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Collinear antenna question

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  • Collinear antenna question

    I'm currently running the standard DVB-T desktop antenna on an RTL-SDR adapter and getting reasonable results considering it's indoor.

    I've tried to make a few different antennas, including a collinear antenna with RG6 cable, but currently none are giving better results than the small DVB-T antenna (or even working at all).

    My current attempt has 8 segments at 11.6 cm each, feeding the centre conductor between the insulation and braiding of the next segment. That seems to have gone well with no shorts across the length, but still not a great antenna.

    The other bits consist of:

    USB DVB-T/RTL-SDR adapter
    MCX to Belling-Lee RF adapter (PAL TV RF) (because this is what I have to hand)
    Coax
    Belling-Lee to F-connector adapter
    F-connector on the bottom of the antenna

    The main questions are:

    Is there anything wrong with this?
    Should I have a λ/4 type whip on top?
    Should the bottom of the whip be soldered to the braiding?

    There's obviously something not right because even indoors I'd expect better performance than the desktop antenna.
    Last edited by ant_thomas; 2015-05-29, 09:31.

  • #2
    Belling-Lee connectors are a pain. My dongle has one and I will be replacing it with F-type as soon as the fittings arrive.
    I would start with 3 or 4 elements in the co-linear. Unless your construction is spot-on, the extra elements will only make thinks worse.

    The other problem will longer antennas is the likely-hood of getting overloaded by other frequencies.
    I have a transmitter on 146MHz very close by and when ever it transmits, the ADS_B would stop totally.

    I fixed this problem by installing a quarter wave stub in the coax line.
    See this post (a few posts down):
    8609-LC-filter-LNA-w-SAW-or-something-else

    I have since added a pre-amp and the overload problem is back (but not as bad). The next step will be a decent filter.

    I am still using a 4 element co-linear - any longer and it would move around in the wind too much.

    Jim

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    • #3
      I have virtually the same configuration than you but the range is twice as long with original DVB-T -antenna than with my home built antenna (even if the location of my DIY antenna is significantly better...)

      Guess I have to measure if there is something wrong with my antenna, if not then I'll try to built a new antenna.

      Comment


      • #4
        for the cost of trying keep building them, your technique will improve as you do.
        T-EGLF8

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