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600 ohm open wire (ladderline) construction

Discussion in 'General Technical Questions and Answers' started by VA3GRV, Oct 5, 2006.

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  1. VA3GRV

    VA3GRV Ham Member QRZ Page

    Hi Folks,

    I'm looking for plans to build my own ladderline, can anyone steer me in the right direction? Can't seem to find any plans online. Also how to run it into my shack.

    Thankyou
    73 Vince
     
  2. AG3Y

    AG3Y Ham Member QRZ Page

    Virtually any ARRL Antenna Handbook that I can remember ever seeing, has instructions for building open wire feeder. There are charts for wire gauge, spacing, and hints on choosing insulator material, ranging from wax-soaked dowel rods to plastic clothes-hanger rods.

    You shouldn't have too much trouble finding the book, which is available at almost any hamfest. Or do what I just did recently, and pick up a copy at a used book store in your area.

    Good luck ! 73, Jim
     
  3. VA3GRV

    VA3GRV Ham Member QRZ Page

    Thankyou Jim, Guess I'm being lazy hihi, Thought for sure I would have found something on the web. Maybe I'll have to order a book.
     
  4. W5DXP

    W5DXP Ham Member QRZ Page

    It's certainly not rocket science. W7FG uses normal #16 insulated wire and makes the spacers out of half inch irrigation tubing available at Home Depot or Lowes. Spacers are about three inches long with notches in each end for the wires. Piece of cake.
     
  5. AG3Y

    AG3Y Ham Member QRZ Page

    I've seen ladder line with the spacers threaded on the wire, but the easier way to do it is to make the knotches as Cecil suggests, and then use small pieces of bus wire to fasten the line in the notches. The bus wire has negligible effect on the characteristics of the feedline.

    Remember that it is really not all that important to match the antenna impedance to the feedline impedance when working with this setup, unless you are actually trying to transform one impedance to another using the line as a quarter wave matching device. Most instances I know of, that is not the case. One of the very first installations I ever saw used open wire feedline spaced about 4 inches apart, and the setup worked like gangbusters! I seriously doubt that the fellow actually had any idea of what the feeline impedance actually was !

    I'm using some commercial ladder line here, but the only "design" consideration that I used was to make sure I had enough line to go from the feedpoint of my antenna to the balun just outside the wall that I feed a short piece of coax through. Real scientific approach for this "Extra-Class Snob", but I certainly make as many contacts as I care to with the setup, so as the old saying goes, "if it works, don't knock it! "

    [​IMG] [​IMG] [​IMG]
     
  6. VA3GRV

    VA3GRV Ham Member QRZ Page

    Ok Thanks Guys....I thought there was a formula for the spacing.I thought I would try it, my current inverted V works good but I thought maybe I could improve by running some 600 ohm right to the tuner that has posts for open wire, rather than using the 31 ft. of 300ohm ladderline with a coax balun then to the tuner. The ant. seems pretty good I had a qso with Trinidad on 20m last night! Thought that was Cool!
     
  7. AG3Y

    AG3Y Ham Member QRZ Page

    Oh, there is a formula for the spacing, but that, and the wire gauge all work together to determine the actual impedance. As I said, there are charts in the ARRL antenna handbook, but the actual impedance is a fairly minor consideration as the losses due to an impedance mismatch are very minor for open wire feedline, as compared to the same type of losses for coax cable. The stuff is wonderful to work with. The only thing you really need to watch out for is to keep it a reasonable distance away from other metal. For instance, don't tape the stuff to your tower, or run it along a downspout or the gutters! Stay away from aluminum siding, and you should be OK . [​IMG]

    73, Jim
     
  8. VK4XJB

    VK4XJB Ham Member QRZ Page

    Z = 276 * log(2 * S / d)

    S is the centre to centre spacing of the wires
    d is the diameter of the wire

    S and d are in the same units.
     
  9. N9FE

    N9FE Ham Member QRZ Page

    wa3grv, if you can run your open wire right to the tuner that's the best, a balun right outside the house like ag3y did work's well to, you can also run two piece's of 'i beleve" 75 ohm coax to get you out of the house, as long as your open wire is not laying on metal, you'll be ok, i kept mine a foot off the tower with pvc standoff's, i also run right to the back of the tuner, and use the balun in the tuner, you might have to add or subtract some feedline length to work all band's,, welcome to the world of open wire, this next summer a couple of us are going to experiment with open wire for uhf and vhf, i went from s9 to 20 over to everyone, even the long hauls, mark
     
  10. WD8PTB

    WD8PTB QRZ Member

    Yes there is a formula but in most cases low loss is what is desired so the actual impedence is not critical. I have seen various spacing ,ussualy with #12 or 14 electrical wire, ussualy hooked up to a balanced output of a tuner. Don WD8PTB
     
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