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Thread: best antenna

  1. #2681
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    I have a few months ago been selected to host a FR24 box(F-KENL1). Since then I have been experimenting with other antennas and playing around with a flightaware dongle on a raspberry pi using Piaware.

    I have made three coco antennas recently. all using TFC-T10 RG11 tri shield coax with 85% VF

    an 8 element (7 plus top that is 1/4 / 1/4 stinger that shorted) (116.75mm)
    12 element same thing
    8 element with the other calculation in this thread that used a longer wavelength for 1/2 wave (maybe 124 or 126mm)

    Using the FR24 antenna as a base plot, I got these

    FR24 - 450 msg/sec, 240 miles -79 ac tracked
    8 element 116.75mm -420 msg/sec, 240 miles, 91 ac tracked,
    8 element with longer wavelength - 350 msg/sec, 170 miles, 81 ac tracked
    12 element 116.75 - 370 msg/sec, 210 miles, 87 ac tracked (maybe not tracking good right overhead since higher gain)

    NOTE - the FR24 is 5ft higher then the rest of the coco antennas since it has the best spot on the mast to mount it so it can see better over the pole barn in the next lot to the north. Every other direction has trees so north is the best direction I receive from

    Dont have any better measurements, but thats the best I have without nice test equipment. Not using a preamp or any sort of tuning adjustment, just rg6 30ft length straight to the flightaware dongle.

  2. #2682
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    I've got a weird issue. My antenna is on a tower on a remote hilltop at 1400 feet, it's all solar powered and wifi linked. The tower is a wind up and goes from 20 foot to 50 foot. Over the past couple of years several times I have wound the tower up to try to get more range from my FR24 box. The FR24 antenna has pride of place on top of the tower. This is the weird thing ... when I wind the tower up .. every time I drop about 10 - 20 miles in range ! I normally get 200-205 miles max range with the tower down... when I wind it up I get only get 180 -190nm. I have tried different coax, including LD4-50 Heliax and even at one time I mounted the FR24 box at the top of the tower with just a couple of meter of coax. Always the same .. less range with height .. its not coax loss.

    What could it be ? There is a commercial tower about 200 feet away but it is over 300 feet high, I can't imagine that I am getting up into its signals and anyway I believe everything on that tower operates at 2.1 Ghz which should not hurt 1 Ghz. There are mobile phone towers about 3 kms away but when I put another receiver on the antenna and listen to 1090 I don't hear any interference. My only other thought is that with the extra height the angle of radiation is dropping down to the horizon where there are mountains in all directions.

    Anyway I have a low noise amp on the way and will add that to the system and keep playing ... it has a highpass filter so that might help if it is interference.

  3. #2683
    Captain abcd567's Avatar
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    F-YMEN3
    If you are going to use filter, use band-pass filter. Narrower the band, better the filtering.

    There are many types of band-pass filters such as Cavity Filter, Ceramic Filter, SAW filter, LC filter, and Stub filter.
    Last edited by abcd567; 2017-05-02 at 02:21.

  4. #2684
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    Actually it is a band pass, SAW filter, my mistake.

  5. #2685
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    If there is suspicion of interference, which is definitely a risk in your location, try a narrow cavity filter first. Absolutely no amp/lna, regardless of if it comes with some kind of filter or not. a Good cavity has under 1 dB of insertion loss, much better than a SAW and you can live with that. Don't add more active equipment.

    /M
    F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESSL4, F-LFMN3
    P-ESGR, P-ESIA, P-ESIB,

  6. #2686
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    Quote Originally Posted by F-YMEN3 View Post
    I've got a weird issue. My antenna is on a tower on a remote hilltop at 1400 feet, it's all solar powered and wifi linked. The tower is a wind up and goes from 20 foot to 50 foot. Over the past couple of years several times I have wound the tower up to try to get more range from my FR24 box. The FR24 antenna has pride of place on top of the tower. This is the weird thing ... when I wind the tower up .. every time I drop about 10 - 20 miles in range ! I normally get 200-205 miles max range with the tower down... when I wind it up I get only get 180 -190nm. I have tried different coax, including LD4-50 Heliax and even at one time I mounted the FR24 box at the top of the tower with just a couple of meter of coax. Always the same .. less range with height .. its not coax loss.

    What could it be ? There is a commercial tower about 200 feet away but it is over 300 feet high, I can't imagine that I am getting up into its signals and anyway I believe everything on that tower operates at 2.1 Ghz which should not hurt 1 Ghz. There are mobile phone towers about 3 kms away but when I put another receiver on the antenna and listen to 1090 I don't hear any interference. My only other thought is that with the extra height the angle of radiation is dropping down to the horizon where there are mountains in all directions.

    Anyway I have a low noise amp on the way and will add that to the system and keep playing ... it has a highpass filter so that might help if it is interference.
    Id imagine you are experiencing swamping... an overload of signals from the other towers - it doesn't matter that they are using different frequencies, you receiver employs lots of intermediate frequencies, and probably less than perfect design, as such any strong signals will effect the operation and sensitivity of your receiver.
    You may add filters and cavities etc, but I suspect your on a hiding to nothing... just find a good compromise position for the gear and live with it !

  7. #2687
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    Quote Originally Posted by Rooster View Post
    Id imagine you are experiencing swamping... an overload of signals from the other towers - it doesn't matter that they are using different frequencies, you receiver employs lots of intermediate frequencies, and probably less than perfect design, as such any strong signals will effect the operation and sensitivity of your receiver.
    You may add filters and cavities etc, but I suspect your on a hiding to nothing... just find a good compromise position for the gear and live with it !
    Yeah, its a shame we can atleast hear the receiver in the FR24 boxes ... a spectrum scope would be even better.

    It is interesting that the tower that is 3km away (actually several towers) is hidden by another mountain .. I can just see the very tip from ground level ... as I wind up my tower I imagine the coms towers in the distance comes into clear view of the 1090 antenna.

    Anyway I have already ordered one of these - EDIT can't post the link but its the LNA from Uptronics made specifically for 1090Mhz

    I guess I'll see what happens with that installed and at different heights. If it works best at a lower height, then so be it.

  8. #2688
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    Quote Originally Posted by Rooster View Post
    Id imagine you are experiencing swamping... an overload of signals from the other towers - it doesn't matter that they are using different frequencies, you receiver employs lots of intermediate frequencies, and probably less than perfect design, as such any strong signals will effect the operation and sensitivity of your receiver. You may add filters and cavities etc, but I suspect your on a hiding to nothing...
    Well, something tells me that you lack actual experience of these scenarios, because your theories are missing one crucial point.

    While it's quite possible that strong RF interference on intermediate frequencies can have an affect on RX performance, unless you are co-sited with very strong transmitters, which was not the case here, the main way for such interference to get inside your receiver is through the antenna and antenna port. A cavity bandpass on the antenna cable will very effectively block all such interference.

    For a signal to go straight through an aluminum box, or picked up by DC or ETH cables, the field strength would have to be VERY high, certainly not a problem from a tower 3km away.

    The best test for this and similar issues is to have a god cavity filter to test with. In practice, it solves 90% of all interference problems.

    /M
    F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESSL4, F-LFMN3
    P-ESGR, P-ESIA, P-ESIB,

  9. #2689
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    Quote Originally Posted by MrMac View Post
    Well, something tells me that you lack actual experience of these scenarios, because your theories are missing one crucial point.

    While it's quite possible that strong RF interference on intermediate frequencies can have an affect on RX performance, unless you are co-sited with very strong transmitters, which was not the case here, the main way for such interference to get inside your receiver is through the antenna and antenna port. A cavity bandpass on the antenna cable will very effectively block all such interference.

    For a signal to go straight through an aluminum box, or picked up by DC or ETH cables, the field strength would have to be VERY high, certainly not a problem from a tower 3km away.

    The best test for this and similar issues is to have a god cavity filter to test with. In practice, it solves 90% of all interference problems.

    /M
    Yea... alright, ive no need to banter Cv's :-(

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