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Thread: Serious Question about my antenna

  1. #1
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    Serious Question about my antenna

    im building a collinear coaxial antenna at home and i dont get any 1090 mhz signal, its a 8 elements antenna (i did all the calculations and the length of each elements is 116mm ), but my question is... Im using 8 elements and in the end of the 8th element its the feeder cable (7elements and then the feeder) should i add one more element? so theres 8 elements + the feeder cable? is that right? I mean, once i add the feeder cable to the 8th element, my multimeter read theres continuity... should NO or Should be continuity at the end?

    Thanks

  2. #2
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    with design you say you have

    if you measure at just one end of the cable should be no continuity between the centre and the shield.

    if you connect one probe to one end of the cable and one to the other end of the cable - there should be continuity from the shield to the centre.

  3. #3
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    Quote Originally Posted by peterhr View Post
    with design you say you have

    if you measure at just one end of the cable should be no continuity between the centre and the shield.

    if you connect one probe to one end of the cable and one to the other end of the cable - there should be continuity from the shield to the centre.
    Doesn't compute with me

    Maybe should read
    If you connect one probe to one end of braid and the other probe to the other end of the braid - there should be continuity
    If you connect one probe to one end of the centre and the other probe to the other end of centre - there should be continuity
    If you connect one probe to centre and one probe to shield - either end - there should be no connectivity

    Mike

  4. #4
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    I dont get it... Here's an example i took for another website: below, theres a 4 element CoCo (Coaxial Collinear) antenna (shouldn't have continuity) But then he added one more cable which is the actual cable to connect to the dongle so that added one more element and because the # of elements is impair there's continuity, am i right?
    4 elements CoCo
    DSC_0032-300x225.jpg

    Final Antenna
    DSC_0033-300x225 cable.jpg

    You see what i meant?

    Thanks
    Last edited by Adelgallego; 2014-08-30 at 14:08.

  5. #5
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    It's not as simple as it seems...

    If you are asking should a meter show a connection between the core and the braid - the normal answer is no, but

    it is possible to top off you coco with a half length element where the core is connected to the braid at the end - then a connection would show on a meter - but at the signal frequency it behaves differently.

    The you tube video that shows how to make these says test to ensure there is no connection (between braid and core) each time you add a stage to check that you haven't made a mistake.

  6. #6
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    Quote Originally Posted by peterhr View Post
    It's not as simple as it seems...

    If you are asking should a meter show a connection between the core and the braid - the normal answer is no, but

    it is possible to top off you coco with a half length element where the core is connected to the braid at the end - then a connection would show on a meter - but at the signal frequency it behaves differently.

    The you tube video that shows how to make these says test to ensure there is no connection (between braid and core) each time you add a stage to check that you haven't made a mistake.
    So between braid and braid there should be a connection? And between braid and core shouldn't??

    Thanks for the help

  7. #7
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    I just took a couple pics to try to make you see what i meant and to get some help building this... what's next? what should i do?

    8 Elements antenna:
    Foto 30-08-14 7 42 41 p.m..jpg

    8 Elements + feeder line (is that right?):
    Foto 30-08-14 7 42 26 p.m..jpg

    A better look:
    Foto 30-08-14 7 42 49 p.m..jpg

    116mm length (L=(0.5(half wavelength))*(275mm (Lambda))*0.85(Velocity Factor of 75ohms RG6U cable)=116 mm(length of each element)(I Used a calliper to measure the elements):

    Foto 30-08-14 7 42 54 p.m..jpg

    The feeder line:
    Foto 30-08-14 7 43 05 p.m..jpg

  8. #8
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    More pictures with the multimeter:

    Making sure theres no continuity between inner cores (idk why its upside down):
    Foto 30-08-14 7 51 59 p.m..jpg

    Continuity between inner core and shield:
    Foto 30-08-14 7 52 21 p.m..jpg

    There's continuity between inner cores once i connect the feeder cable:
    Foto 30-08-14 7 53 47 p.m..jpg

    And this is how i connected it:
    Foto 30-08-14 7 57 22 p.m..jpg

    Please help

  9. #9
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    If you have just the feeder cable, then the core one end is connected to the core the other (Inner - Inner)

    if add one section, then the core one end is connected to the braid the other (Inner - Outer)

    if you add another section, then the core one end is connected to the core the other (Inner - Inner)

    if you add another section, then the core one end is connected to the braid the other (Inner - Outer)

    and so on

  10. #10
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    But what about this configuration? It doesn't matter if there's continuity between inner - inner? what does really matters? Beside the correct length?

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