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Is VDL-4 in use alongside ADS-B? Is it possible to build kit to decode it?

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  • Is VDL-4 in use alongside ADS-B? Is it possible to build kit to decode it?


    I am new to this subject and would like to build my own receiving equipment for monitoring automatic transmissions of the ADS-B kind. I have no experience of building stuff that works at microwave frequencies, even the bottom end such as 1090MHZ, and short of using a suitable sat TV module and cobbling the tuning of it together, I doubt I could do it well. However, in the past, I have built a number of receivers operating at VHF frequencies.

    I have been reading around the subject on the net, and seem to think that there is a parallel VHF system besides ADS-B has also been mandated for civil aircraft, and it looks like it might cover the same kind of data. If this is true, I think I would have a lot better chance of building a receiver to work on the VHF airband frequencies, since I built an FM WEFAX satellite receiver about twenty years back which worked very well.

    So, my questions are:

    Is VDL-4 being used alongside ADS-B?

    Does it send the same data as ADS-B?

    What frequencies are used for VDL-4? I'll probably make a crystal controlled L/O for the project.

    I envisage that the main problem might be in having to programme the microprocessor myself to decode the data. I know that chips are already available pre-programmed to decode ADS-B, but the data rates of ADS-B and VDL-4 are very different, which probably means the chip would need different programming. This would be a deal breaker for me, I suspect, as that is not my game.

    Many thanks for any help any of you experts might be able to share here.

    Perhaps I am barking up the wrong tree with this idea, in which case feel free to disabuse me of the half baked plan.

  • #2
    I know absolutely nothing about VDL-4 but if this Meetings Calendar at Eurocontrol offers any insight, don't hold your breath

    Radarspotting since 2005


    • #3
      Thanks Anmer. I found numerous intentions to mandate VDL-4, and co channel interference tests, but most of what I found was from around 2000 - 2005. I just wondered if it had ever got 'off the ground', pun intended....

      If there was some easy home brew way of getting the same data that ADS-B provides, I might be up for trying it. I haven't done any home brew stuff for years and just felt I'd be more at home with lower frequencies. On the other hand, some people (including RadarGadgets) have done some lovely stuff with adapted sat TV tuners. Maybe that is the best way to go, but it is difficult to know which ones work and which don't. Also, I'd need a scope to line up the local oscillator, I expect, even if I knew which pin to vary the voltage on. Another problem in messing about with surplus tv tuner units is getting any data sheet for them.


      I found a very useful link here :

      The really detailed stuff is in a zip file of pdfs at the end of that link. I'm just trying to take it all in.
      Last edited by evilV; 2010-04-27, 19:05. Reason: found additional information and added it.


      • #4
        You can find all you need to know about VDL-4 on this website: I think there's enough to put you off building anything to do with VDL-4, which requires a TDMA structure and timebase generators for UTC. In essence, it's going to work across existing VHF airband frequencies, still to be designated, and will carry multiplexed air-to- ground atc exchanges on what are presently highly congested analogue amplitude modulated frequencies!

        I think VDL-4 lost its way a little when the industry moved to 8.33 kHz frequency stepping some years ago, which increased the potential of exisiting airband voice channels from 720 to in excess of 2,000! Good luck with your project!


        • #5
          Thanks Duncan. I wrote that post a couple of weeks ago and since then I realised it was a non-starter. LOL. I was only trying to avoid building a S mount kit, and thought a simple VHF old style crystal controlled receiver would be easier (I've made them before). Once I found out some of what it was about, I realised it would be a most counter productive move.

          Thanks for your advice.