Open Wire Line

Discussion in 'Amplitude Modulation - AM Fans' started by W2NBC, Sep 8, 2017.

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  1. W2NBC

    W2NBC Ham Member QRZ Page

    I have been using balanced line for years to feed various antenna configurations here at the station. Originally, with lighter power handling requirements, I used the 450 Ohm #14 "window line" which sort of works but at a tremendous cost due to the marginal dielectric and its cross section to conductor ratio. That resulted in tremendous swings in matching because of rain, whipping around in the wind, and even heating in the sun.

    I started to construct and experiment with the construction of open-wire line using various insulators. The BEST (and traditional) of course would be of the ceramic spacer variety, and in a situation where rigid supports (like towers) are used with minimal sway in wind, that would be ideal. The ceramic insulators I used are HEAVY coupled with the weight of the wire itself and can significantly pull on the center support of an antenna. In my case, (using #10 wire) with VERY tall trees used as antenna supports, weight and antenna sway was indeed an issue.

    In researching various workarounds online, 8 years ago or so I discovered this video:

    https://www.youtube.com/watch?v=qzFKGB6qkXs

    Ok, "PENS" ??? Hammy Hambone at it's finest! Interesting.. BUT..

    They are NOT UV resistant! Those pen "insulators" will crumble after one season and look like a play toy your dog Rufus used to CHEW. (just ask THIS Hambone how I know).
    The other and equally important caveat is the type of cable ties used to affix the wire. The run of the mill Home Depot or Lowes Chinese-made variety are rated at "80 Lbs". In truth, the quality and composition of the wraps are suspect. So I did some tie-wrap-research "TWR" online and it seems as though the ONLY way to go isn't for tensile strength but for AMERICAN made UV stabilized "NYLON 6/6, ISO9002 CERTIFIED". What was happening with the Home Depot type was that every other one would break because of the inability to make the severe bends around the wire itself (securing it against the insulator). Flexibility and real UV ratings are KEY here, and US made cable ties are the only way to go.

    The "pen insulator" video IDEA has merits if different insulators and cable ties are used. The trend for replacement insulators has been "Fi Shock Fence insulators" (4" spacing):
    http://www.zarebasystems.com/zareba-4-inch-fin-tube-insulator-ht4fti200

    You will notice that they are 4" spacing, and have what appears to be "ribs" of plastic that could catch snow, water, etc. Here is a great link to constructing open wire utilizing the "Fi Shock" (but with slotted ends and hot glue minus the cable ties):
    http://www.w1aex.com/owl/owl.html

    Several years ago, I decided to use the US made cable tie and fence insulator approach using these:

    http://www.rammfence.com/fence/horse-fencing-accessories/electric-fence-accessories/insulators/5-inch-insulator-tubing

    These are 5" spaced, rigid, UV resistant, and EXCELLENT for open wire insulators! The 5" spacing using #10 wire = characteristic (Zo) 560 ohms. I constructed about 175 FT of open wire using just the cable ties and these insulators. So far, there are absolutely NO signs of degradation of either the cable ties or the insulators. The antenna I am feeding is up at 95 FT and certainly has some sway in the wind.. It seems as though I can expect some good longevity from this feed line!

    Rolling your OWN open wire line is one of the best ways to improve the consistency of any balanced antenna installation.

    I'm interested how you folks have rolled your own!
     
  2. N2EY

    N2EY Ham Member QRZ Page

    I wish I could!

    Here's an idea, though....

    Does anyone know the electrical characteristics of Corian (the countertop stuff?)

    Years ago I got some scraps of white Corian, and the stuff is pretty awesome. Cuts and drills like hardwood but seems to be impervious to rain, ice, UV, etc.

    With basic woodworking tools, one could make spreaders that look like the real thing.

    73 de Jim, N2EY
     
  3. N2DTS

    N2DTS Ham Member QRZ Page

    I have made some in the past using various things.
    The wire ties I used did not hold up long term, nor did the spreaders made of plastic from work.

    For my fan dipole, I went with fiberglass rods and copper wire:
    [​IMG]

    I drill a small hole through the fiberglass rod (reflector holder rods) and use the copper wire to tie on the wire.
    Very light, very strong, should be UV proof.
    The reflector/rods are about $1.00 each and are 3 feet long or more.
     
    N2EY likes this.
  4. W2NBC

    W2NBC Ham Member QRZ Page

    Interesting on the Corian idea! I'm not sure what the UV/dielectric specs are. Also, the fiberglass rods N2DTS used for his fan dipole look promising.

    Here is a pic of the 5" spreaders and cable ties in action ( 3 foot spacing between each) feeding the center of one of my antennas (220 ft center-fed at 95 Ft).
     

    Attached Files:

  5. N2DTS

    N2DTS Ham Member QRZ Page

    Thats high!
     
  6. W2VW

    W2VW Ham Member QRZ Page

    Hi Jeff,

    Looking at the picture makes me ask.

    Is the dipole center insulator being positioned by a rope tied to a third tree?

    That's what it looks like.

    tnx om
     
  7. W2NBC

    W2NBC Ham Member QRZ Page


    Hey Dave,

    Yes, that rope is the center support and is tied to that very tall tree. It also positions the antenna to thread the elements through other trees to keep it high and in the clear. A center support for long dipoles has always worked for me.
     
    N2EY likes this.
  8. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    I've used "window line" for years without any of the problems you seem to have had with it. There's someone selling traditional and hand made ladder line - the link is in the for sale sections somewhere - I just never felt the need for it.

    EDIT: Found the link. Making my own strikes me as very time consuming among the other challenges. If I thought I would see any real improvement over window line I'd just buy some of this:

    http://trueladderline.com/w7fg-design-600-ohm-open-wire-feedline/
     
  9. K4KYV

    K4KYV Subscriber QRZ Page

    I have seen white Delrin rod stock used for spacers. It is physically strong and said to be very good dielectric material. From the ground they look identical to classic white porcelain insulators. I use 2" EF Johnson ceramic spacers in the OWL that runs to the tower, and flat plexiglass strips in the section that runs up through the interior of the tower to the dipole. I use home-made spacers from Plexiglass rods in the OWL that runs from the shack out to the dawg-house at the base of the tower. Plexiglass is said not to be an ideal rf dielectric, but a lot better than PVC. I think it is pretty close to perfect for OWL spacers, since there is so little of it between the conductors in traditional OWL. Pre-WWII, hams in the Great Depression who couldn't afford ceramic spacers, often used wooden dowel rods weatherproofed by boiling in a mixture of beeswax and canning-jar sealing wax.
     
    N2EY likes this.
  10. WA6SW

    WA6SW Ham Member QRZ Page

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