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Which is more important: Hardware, sightlines or elevation?

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  • Which is more important: Hardware, sightlines or elevation?

    Hi.

    My stock-standard FR24 ADS-B rig is at ~1,830m ASL on a mountain range (-44.414, 170.01) and I'm detecting and losing aircraft at ranges between 500-600 km.

    I'll soon be moving the setup to the highest peak, ~1,900m ASL: Not only is it 70m higher than the current site, it has unobstructed 360 degree horizon views down to 0-1 degrees alt., unlike the current site, which loses up to 6 degrees alt. in a couple of directions.

    There is essentially zero noise at this site -- I'm the only thing up here, and there's 2/3rds of nothing in most directions for scores of kms -- so is any hardware change likely to further increase the range?

    Cheers, BPO.
    Last edited by BPO; 2014-03-22, 03:22.

  • #2
    It will be interesting to see if FR24 remove the 400km limit from your stations submissions that they have in place for others - this was put in to limit false data that was causing flights to jump around all over the planet.

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    • #3
      Most important is line of sight. But of course hardware is important as well and elevation will increase line of sight.

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      • #4
        Height is king for ads-b receiving.

        But there will be a limit to how far your can see. Normally around 250-300nm is the standard quote for range, and also the effect of curvature of the Earth has its effect. But standard doesn't apply to your case as your are going to be 1900ft ASL. I am not sure who has the highest FR24 antenna but yours probably will be on top of the list. There is a software to calculate range around the best antenna thread which is buried somewhere and I couldn't locate it just yet. I will have a dig. We will know the range once your set up goes online at the peak.

        Here is a quote by abcd567 about range: http://forum.flightradar24.com/threa...ll=1#post43772

        Oh Mike also posted too... Different people different opinion haha.
        Last edited by North Borneo Radar; 2014-03-22, 07:29. Reason: grammar, typo

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        • #5
          Right, so the consensus does seem to be pointing toward line-of-sight.

          BTW, if you're wondering whether I plucked those range figures out of thin air, I determined them by 'print screen'ing the data as it changed on several flights until they disappeared, then using the coordinates and Google Earth's ruler tool to measure the distance between the receiver and the last positions of the aircraft.

          The longest range via this method was 551 km, but I don't really know how accurate that can be.

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          • #6
            Height is not so important. Increasing antenna elevation from 1000 to 2000 feet will increase your range only by about 2-4%. So it's all about sight.
            But of course sight often comes together with elevation.

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            • #7
              Originally posted by North Borneo Radar View Post
              Height is king for ads-b receiving.

              But there will be a limit to how far your can see. Normally around 250-300nm is the standard quote for range, and also the effect of curvature of the Earth has its effect. But standard doesn't apply to your case as your are going to be 1900ft ASL. I am not sure who has the highest FR24 antenna but yours probably will be on top of the list. There is a software to calculate range around the best antenna thread which is buried somewhere and I couldn't locate it just yet. I will have a dig. We will know the range once your set up goes online at the peak.

              Here is a quote by abcd567 about range: http://forum.flightradar24.com/threa...ll=1#post43772

              Oh Mike also posted too... Different people different opinion haha.
              1900 meters - not feet ...

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              • #8
                Originally posted by peterhr View Post
                1900 meters - not feet ...
                My bad thanks for correcting typed in a hurry when having a short break at work.

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                • #9
                  Just make sure you have good quality coax cable, so your not imposing unwanted losses is about all i have to add.
                  T-EGLF8

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                  • #10
                    Originally posted by BPO View Post
                    Which is more important: Hardware, sightlines or elevation?
                    The answer is "yes". Everything matters.
                    • While people have seen good results using inexpensive DVB-T dongles and the inexpensive, untuned antennas included with them, using purpose-built gear will pull in more signal.
                    • Since ~1GHz frequencies are all line-of-sight, putting your antenna where it can "see" more planes is vital. No antenna, feed line or radio can see through a mountain.
                    • Elevation can help improve sight lines by putting the antenna above obstructions.

                    Putting your antenna at the top of a mountain will not help much in receiving planes at cruising altitudes. But it can give you line-of-sight view of nearby airports, low level traffic patterns around those airports and TIS-B transmitters. Where I live (US), many commercial aircraft use UAT in place of ADS-B. UAT uses a different frequency and modulation, and there are very few hobbyist receivers for UAT. But because the FAA relays UAT broadcasts (using TIS-B) using a frequency and format that I can receive, many planes can be identified this way. I wouldn't be able to get those TIS-B transmissions if I wasn't at a higher elevation that gives me line-of-sight to the airport across town where the TIS-B facility is.

                    In your case, the ability to track flights all the way to/from their originating airports will give you a better picture of each flight.

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                    • #11
                      Thanks for the info. I'm using the stock antenna and 5m cable as supplied by FR24, but I've begun researching possible alternatives such as a 9 dBi model from DPD Productions. I have no idea if it is much of a step up from what I already have.

                      And I must admit to being a little confused by the statement that elevation doesn't offer much of an advantage for tracking high altitude flights; I'd have thought it would be the opposite. The higher one climbs, the further one sees, surely? I assumed the limiting factor would be signal strength, but then I'm new to ADS-B.

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                      • #12
                        Originally posted by BPO View Post
                        I'm using the stock antenna and 5m cable as supplied by FR24, but I've begun researching possible alternatives such as a 9 dBi model from DPD Productions. I have no idea if it is much of a step up from what I already have.
                        First off, if you're using the FR24 equipment, by all means follow their instructions first and foremost! Don't let advice coming from people like me override that.

                        Personally I wouldn't worry too much about antenna "gain" where you are. IMO it's more important to have even coverage at your elevation than it is to count decibels. It's a more complex thing than I wish to get into right now, but there are technical reasons why a basic antenna can be best for your particular circumstance.

                        And I must admit to being a little confused by the statement that elevation doesn't offer much of an advantage for tracking high altitude flights; I'd have thought it would be the opposite. The higher one climbs, the further one sees, surely? I assumed the limiting factor would be signal strength, but then I'm new to ADS-B.
                        It all depends on what you want to see. Climbing to a higher elevation does let you see more land from a given point; the curvature of the earth obscures the land from lower elevations. I predict that your planned vantage point will let your radio "see" faraway airports, and low level air traffic around their terminal areas, which is a Good Thing. But when it comes to "seeing" an airliner at cruise altitude, it's the plane that has the greater vantage point. Raising yourself up to get closer to the plane will reduce the vertical separation a bit. That will give you marginally greater signal strength for planes overhead. And while in theory you can "see" more planes on the horizon, at such great distances the relatively low transmitter power of the planes' transponders becomes more of a limiting factor. Also transmissions from many planes far away can "walk over" each other, making those weak signals unreadable.

                        There are technological ways to take advantage of your elevation to bring in more distant aircraft, but that takes specialist knowledge and, of course, money. Extreme DX can be a lot of fun, but IMO the first step is to get your basic rig up and running. That will give you a good baseline from which to expand your reach.

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                        • #13
                          Thanks for that. So far everything seems to be running well, and I expect a noticeable improvement in coverage when the equipment is moved to the peak. Right now it loses ~6 degrees alt. to the SSW, and a similar amount in a narrow sliver to the NNW, but otherwise it's open terrain, and the next nearest obstruction is Mount Cook, due N. Even that obscures no more than 1-2 degrees alt. at most. At the peak itself there are effectively zero obstructions in any direction.

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                          • #14
                            Originally posted by Speed Daemon View Post
                            It all depends on what you want to see. Climbing to a higher elevation does let you see more land from a given point; the curvature of the earth obscures the land from lower elevations. I predict that your planned vantage point will let your radio "see" faraway airports, and low level air traffic around their terminal areas, which is a Good Thing. But when it comes to "seeing" an airliner at cruise altitude, it's the plane that has the greater vantage point. Raising yourself up to get closer to the plane will reduce the vertical separation a bit. That will give you marginally greater signal strength for planes overhead. And while in theory you can "see" more planes on the horizon, at such great distances the relatively low transmitter power of the planes' transponders becomes more of a limiting factor. Also transmissions from many planes far away can "walk over" each other, making those weak signals unreadable.

                            There are technological ways to take advantage of your elevation to bring in more distant aircraft, but that takes specialist knowledge and, of course, money. Extreme DX can be a lot of fun, but IMO the first step is to get your basic rig up and running. That will give you a good baseline from which to expand your reach.
                            I must admit I was a bit doubtful about this, but now I'm beginning to see what you mean. I watched an Auckland-Melbourne flight being tracked by an Auckland (airport?)-based receiver and the reach was impressive (~430 km+), despite the fact that there's almost no real elevation to speak of in the Auckland region. Ditto one in the Napier area, as well as the Christchurch-based receivers. None of those are likely to be at substantial elevations, yet all are very close to the kind of ranges I'm detecting.

                            Interesting stuff!

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                            • #15
                              You are reaching far further than most of us based in CHC now. (or at least being attributed to)

                              I use to have my antenna above peak level of the roof on the back of the sky dish mount. But its now ground pole based, and just peaks the roof ridge on the eastern side. Even at that position I get ground traffic bursts at the airport and as far as the waypoints off the coastline (from kaiapoi). The only thing seems to be the alps stopping me now. As I raise it a little more I gain a few kms
                              Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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