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

  1. #11
    Flight attendant
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    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.


  2. #12
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    Quote 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.

  3. #13
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    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.

  4. #14
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    Quote 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!

  5. #15
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    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

  6. #16
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    Quote Originally Posted by Oblivian View Post
    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
    From my observation T-NZCH2 also has good range towards the Southern Pacific Ocean. But I haven't been looking into NZ a lot really. BPO got me all looking into NZ area to see what kind of range is capable for his receiver.

    Any plans to raise your antenna to a better height or this is your permanent installation Oblivian? Incidentally, my application for FR24 receiver got approved. Wasn't expecting it really as I gave up after not hearing totally for months.

  7. #17
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    Quote Originally Posted by North Borneo Radar View Post
    From my observation T-NZCH2 also has good range towards the Southern Pacific Ocean. But I haven't been looking into NZ a lot really. BPO got me all looking into NZ area to see what kind of range is capable for his receiver.

    Any plans to raise your antenna to a better height or this is your permanent installation Oblivian? Incidentally, my application for FR24 receiver got approved. Wasn't expecting it really as I gave up after not hearing totally for months.
    Indeed, T-NZCH2 does keep filling in a few holes that way now and then, to the range just shy or about the same as BPO (even from a roof peak on single dwelling). However that soon hands over again to the F- boxes, so hard to compare using the online map the exact overlap.

    It's likely to be this way for a while. I would love to stick a 1-2m pole on the peak.. but the owners won't have a bar of it on such a new build the alternate is a pole on the fence beside my window. But the cable would need to be strung across a pathway and being LMR400 need some fairly sizable holes made in the flashing :/

    Other than that I can get a better base and another extension to crank it up another metre or so. However only of real advantage to my own viewing. Still only a supplied beast, so other than a bit of over-head or east coast flights I'm hardly contributing these days, unless any of the others have downtime, there's enough of the new F-boxes around supplying enough data.

  8. #18
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    Quote Originally Posted by Oblivian View Post
    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
    Does all that 'longer range data' count? Doesn't FR24 ignore all uploaded data referring to planes more then 400km from your declared base location - so with CHC being 100km further east the CHC data from le last 100Km might still be what's used... [curious]

  9. #19
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    Quote Originally Posted by peterhr View Post
    Does all that 'longer range data' count? Doesn't FR24 ignore all uploaded data referring to planes more then 400km from your declared base location - so with CHC being 100km further east the CHC data from le last 100Km might still be what's used... [curious]
    Peter,

    You are correct as I understand it in that there is a 400km limit to the uploaded data from any one receiver and for a very good reason. When I first began with my receiver in 2008 some aircraft were displaying erroneous longitude data from them and placing them up to on some occasions some 14,000nm or so out into space (generally in the order of 4,000nm to 7,000nm). These errors were then being transferred to the map and looked dreadful with aircraft displaying (incorrectly) all over the map. Something needed to be done and the uploader software was improved by FR24 to deal with this issue. A much more reliable and accurate map is the end result. This topic is mentioned by others on other threads on the forum. Kinetics were never able to (or just didnt) update their software/firmware to fix this issue, at least for the SBS-1 unit.

    To the subject of the thread, like Oblivian and many others, here in Sydney I have mountains to the west, north and south which block signal. The city to the east and a few hills to boot... and heaps of gum trees etc. So in regard to the topic of this thread I fall into the 'all of the above' category- what is important is hardware, line of sight and elevation (of antenna). I first started with a discone antenna, very poor RG58 cable (as far as signal loss) and a not very high antenna location. Since then I have improved my setup with a 1090SJ antenna (thanks again David), far better and shorter length of cable and a much higher mast. The mast alone has increased my range to a 'best' distance of 444km (primarily to the north) and more importantly has removed a vast amount of signal dropout due to obstructions. A better amp has also helped.
    I'm now seeing departing and arriving aircraft at Sydney (SYD/YSSY) at levels which I never could before. I can see aircraft to the east over the Pacific Ocean on approach and departure which I couldnt previously. But it isnt all great news. To the sth west I've lost some aircraft tracking in some small areas and I think the answer is in the fact that by increasing the mast from 20ft on my roof ridge capping to 30ft I have placed the antenna into the 'shadow' of a few tree canopies that I previously was 'shooting' underneath or aside. There are also many more feeders here so getting onto the map can be a bit of a lottery.

    However the above are some of the reasons why I dont think of the (now) many uploaders in this region (I started as the second feeder here) as 'competition.' I look at it as more of giving me the incentive I need to improve my setup.

    Hope this adds something useful to the discussion.

    Regards,
    Gregg

    NOTE: 400nm = roughly 740km so it's a fair way from 'home' to be picking up aircraft and perhaps, sadly, we dont all live on mountain tops.
    Last edited by fungus; 2014-03-27 at 06:11. Reason: additional info, adjustment and correction

  10. #20
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    Don't get me wrong, this is an unusual situation in that this is a F- receiver mounted on the top of a mountain and has a stupendous range covering almost the whole of south island NZ and a long way out to sea - well over 400km - possibly receiving planes that are beyond the range of receivers much lower altitude actually on the shorelines.

    I was just wondering if some of the data from the mountaintop receiver would be ignored because of the 400km limit
    ... in which case the shore line feeders would still update the server since it is within their 400Km allowance.

    In cases like this is FR24 able to relax the 400Km limit - especially when the feeder is an F- of known quality with a GPS time source, etc.

    (What really would be interesting would be if the limit were replaced by some sort of calculation that said we last got a reading at time t1 and it was located at position p1, the reported position is p2 at time t2, is it possible for the plane to have travelled distance ABS(p2 - p1) in the time (t2 - t1) at a speed of - say 1100km/h)

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