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Advice on sharing RX antennas with 3 SDRs in the most effective way



  • Hi,

    You could try building these designs

    BN73-202 with four turns on the second transformer rather than two (to improve the LF performance), the -1dB points are at 20KHz and 70MHz.



    BN73-202 7 + 2 x 5 turns = 3.1dB loss plus -1dB down @ 20KHz & -1.5dB @ 30MHz

    I twisted the wires (I use PTFE or Kynar covered wire wrap, insulation not particularly critical) with an electric drill, about 4 or 5 turns per inch. This improves the coupling between wire pairs and halves the time taken to thread the wires through the holes in the binocular cores.

    I've also got a design for a simple 4 way split that I built somewhere. I must dig out my notes and try to write this up properly.


    Martin - G8JNJ
  • edited July 2019
    This afternoon I played with various 4 way splitter designs.

    Note that all 4 way splitters have a minimum of 6dB through loss, regardless of whatever is connected, so you should only use them after a suitable amplifier with about 10-12dB gain.

    All the designs I tried tended to be quite difficult to setup correctly, and this would be especially problematic if you didn't have access to suitable test equipment.

    Problems include poor match and lumps and bumps in the frequency response.

    However if you want to build something simple that works, this is about as good as it gets and should only cost a few dollars to construct.

    Input and output match is typically better than 1.5:1, the only downside is that the port to port isolation is worst case 12dB.

    The more complicated designs can achieve better than 20dB, but use two more transformers with different winding ratios, have greater losses and are more difficult to get a good frequency / amplitude response.

    The choice is yours :-)


    Martin - G8JNJ
  • edited July 2019
    Message removed
  • edited July 2019
    Martin, gear icon top right of your post(s), "Option", "Edit", you get 24hrs to correct the post.
    You always post good info so it's worth correcting the first one.

    Look at the "edited" time on this post.
    it should be a little after the post time.
  • Thanks Powernumpty. I'd looked for the edit cog just after posting, but couldn't find it. Turns out you have to move your mouse over the message text box before it appears.
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