post76233

[Sam26K]

Oh yes, now I remember. The GPS receiver has to be integrated into the receiver. Thanks for reminding my Oblivian.
Now how do we do that economically?.

[hnapel]

Nevertheless I added a PPS signal to my PI from an external GPS based time server, so at least my clock is very accurate, hope it helps, even as a reference source.

[Sam26K]

As I understand the limitation with MLAT and RPi is that the ADS-B mode S receiver has to have the GPS receiver actually integrated into the ADS-B mode S receiver. A separate mode-S receiver (eg typical USB stick) and GPS receiver plugged into an RPi doesn't work yet anyway.

To those in the know feel free to correct me if that is wrong.