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Looking for ideas to help identify traffic over a gliderport

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  • Looking for ideas to help identify traffic over a gliderport

    Hello, this is my first post here, so I apologize if this has been asked and answered before (but I doubt it...?)

    I'm the safety officer for a soaring club in Canada. ADS-B is not yet mandated here. We've recently, post-Covid, been seeing an order-of-magnitude increase in the amount of both overhead jetliners, and of training flights from nearby schools, coming too close for comfort to our pattern. We're looking for ways to help identify that traffic.

    One way to identify that traffic is an ADS-B ground station. But while this would undoubtedly help identify the overhead jetliners, it would not help us identify training/survey/ag spray flights - they're generally not ADS-B equipped. So, in addition to ADS-B, I'd like to come up with a way to pick up transponders. Our club is theoretically within range of the nearest international airport's secondary radar, even on the ground - which again, is great for overhead commercial traffic, but not low altitude single piston training flights.

    For low altitude flights, I think we'll need a transmitter - so we can ping, instead of just receiving the pongs. I'm only interested in traffic in the immediate vicinity, say 10 miles or so. The rest, we can rely on ADS-B or transponders for. We're on very flat land (great farmland), 35nm from the nearest international airport, and on 1000' higher ground.

    So what would be people's recommendations for setting something up, both ADS-B and classic transponder based, that could identify overhead traffic? We have the necessary antenna masts and probably the budget for something semi-professional, if I can gather the collective will to do it.

    My apologies for any niavete. I'm a licensed recreational pilot but the details and physics of flight tracking are largely left to professionals.

    (I can respond via PM with precise geographical details)

  • #2
    Adsb as a whole includes modeS with no gps integration when a receiver is used.

    You get to see standard transponders or replies to ground interrogation. But no positions. Just altitude.

    Not limited to full adsb.

    So before military was equipped in some areas, you still could 'see'. Just not where.
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers


    • #3
      If you had an RPi based ground station running PiAware (RPi OS and Mode-S data decoding) there's a high possibility that aircraft with Mode-S but not ADS-B can be tracked using MLAT. PiAware displays all MLAT tracked aircraft whereas many of the public tracking websites/apps do not.

      Google "PiAware". The service is from a FlightRadar24 US based competitor so I'll not post a link here.

      Radarspotting since 2005


      • #4
        Pinging like a radar is out of the question for you unless you can get nav canada to set a radar up for you or share their data. (i suppose it wouldn't hurt to approach them.)
        It's punishable quite severly in most places to send on frequencies involved with ATC. Don't do that.

        For MLAT you would need to set up 4 pretty inexpensive receivers ($100 to $300 each depending if you buy components or a preassembled unit).
        They should be in a square with about 1 mile between the receivers, optimally seeing the horizon in all directions.

        Software wise i'd recommend this, you can contribute to (and get back MLAT results back from) multiple services:
        FR24 will not return MLAT results ever. It also has a new policy to disable MLAT anyway if you feed other aggregators which seems weird.
        Note that ModeC transponders are not covered by the available MLAT networks, only ModeS transponders.


        • #5
          Short reply
          If an aircraft is NOT fitted with a transmitter/transponder broadcasting a signal regularly, it cannot be detected by any piece of equipment on ground, except a conventional RADAR.

          Possessing/operating a conventional RADAR to detect flying objects (except for armed forces & civil aviation) is illegal in most countries.






          • #6
            abcd567 - Going off course here, but that is exactly a feature Planeplotter uses/has. It uses 'Beamfinder' (and the knowing rotational speed of the radar) with a capable receiver (beast/radarcape) reads the interrogation replies and works out positional data between other clients like MLAT does. So not only conventional radar
            Posts not to be taken as official support representation - Just a helpful uploader who tinkers


            • #7
              What if the aircraft is NOT fitted with equipment to reply to interrogations, like all aircraft used to be 30 years ago?

              The conventional RADAR does NOT depend on equipment in the aircraft. It transmitts short bursts of RF signal. There is no responce transmitted by the aircrsft being detected. The conventional Radar detects its own bursts of signal after it is reflected by aircraft body, and calculates position based on direction & time lag of reflected signal.

              In those days interrogation was done on HF by a system known as SELCALL. The airport will transmit a coded signal on HF which had id for the aircraft for which the selcall is being issued. All aicraft in the area will receive it, but as the transmitted id does not match with their id, it will be ignored by all except the aircrsft with whose id the transmitted id matches. The responce of that aircraft will not be a reply data signal. The pilot of that specific aircraft will respond on voice transmission by saying "selcall checked ok".


              • #8
                I'm somewhat well versed on how radar works. We're not considering a primary radar, as yes, it would be illegal, and prohibitively expensive.

                What I'm trying to work out is whether or not it's possible:

                A) To pick up transponder "pongs" - replies to transponder interrogations sent either by other aircraft's TCAS, or from nearby radar sites' pings.
                B) Where aircraft are too low to receive an ATC ping, whether or not there is some way we could send interrogations. It's looking more and more like this is not possible.

                While commercial traffic will almost certainly be ADS-B / Mode S equipped, most of the general aviation aircraft here are limited to mode C, so I'm not sure what we could expect to figure out or whether it's worth the effort involved.

                It's also possible, as we operate an airfield, that we could be granted a license to use a limited range secondary radar, something small and omnidirectional with a limited range, to generate transponder replies from nearby aircraft. It's not likely, but it's not impossible.

                Another idea is leaving the transponder in one of our tow planes on. I'm not sure though how useful that would be. Again, it would likely help with commercial traffic, but probably not be of any use with any aircraft lacking a collision avoidance system.

                One other thought is, if anyone here is aware of the ins and outs of FLARM, and how it functions, anything you could provide would be useful. All I know is that it actively looks for other FLARM units, and can detect altitude, heading and bearing from mode C transponders. Whether or not it can also precipitate a transponder response on 1090Mhz, or simply relies on responses sent by other stations, is something I don't know.


                • #9
                  Interrogations are just as illegal as primary radar, possibly more so as you could do primary radar with a frequency that aren't on frequencie used by aircraft.
                  (but power levels that are useful would probably be illegal as well)

                  You don't necessarily need interrogations to get ModeS squitter, that should be enough for MLAT, i think they (even without interrogation send the altitude every second as well).

                  Tracking ModeC you're looking at rewriting the server and client portion of mlat-server and running it yourself with 4 or more stations.
                  It's quite a bit of work. I have modified the software i should know.

                  For FLARM you'd have to get yet another receiver and there is only a very bad open source solution to integrate with the MLAT / ADS-B data for display. It's ugly but i'd call it possible.
                  Google OGN? They should have info on FLARM.

                  Why don't you start with a single ADS-B receiver and see what you can pick up.
                  Maybe FA or adsbexchange already have a station or two in your area.
                  Last edited by wiedehopf; 2022-09-14, 03:29.


                  • #10
                    We'll be starting with a single ADS-B receiver for sure - we already have most of the required hardware. With any luck it will already provide everything we need. Mode C could be an issue if we want positional data, as putting in 4 stations is problematic simply because it would be difficult to supply power to them. I was unaware that Mode S actively broadcasts, so that should be helpful for us.

                    It's the small GA aircraft that will be the most problematic to identify. We can't identify all of them anyway, as some of them around us have no radios at all, let alone transponders.

                    As for whether or not FA or adsbexhange have a station in our area, I haven't found one yet, but is there a list somewhere of those ground stations?