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Coax length?

Discussion in 'CB Antennas' started by 85Blazer, Sep 22, 2018.

  1. 85Blazer

    85Blazer New Member

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    I just was wondering what is the max length of coax I can or should run? The reason being I just got a solarcon a99 and I'm trying to decide where to mount it. Any thoughts?


     

  2. midnight special

    midnight special Well-Known Member

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    and the fight is on in 3 2 1,,,,,
     
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  3. sp5it

    sp5it Master of puppets

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    Max length? As much as needed.
    I use 250m coax to one of my antennas.
     
  4. jon666

    jon666 Sr. Member

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    there is no max. just use what you want or need
     
  5. 85Blazer

    85Blazer New Member

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    Food for thought. Thanks
     
  6. tba02

    tba02 WOOF

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    Minimum suggested length is a few feet longer than you need to make the connection.
     
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  7. 85Blazer

    85Blazer New Member

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    Hahaha, thanks I needed that.
     
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  8. jessejamesdallas

    jessejamesdallas Sr. Member

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    If your antenna is 55' away, but someone tells you, you can only use 50', "what would you do?" Stick the radio out on the side of the tower?
    [​IMG]
     
  9. 164 northern cal

    164 northern cal Active Member

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    I have several coax leads all are around 160ft. I will stick and antennas high as I can get it into the air. My A99 tip is 108 ft. in the air. It is all about how you can improve the signal. Off grid in the boonies in the mountains is me all the way, and always trying to better the signal in and out.
     
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  10. 543_Dallas

    543_Dallas Sr. Member

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    It depends on what kind of coax you are using and how much loss is acceptable to you. Here's something to help you decide.

    https://www.qsl.net/co8tw/Coax_Calculator.htm
     
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  11. Redbeard U812

    Redbeard U812 Active Member

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    Old note in The AARL Antenna Book, Hall Edition, page 111 has some information that may be of use to you. The diagram shows Length in Feet to avoid exact resonance at frequencies from 3.5 to 29.7 MHz. Although it's disputed, remember this was probably printed from actual lengths that had been used without the use of antenna match boxes. I figured my length needed and just so happens it fell on one of the "best match" locations.
     
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  12. The DB

    The DB Sr. Member

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    If we lived in a perfect world where coax had no losses, then it wouldn't matter. However, it really does depend on how much loss you are willing to accept.

    Lets say you are transmitting 100 watts into 100 feet of:
    Belden 9201 (RG-58) you will get 63.29 watts out
    Belden 9258 (RG-8X) you will get 69.854 watts out
    Belden 8267 (RG-213) you will get 78.543 watts out
    Times Microwave LMR-400 you will get 86.403 watts out
    NOTE1: Data above from https://www.qsl.net/co8tw/Coax_Calculator.htm
    NOTE2: Data above assumes a perfect SWR match at freqnecy 27.18 MHz.

    So to answer the question of how long of a coax run you can effectively use depends on the length you need to run and the type of coax you plan to use. With the example of the Belden 9201 RG-58 coax above, after 100 feet of coax you have effectively lost over 1/3 of your transmitted power before any of it ever makes it to the antenna.

    I guess what I am trying to say is, to give you good advice, we really need more information on the type of coax you plan to use and the different lengths of coax needed, as well as the different heights of the antenna in question.


    The DB
     
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  13. dave457

    dave457 Well-Known Member

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    Do you think between 63 and 86 watts the receiving end can hear a difference?
     
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  14. The DB

    The DB Sr. Member

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    I love the assumptions being made...

    Here, let me put your mind at east as you have clearly not seen the many times I have talked about such things in the past.

    No, I not only not not think, but I know that a receiving station won't notice this difference. But then, that wasn't the goal or point of my post to begin with...

    I was simply trying to show a potential difference in a way that someone who is not as technically minded as some of us could understand, and use that as a springboard to ask for more information so we can provide better guidance.


    The DB
     
  15. dave457

    dave457 Well-Known Member

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    I knew the answer and what your point was, was just throwing it out there as some might look at it in that point of view
     
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