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Base Longest Coax Length Possible?

Discussion in 'CB Antennas' started by ShadeTreeMechanic, Feb 12, 2018.

  1. ShadeTreeMechanic

    ShadeTreeMechanic 808 On The North Side of Dover

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    Hey guys,
    I am planning my new shack in the side room off the living room. I have an existing Star Duster copy about 20ft up on the corner of my detached garage with 100ft of LMR 400. About 50ft of coax is zig zagged and attached to the rafters. If I were to run coax to the new shack, it would be right around 250ft between the garage and the house so maybe 300ft of coax total. Would this be too far and would I be better off putting a pole up the back of the house so it can be closer? Any and all replies welcome.
    Thanks!


     

  2. The DB

    The DB Sr. Member

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    That pushing it even for LMR-400. Even with a perfect SWR match at the antenna side you would have about 35% losses between the radio and the antenna, so with 100 watts of power transmitted you would get about 65 out.

    Source, http://www.qsl.net/co8tw/Coax_Calculator.htm

    [​IMG]


    The DB
     
  3. ShadeTreeMechanic

    ShadeTreeMechanic 808 On The North Side of Dover

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    That's good to know. So it could be done but at a cost. The power loss I could almost live with. The cost of that much coax starts getting expensive real quick too. I would probably be better off putting a pole up the back of the house. I wanted to get a beam anyway so now is my chance. Thanks!
     
  4. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Another not mentioned issue is the DC resistance of the wire. Receive loss would be significant.
     
    543_Dallas and The DB like this.
  5. ShadeTreeMechanic

    ShadeTreeMechanic 808 On The North Side of Dover

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    That's an interesting point. I suppose that I could put an amplifier with a pre amp in the garage where the antenna is. Or am I just grasping at straws here?
     
  6. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    It would be better if the coax is shorter. Would you like getting up and going to the garage just to change a setting on the amp?
     
  7. ShadeTreeMechanic

    ShadeTreeMechanic 808 On The North Side of Dover

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    Yeah a tube amp is out of the question. LOL I already have a nice 50ft chunk of LMR400 to use if I can put the antenna right outside the room where the shack will be. Might put up a small tower. Now I have to go outside and look. Planning and figuring it all out is the fun part. Thanks.
     
  8. tba02

    tba02 WOOF

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    At 100 feet of LMR400 coax, 86% of your output will reach the antenna.
    At 300 feet of LMR400 coax, 64% of your output will reach the antenna.

    For RG-213 the numbers are 78/48.

    If at the same height, I would choose 100 feet, and use any additional length (and $$) to go UP if possible.

    *assumed at 27.200 MHz
     
  9. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    Maybe consider using 450 ohm balanced line but you'll need 9:1 baluns to revert back to coax and bring it to 50 ohms at the antenna. This type of feedline has far less loss than coax especially at long lengths.

    There's more to it than that regarding actually running it so some research and maybe tips and advice from forum members here can help.

    Another alternative is run large heliax cable but it's expensive and so are the connectors.

    Or, just run what you got and it'll work and only you will know the losses. On a 4 watt radio, you might lose up to 2 watts in losses.
     
    ShadeTreeMechanic likes this.
  10. 543_Dallas

    543_Dallas Sr. Member

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    An amplifier in the garage isn't that hard, that's where one of mine is. It is also a tube amplifier. Tune it up once and leave it alone. If you constantly need to retune it needs to be scrapped or repaired. For frequency changes some different colored post it notes can be trimmed and stuck on the face plate for reference points for plate and load settings.

    I have about 80 feet of lmr600 from antenna to the amplifier and probably another 75 feet of lmr400 from my radio through the attic out to the amp. The lmr600 from JefaTech is reasonably priced and their coax seems to be decent quality.

    While running the coax to the garage I ran a couple of cat5 cables for keying the amp and for a remote tuner. Also a couple of extra coax runs for the oscilloscope pick up and bird line section. Getting in the attic sucks so pull more than you think you'll need and leave a couple of pull strings just in case.
     
    ShadeTreeMechanic likes this.
  11. Mustang 131

    Mustang 131 Well-Known Member

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    I run about 350' from my shack to my antenna in my backyard. Invest in some LMR600. I seem to hear and get out ok.
     
    #11 Mustang 131, Feb 13, 2018
    Last edited: Feb 13, 2018
    ShadeTreeMechanic likes this.
  12. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    What about when you change bands?
     
  13. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    That's the way to do it. Height makes might!
     
    ShadeTreeMechanic likes this.
  14. ShadeTreeMechanic

    ShadeTreeMechanic 808 On The North Side of Dover

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    I just checked out Jefa Tech.
    https://www.jefatech.com/collections/raw-cable-by-the-foot
    They have the best price on 400 style coax I have seen. The price on the 600 is low enough that it becomes a great replacement for 400. They are right next door in Maryland too.Thanks for the heads up!
     
    hotrod likes this.
  15. dave457

    dave457 Well-Known Member

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    Air802 has some good prices as well
     
    ShadeTreeMechanic likes this.

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