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Thread: Improving my coco antenna

  1. #11
    Captain fungus's Avatar
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    Quote Originally Posted by PiRad108 View Post
    I have been having fun building and learning about antennas the last few days. A few disappointments along the way as well, my first antenna 16 element coco array failed on examination I found it was the severe heat we have been having the joins had expanded and got slippery and several had separated, lesson use heatshrink instead of electrical tape. I am awaiting the better dongle from jetvision so my two new antennas have been built with SMA connectors and are yet to be tested one is a simple spider thanks to abcd567. The other after making a decision to switch to 50 ohm cable is an 8 element coco made from RG8 this presented a few challenges due to the thickness of the cable it is very rigid, it also has a 2 mm solid copper core. I cut groves in the outer sheath at each end of the elements then pushed the central core in to the incisions, crimped it with pliers then zip tied, tested, heat shrinked and zip tied the heat shrink with another round of zip ties. I then enclosed it in a PVC tube and popped a connector on the tail.
    Just exercise a little caution when using PVC conduit to enclose your coco. Some, but by no means all, PVC conduit can degrade the signal you're attempting to receive. There is plenty of advice on the net re testing of these conduits but I've found the safest (buggered if I'm sticking it in the microwave oven) is to try it inside the property with and without it for comparison before hoisting it up the mast.

    Some also require painting as they aren't UV protected and that too can be problematic depending on the paint used.

    Sounds like you've got everything else pretty well covered. It is indeed fun isn't it?

    Regards,
    Gregg
    Last edited by fungus; 2018-03-04 at 01:36.
    YSSY2/T-YSSY4 [SBS-1 Basestation w/- SSE-1090 SJ Mk2 Antenna (Thanks Delcomp) ] [Uniden UBCD996T w/- 16 element Wideband Discone VHF/UHF Antenna, and tuned 108MHz-137MHz Airband Antenna] [Trialing a home-brew 1090MHz collinear antenna]

  2. #12
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    Quote Originally Posted by PiRad108 View Post
    ... my first antenna 16 element coco array failed on examination...
    Jeez, even with a full RF lab it's almost impossible to get a collinear with that many elements in phase. IF you are building "blind", try 3-4 elements. If you have a good SWR meter, maybe 5-6.

    /M
    F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESNV3 F-ESSL4, F-LFMN3
    P-ESGR, P-ESIA, P-ESIB, P-ESGF

  3. #13
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    Quote Originally Posted by MrMac View Post
    Jeez, even with a full RF lab it's almost impossible to get a collinear with that many elements in phase. IF you are building "blind", try 3-4 elements. If you have a good SWR meter, maybe 5-6.

    /M
    I am just starting to learn what I does and does not work as you know there is lots of misleading info out there. On that note my 8 element RG8 coco which is on its first day test in the carport because it is raining at the moment is getting the best results so far for that location having used the supplied short whip antenna, and a Spider in that location which only has decent Northern line of sight and getting 40 NM max, this one has already given me 62 NM.
    T-YBBN167 PiRad108

  4. #14
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    It's better to start with something easier!


    The problem is, even if you DO have an SWR meter, the small phase differences messes with the radiation pattern so that all that theoretical gain will never materialize. This is not visible on SWR, it can be perfectly resonant but still not give the expected gain in any direction.

    I have seen this well demonstrated, worked for a major antenna manufacturer and we made a 10dB collinear. It was a b*tch to assemble correctly and we had a fully automated compact range (anechoic chamber) with an ABB robot that made automated over-night 360x360 gain measurements that we invested 3 million USD in. Unless you have access to that kind of equipment that can actually measure gain in different directions, it WILL be sub-optimal.

    There is a reason both FR24 and Flightaware decided that the best performance comes from 5-6 dB collinear antennas. I know for a fact that FR24 tested a lot of different ones before they made that choice.


    BR /M
    F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESNV3 F-ESSL4, F-LFMN3
    P-ESGR, P-ESIA, P-ESIB, P-ESGF

  5. #15
    Captain abcd567's Avatar
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    @MrMac:
    Fully agree.

    Flightaware 26 inch Antenna: Wire Collinear, with Decoupling Sleeve.


  6. #16
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    Quote Originally Posted by fungus View Post
    Just exercise a little caution when using PVC conduit to enclose your coco. Some, but by no means all, PVC conduit can degrade the signal you're attempting to receive. There is plenty of advice on the net re testing of these conduits but I've found the safest (buggered if I'm sticking it in the microwave oven) is to try it inside the property with and without it for comparison before hoisting it up the mast.

    Some also require painting as they aren't UV protected and that too can be problematic depending on the paint used.

    Sounds like you've got everything else pretty well covered. It is indeed fun isn't it?

    Regards,
    Gregg
    Gregg, I'm a late-comer to this but have built myself an 8 element CoCo out of left-over RG6 (left over from when we'd cancelled our Foxtel) using the dimensions given by abcd in the other thread. I've got it installed in some Holman 15mm PVC-U pipe that I got from Bunnings. As far as I can tell there doesn't seem to be too much signal degradation - I'm getting around 130-140Nm with about 2m sticking out of a J-bracket that I bought from Jaycar. Next step is to add one of those 20db satellite amps that I got off ebay for around $6 and a Kingray power injector that I bought from Jaycar.

  7. #17
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    Quote Originally Posted by petercr View Post
    ... 8 element CoCo ... 130-140Nm ... 20db satellite amps
    Get any 5dB antenna that is tuned properly and you will get 200+ nm with a decent cable and an FA Prostick.

    Your system is underperforming and adding a SAT amp is not going to solve that unless you have terribly high cable attenuation today.

    /M
    F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESNV3 F-ESSL4, F-LFMN3
    P-ESGR, P-ESIA, P-ESIB, P-ESGF

  8. #18
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    Quote Originally Posted by MrMac View Post
    Get any 5dB antenna that is tuned properly and you will get 200+ nm with a decent cable and an FA Prostick.

    Your system is underperforming and adding a SAT amp is not going to solve that unless you have terribly high cable attenuation today.

    /M
    I can vouch for that. The FA antenna opened my eyes yesterday, right after that I was turning down the Pro Stick gain!

  9. #19
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    Quote Originally Posted by MrMac View Post
    Get any 5dB antenna that is tuned properly and you will get 200+ nm with a decent cable and an FA Prostick.

    Your system is underperforming and adding a SAT amp is not going to solve that unless you have terribly high cable attenuation today.

    /M
    I'm trying the least costly options first - if you notice above the coax cost me nothing and the amp only cost $6 (the power supply was lying around from a previous TV installation). Since ordering that, I've also ordered a FA Prostick+ from a local Australian supplier which I'm hoping won't take too long to arrive. The antenna would be the last option as that'd be another $100 on top.

    All the cabling is RG6 with the run from the antenna connector to the DVB-T stick being quad-shielded and the length being kept as short as possible. There's also local geographic and arboreal conditions that I've had to take into account so I humbly think 140Nm isn't too bad considering.
    Last edited by petercr; 2018-03-21 at 20:50.

  10. #20
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    @petercr:
    I suggest you determine the maximum range you can get at your location using method described in the following thread. This will serve as a reference for you to judge how good or bad your system is.

    What is the Maximum Range I can Get?

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