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MLAT Introduction

Page history last edited by info@coaa.pt 4 years, 1 month ago

Using Multilateration - Mlat


This information was kindly supplied by Tim Plumridge - see this Yahoo group message - many thanks, Tim.


For full details of exactly how Mlat works read the Multilateration tutorial found by doing a search in the Help section of Plane Plotter (PP).  There follows a summary of the basics required in setting it up, which should be read in conjunction with the tutorial.  There are 2 options as to how to use Mlat:-

1.    Become a Ground Station and get Master User Mlat for free.

2.    Obtain a 21 day Mlat trial after which you can pay €12 to continue using it as a Master user.


What does Mlat look like?  See the blue hyperbolae in John Locker's animation here


Accurate PC Time and Station Location are required


Accurate time setting on your PC is required before you are allowed to run Mlat - be sure to install the NTP software.  Your home location is not made available outside the internals of the shared server - the public information is deliberately degraded to about 5km to ensure your privacy.  There is information on accurate time here, and now some notes from John Locker about determining your home location:


To check your location, go to multimap.com.  Put in your exact home address, press the Aerial view button to the top left of the map,  make sure that the circle is on the location of your antenna.  If not double-click on your correct location to put the red circle where it should be.  Look to the bottom right (you may need to scroll the Web browser) and in brackets you'll see your location in decimal degrees - something like Lat: 55:57:04N (55.95115) and Lon: 3:12:09W (-3.20251).  Copy and past those co-ordinates into your PP Home Location box with  N S E or W in front of the figures as appropriate.  For example:  N55.95115  W3.20251 - don't use the other format of the data from MultiMap!  Now press the test function. 


Option 1 - Ground Station - data provider and data user


This option requires you to be able to provide “raw data” on a regular basis (ideally 24/7) but for many users this is simply not possible or practical so as long as data is provided for reasonable amounts of time this is generally OK.  Obviously the more Ground Stations there are up and running the better for the general PP community, especially in areas of limited coverage, as Mlat requires at least 3 Ground Stations (ideally more) to be successful.

To become a Ground Station you need to be running one of the Kinetic SBS-1 (or -1E etc.), The Mode-S Beast, or the microADSB receivers, or use a low-cost R820T/RTL2832U dongle with or without leads (e.g.  one of these from CosyCave) with the dump1090 for Windows software.  The dongle with the dump1090 software (e.g. for the Raspberry Pi) is also available for lower-powered 24 x 7 operation.  Unfortunately the data from RadarBox cannot be processed.  You can also use the PlaneGadget Radar (no longer available).

To get started, then ...


  1. Ensure the PC / laptop clock is accurate and maintained so.  A good (free) program is NTP, and there are easy-to-follow setup instructions here.


  2. If you are using Kinetic BaseStation, upgrade to version 155 or later, as this provides less ambiguity in locations under certain circumstances.  Upgrade to version 161 to remove the need for replacement DLLs.
  3. Ensure the Home location is accurate.  It is not published.  Be sure to use the Test facility on Options, Home location to verify this.  You should get a small street map of the area around your location, with large cross-hairs showing your location.  Note that on Plane Plotter earlier than version 5.5 the cross-hairs may be a little out on displays narrower than 1080 pixels, or less tall than about 810 pixels.  You may ignore this small error, but please upgrade your Plane Plotter when a new version is released.

    Ensure that in BaseStation, Settings, Location Manager, the active location is correctly specified.  This is in decimal degrees, so if you were at Eros, Piccadilly Circus, London, that would be Longitude: -0.134540, Latitude:  51.509851.  Note that longitudes west of Greenwich are specified as negative numbers.  In Plane Plotter you would specify: N51.509851, W0.134540, and here the letters W and E are used to specify West and East of Greenwich.  Plane Plotter will display your location as <degrees> and <decimal minutes>, whereas <decimal-degrees> are used in BaseStation.

    Please be especially careful to specify your location in both Plane Plotter and BaseStation, and change it when you go portable!


  4. For SBS via USB

    i.    Ensure both Base Station and Plane Plotter are both closed.  (Steps ii and iii are no longer required with BaseStation 161)

    iv.    Start Base Station and confirm it is working properly.

    v.     In BaseStation, in the Settings tab, in the Data Settings pop-up dialogue box, under Message Filtering, there is a check box labelled "Ignore Non ADS-B Mode-S Messages".  Ensure this box is not checked.  Later reports suggest that "Process Mode-S Air to Air Replies" must also be checked (from: Roger Tinembart).

    vi.    Open Plane Plotter and under Options, I/O settings ensure the "Raw data for Mlats" box is ticked with 9742 in the UDP/IP local port box.

    vii.    Start to run Plane Plotter


  5. For SBS via Ethernet - please follow Section 3.2 in the Mlat tutorial.
  6. Carry out the Help, Test networking...., Check GS/MU functions.  You may need to configure your router as described below to get this test to pass.
  7. With Plane Plotter and Base Station (for a Ground Station) both up and running, send a message to the group under the header Mlat: asking to be approved as a Ground Station (or Master user). Be sure to quote your two-character share code as well - you can get this from Help, About - it's the two characters after the {registration number}. You can ask in the main Plane Plotter Groups.io group.


  8. Assuming you are approved, the fun starts now with setting up the router!  A good idea is to study the Plane Plotter data Flow PDF file in the PP Groups.io group’s Files section to get an idea of the flow of data for Mlat and how it compares with that for “ordinary” data.  There is such a plethora of different routers, but as a first port of call look in the group’s Files section to see if your specific model is covered.  If not, try www.portforward.com as that gives basic details as to how to forward ports for a wide range of different routers, albeit not specifically for Mlat.


  9. To access your router, and get it to forward the raw data to the appropriate PC / laptop, run a Command prompt and type in IPCONFIG (Accessed either by Start, All programs, Accessories, Command prompt OR Windows button and R simultaneously and then type CMD and Enter.  Amongst the information returned (maybe it needs scrolling up) will be your computer’s IP as well as the router’s IP (sometimes “Default Gateway”), both in the form 192.168.*.*  If at all possible, use a fixed (or static) IP address for your PC, or reserving the IP address for your PC - see the Hints on Port Forwarding below. You can also increase the lease renewal time on your router to, say, a month, should static addresses not be possible.


  10. Type the Router’s IP address in your address bar and Enter; you will then get details on your router.


  11. If you are lucky in that your router’s details are covered in the Files section, great; follow the instructions there.  Otherwise get a clue from www.portforward.com by selecting your model, clicking through the ad on the next page and clicking Default guide near the top of the page.  Generally, look for something similar to Virtual Servers or Application sharing.  (It may need going to an “Advanced settings” option. In any case to access most router’s settings requires a password; by default the Username is usually admin or blank and the password left blank.)  The port number required is 9742 (or range 9742 – 9742), the protocol UDP (not TCP) and the LAN address should be that specific to the PC / laptop as found earlier from IPCONFIG. Finally name it something relevant, and apply or enable the changes.  Sometimes the router loses the assignation to the chosen computer, especially after it doing an upgrade; it can be changed as above.


  12. Not always specifically required, but it MAY help to reboot the router and computer if Mlat doesn’t work.


  13. Depending on the router, other options including Denial of service (DOS) may need to be considered, as well as making adjustments to some firewalls if not using the default Windows one.  At this stage, if Mlat is unsuccessful, a request to the group may get results.


  14. Now is the time to try Mlat! In the Aircraft list, initially look for an entry in green with no positional information (preferably high level), hold control and left click; the Mlat box should appear.


  15. As the cycle continues, the number of raw data reports received should increase until just over 10 seconds when, if successful, the approximate position of your selected aircraft will appear on screen, at which stage an automatic 2nd cycle starts.
  16. You will initially see three lines in the Mlat message box, replaced by five lines at the end of the cycle:

    - the time remaining for this Mlat cycle.  Counts down from 10 seconds.  The (1) (2) etc. are the number of the Mlat cycle.

    - the number of raw reports, which should increase quickly to start with, perhaps less so as the cycle progresses.

    - the hex code for the aircraft of interest.

    - a status report about the success or otherwise of generating the fix.

    - the number of Ground Stations contributing data about this aircraft.

    - the number of Hyper curves generated.

    - the number of users contributing data which could be used to make the hyper curves (by being fortuitously paired with the same data from another user).  The latter are the "Curve users" and that is the number that must be at least 3 for the problem to be soluble.


  17. A contrail can be added to the chosen aircraft as it is Mlat'ed by right clicking it and selecting Contrail.


  18. Mlat will continue on a particular aircraft at intervals after each 10+ second cycle until such time as there are insufficient raw data reports or the user stops the cycle.  To stop it, ensure the top right cross in the Mlat box is red and hit the Esc (Escape) key;  a final positional fix may be given if it had run for long enough before being stopped.  To ensure it does not continue, either Mlat a different aircraft or left click any aircraft in the Aircraft list.


  19. At any time to check the Mlat status, use the Networking Test Functions built into Plane Plotter, or run the PPuser.exe file from the group’s Files section.


  20. Various problems associated with Mlat can be seen in Mlat troubleshooting.
  21. Test your installation, before asking to be added.  Test URL:  http://www.coaa.co.uk/gs-mu-test.php  


Option 2 - Master User - data user only


If for any reason you are unable to meet the criteria of becoming a Ground Station e.g. you are a RadarBox user, don’t have SBS or are simply unable to leave the computer on for long periods of time, then paying is the only option.  Visit http://www.coaa.co.uk/mlat_request.php and continue clicking through to complete the process; this gives a 21 day trial after which you can chose to pay the annual €12 fee if you wish.  Having done this, follow the above from step 6.


Q: My 21 days free Mlat are up and I was looking to see where I can pay the 12 Euros?

A: Visit http://www.coaa.co.uk/mlat_request.php


Q: I've found that page but I cant find anywhere to pay the money, only to request 21 day Mlat again.  Is this the way to go, to re-apply and go through the questionnaire again?

A: Yes - that is why it states on the button you have to click "Request free 21 day Master User free trial or extend Master User Status".


Q: Do I get to enjoy the same facilities if I pay rather than being an Mlat data provider?

A: Yes, you can use Mlat just as an Mlat data provider would.


Once your payment is received and processed, you should automatically become defined as a Master User.  No further action is required.



Using the PlaneGadget Radar


Since Autumn 2010, the PlaneGadget-Radar receiver (no longer available) has also been able to provide data for the Mlat service.  There was a PDF guide (no longer available) on the Plane Gadget Web site.  Version 2.2 or later of the unit is required, and the full version of the Plane Plotter software.



Using 64-bit Windows


Bob Fernandes writes:

I have Windows 7 64bit Ultimate and this is what I did.  (Note that these steps are not required with Base Station or later).


  1. I just reselected Raw Data in I/O Setting for SBS that seem to work
  2. In System32 I changed my FTD2xx.dll to FTD2xx.dll.backup.
  3. In SysWow64 left it as FTD2xx.dll.
  4. In the BaseStation folder I inserted the Vodka substitution DLLs  (there were no FTD2 files to start with in the BaseStation Folder).
  5. Rebooted and all seems to be OK.


Peter Stonebridge writes:

When first loading BaseStation onto the Windows 7, 64 bit machine it wouldn't run because of a "missing .dll".  It was FTD2XX.dll causing the trouble, cannot tell you where I got it, I just did a web search and this site popped up with all sorts of stuff and a free download of FTD2XX.dll.  [Sounds dubious, use only well-known sources - ed.]  Obviously it wasn't quite compatible with Windows 7, 64 bit, although it claimed to be.  Also BaseStation ran fine until I tried to combine Ethernetovich with it and the rest is past history!

This morning I went to www.ftdichip.com and downloaded exactly the same named file and it obviously works fine as I am now an Mlat approved user.



Using Ethernet  with Multi-EM


If you have more details than these, please get in touch so that they can be added to the Wiki.


The settings you need in the Network tab of Multi-EM are:


SBS-1 Ethernet Module

Host (Default Module IP)

Port: 20060


This Multi-EM interface

Host: This is the IP Address of your computer

Port: 20060


Local BaseStation installation points to

Multi EM



Start-up order:

Start Multi-EM first

BaseStation second

Ethernetovitch third

Plane Plotter fourth


Using Mlat with Ethernet


Milan wrote the following in this Yahoo group message.


I also have setup via the Ethernet port.  My SBS is connected via the internet to a location about 5 miles away (on a hill).  On the remote site I have put the SBS-er on the same IP as the local network of that location (  I have then configured the router to port forward Port: 10001 to

Once this is done, you can connect to the SBS via the Internet by going into BaseStation and "Hardware settings" and enter in the PUBLIC IP address of the REMOTE site plus port 10001.  You will need a static IP address go to www.whatismyip.com to find put your IP.  If you don't have a static IP then get one free from http://www.no-ip.com.  If anyone needs settings etc I can allow remote access to my machine via RDP to see the settings for Mlat, Multi-EM, Boris Ethernet etc.  I took me a while to figure it all out also.


Also in this message:  For SBS-1 and PP with MLAT to work you need to install Multi EM, configure it (Radarspotters have a great tutorial) and then run BaseStation, start the Boris Ethernetvoich application and then Plane Plotter.  Your BaseStation hardware settings will point towards the IP address that Multi EM is on and port 20060 (usually).


Setting up my router


If you have a common model of router you may be able to find information about setting up the box in the Plane Plotter Groups.io Files Area.  If not, read on about port forwarding...


Once you have your router set correctly, do remember to backup your router settings!  See you router instructions for how to do this, as it will be different on various routers.


There is information on some specific routers here.


Hint on Port Forwarding


You may find the information here helpful about port forwarding.  In particular, for any given router you can start at the URL below, and then follow the steps for your particular router.




  1. select your router
  2. skip the advert (click top right)
  3. follow the instructions, but where the port number is given as 41170, substitute port 9742 instead


If you get a lot of Mlat packets coming into your PC it is possible that the router will think your PC is under attack, and the router may close the path, resulting in very few Mlat responses and hence no Mlat positions.  In that case, you will need to dig out your router manual and disable the D.o.S. (Denial of Service) function.  Some PC security software may also need configuring to disable the D.o.S. function.  As Plane Plotter will be getting apparently unsolicited packets from the Internet, your Windows firewall software may need to be set to allow this - for example: "Enable Incoming" in the Windows firewall, or "Act as a server" in Zone Alarm.


Rather than relying on the IP address which your router automatically assigns to your PC using DHCP, consider moving to fixed computer IPs - a static IP address, or using the Address Reservation feature of your router to tie a particular IP address to the MAC (Hardware) address of your PC - see here.  How to find the MAC address of your PC's network card - see here.  For some more information - see: http://portforward.com/networking/staticip.htm  This will prevent the confusing and frustrating problem of Mlat working one day but not the next.


"Marijn 'The Guide' de Gids" writes:


Router Port Forwarding can be realised by using UPNP.  Plane Plotter makes a batch file upnpmaster.bat in the Plane Plotter directory.

   * Router must support UPNP (and have it enabled)
   * Run upnpmaster.bat

I know UPNP is also a possible security hole but most 'home'  routers have it enabled.  I use it over here because I have DHCP enabled on my 'SBS server' and unfortunately it's not possible to reserve DHCP addresses in the router.


Is there a tutorial about all this - a video showing me how?


Yes!  Nic Storey has created another in his popular video series entitled: Ground Station Setup


What receiver should I use?


The Beast and SBS receivers have two important advantages over anything based on a dongle.  Firstly the receiver is specifically designed for 1090 MHz with appropriate filtering etc. so outperforms any dongle based receiver.  Secondly the decoding of the Mode-S data stream is done in dedicated hardware/firmware whereas all of the dongle-based solutions rely on the PC to perform the demodulation and decoding.  The result is that the message rate on the dedicated receivers massively exceeds the message rate from a dongle-based solution.  For normal use, especially where range is not an issue, this may not be significant, but for multilateration, you will remember from the tutorial that you studied, that it relies on timing pairs of messages (one with position and one unknown) received at two Ground Stations.  If a dongle based solution is only delivering a fraction of the incoming messages, then the chances of such coincidences occurring is dramatically reduced so the success rate for Mlats is much lower if the Ground Station are dongle-based.  In addition to this, the raw data time tags from the SBS1 are at 20MHz and from the Beast are at 12MHz.  Those from dongle-based solutions are only at 2MHz which corresponds to a spatial resolution of 150 metres but the geometry of the hyperbolae is such that this can introduce an error in aircraft position of ten times that value so in general fixes based on dongle-receivers are much less accurate.

Of course, the low capital cost and the low running costs of an Raspberry Pi dongle-based Ground Station means that many more such Ground Station can be deployed, which might make up for the reduced performance and in any case "half a loaf is better than no bread".  However, we would always urge those who are able to operate a Ground Station based on a dedicated receiver, not to switch to a dongle-based receiver unless it is imperative.
(Information from Bev's Yahoo post - URL: https://groups.yahoo.com/neo/groups/planeplotter/conversations/messages/130921)

A recent receiver which is a similar size to the RTL-dongle and can work with both the Raspberry Pi and Windows computers is the Airspy Mini.  Because of its higher sampling rate if provides much more accurate Mlat data.  It costs just over £/$/€ 100.  The larger Airspy is also suitable.  See: https://groups.yahoo.com/neo/groups/planeplotter/conversations/messages/131152


Problems with Mlat?


Check out the Mlat Troubleshooting Guide

There is a self-help group you can join for Mlat setup here:  https://groups.io/g/planeplotter/



Recent Mlat advances


Shared Mlat


- announcement of version http://groups.yahoo.com/group/planeplotter/message/28866

- chart requirements: http://groups.yahoo.com/group/planeplotter/message/29459


Auto Mlat


Assuming that you are a Master User, then checking the Auto Mlat option in Options, I/O settings means that whenever Plane Plotter is idle (no user interaction for some time), every minute or so it will attempt to Mlat any position-less aircraft in the list that have sufficient Ground Stations in the sharer list.  Unlike manual Mlats, the progress is shown in the status bar and not in a pop up progress window.


Why can't it be easier to set up as a Ground Station and Master User?


See: PC networking for Mlat


How are different message types used in Mlat?


See: Message Types

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