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Thread: Start of my RPi journey

  1. #81
    Flight attendant
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    Apr 2013
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    Brisbane, Australia
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    97
    Quote Originally Posted by wiedehopf View Post
    Get yourself some filtering and amplification: https://www.rtl-sdr.com/new-product-...mhz-ads-b-lna/

    Then you can use your old coax (with the amplifier close to the antenna).
    The filtering is probably what you need the most with a discone antenna.
    So, the filter in the flightaware stick not good enough...or in the wrong place?

  2. #82
    Captain
    Join Date
    Apr 2018
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    868
    The filter only comes after the internal LNA, which is often too late.
    With a discone i suspect the internal LNA will get overloaded and produce noise on all frequencies.

    But obviously it's also good to help with your coax to have some amplification near the antenna.
    Not sure if you can access the coax after maybe 2 to 5 m of length and put the LNA there without going onto the roof?

    You can check the situation with the noise like this: https://forum.flightradar24.com/thre...ignals-In-Area

    Even if the noise is not a problem, it will help greatly to compensate the coax loss even if you can only mount it half way between receiver and antenna.
    (Optimal is closer to the antenna, but i'm sure you are aware if you have done radio stuff before )
    Last edited by wiedehopf; 2019-10-17 at 08:01.

  3. #83
    Flight attendant
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    Apr 2013
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    Brisbane, Australia
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    Hi wiedehopf, yes I can get to the coax, approx. 3 metres directly underneath the present mast in the roof cavity, so my wife will be happy i am not on the roof...At present, this RG6 feeds my airbands scanner. I simply removed the BNC fitting from the scanner input and connected it to the Flightaware dongle. I had a look at the link...Do i need a filter etc... People seem to put them, in front of the dongle, or near the mast or....Maybe after all this manoeuvring to use my discone, I should get/make a better antenna. If i want to fit a filter on the coax in the roof cavity, I will use F connectors.

    My immediate plan is to create the four leg spider (got materials today) and try it in my office to see what reception it gets. I suspect though, I may end up on the roof and fit it up there next to my discone. Bring its separate RG6 into the roof cavity. Then "chop" the antenna cable that connects to my scanner or RPi, so that I can use this lead for both scanner and ADS-B antenna by swapping over connections in the roof cavity. I will use F connectors.

    When I looked at the graph/stats for the signal, (see my post page 8) it seems very tight compared to others that span the entire graph. Maybe because of the Discone (https://www.diamondantenna.net/d130j.html) with such a wide band and very low gain!) Would providing a different whip length (68mm) help the ADS-B signal on the discone? I have a spare set of the radial arms which I could also cut down to suit, turning my scanner discone into a ADS-B antenna?
    Last edited by POR911; Yesterday at 04:40. Reason: Later thought

  4. #84
    Captain
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    Apr 2018
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    Yeah making the discone more like a spider antenna will probably help.

    The signal spread in the graphs can be low because of noise for example.
    Or there may just not be enough signal left at the end of the coax.

    In either case the amplifier/filter i linked should fix both problems.

    Yeah a self-built antenna without it being on the roof can also get good range.
    Might be that the coax you are using is just killing too much of the signal.
    Building your spider and trying it in the office will be a good test for that.

  5. #85
    Flight attendant
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    Apr 2013
    Location
    Brisbane, Australia
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    97
    The RPi is working great, and I am now feeding Fr24 following very helpful advice on this forum. I received my welcome email from FR24 with my sharing key and radar code. I am not sure how the free business subscription kicks in. FR24 provided a 'free business subscription' link, (https://www.flightradar24.com/premiu...p?account=free) but it seems to take me to the usual subscription page.

    I was also automatically resubscribed to the Gold subscription in May 2019. Is the balance refunded or frozen?

    Because I will be changing antenna's, that will no doubt cause disruptions to the feed, what leeway is given for feeder being down before you get chopped? maybe always keep a basic antenna connected, while setting up "improved" antenna, and do a quick swap over!!

    Over the next month or so, I will be experimenting with different antenna's and setups. I will report back here with results. First tests will be:
    1. Using present Discone. It see's most a/c that FR24 indicates, though usually only within 120kms. I will use it for a few weeks.
    2. Using present discone setup, but changing its single 900mm whip, 8 x 280mm horizontal ground plane and 8 x @ 45 degree 820mm radial elements to ADS-B length. Is there a benefit of using full 275mm wave length or 1/2 or 1/4? Certainly, 1/4 is easier to fabricate.
    3. As my discone will become an 8 leg spider, I don't see the benefit of building another?
    4. Using some sort of amplifier/filter close to the antenna mast.
    Last edited by POR911; Today at 01:49. Reason: later thought

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