Wire Antennas and PVC hanging components: Don't

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD0KZE, Mar 1, 2018.

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  1. KD0KZE

    KD0KZE Ham Member QRZ Page

    I was proud last summer to raise a G5RV between two trees with a loop system I designed using ~3" diameter PVC adapters. These were tied to loops of paracord and could be raised/lowered independently in either tree. I ran the G5RV ends through both, which were wide enough to accommodate the end insulators, and then tied off the G5RV itself to each tree. It involved some extra cord, but with that setup I could raise/lower either end of the antenna like a flag pole, and the antenna paracord wouldn't rub against branches.

    However, we've had some heavy winds and winter storms lately, and within 6 months one end came crashing down. Upon inspection, I see that the paracord (through push/pull action) wore a groove into the edge of the PVC piece -- and the edge of the groove became sharp enough to cut the paracord.

    I've tried pulleys, and hate them -- they can twist or the cord can jump and get caught. Tried metal hitching-post style loops installed by a tree service with a crane. These worked fine until one of the trees lost a good number of large branches and the antenna came crashing down. Didn't want to hire the big crane again.

    So now I've gone back to old-fashioned simple paracord over a branch, tied off with sufficient slack to lower it if needed.

    73, KD0KZE / Paul
     
  2. K1IGS

    K1IGS Ham Member QRZ Page

    That's how my G5RV is hung - paracord over branches. Hopefully it withstands tomorrow's coastal storm.
     
  3. SM0XHJ

    SM0XHJ Ham Member QRZ Page

    Sorry to hear, but yeah, PVC isn't the best material for this. Quite high friction and low wear resistance :-(
    Dyneema without sheath + nylon might be a better combination. But it will wear down over time too.

    Was that marine grade pulleys with swivel? The swivel should prevent the line to get twisted. The line should not get caught if a correctly sized, good quality, pulley is used.
     
  4. KF5FEI

    KF5FEI Ham Member QRZ Page

    The problem with paracord and pulleys is the paracord can flatten out and get hung up. I had great luck with hardware store pulleys and braided dacron rope. It seems to last 10-15 years. I switched to lawnmower pull-cord rope this time, as it seems to be more sturdy.
     
  5. KD0KZE

    KD0KZE Ham Member QRZ Page

    I've tried both marine grade and nylon clothing pulleys. The swivel action drove me nuts, since it would swivel around while raising the pulley itself. I had to manipulate three cords -- the two ends of the loop that raised the pulley over a branch, and the end for the G5RV cord looped through the pulley. Three twisted cords, one angry ham.

    Also, my tree anchor points are closer to 90' than the full distance of a G5RV, so some slack (including the insulator) needs to come over a branch. The pulley can't accommodate an insulator or knots.

    One thing I have learned from this experience, though, is that I swear by the ChuckIt! tennis ball thrower for dogs. I duct taped some kite string to it, reeled out alot of slack onto the snow in my yard, and got it over the branch I wanted within 2-3 tries. Unfortunately, I've had some practice lately.

    73, KD0KZE / Paul
     
  6. SM0XHJ

    SM0XHJ Ham Member QRZ Page

    Ah, yes, that complicates it. I have a very similar problem with the 80 meter section of my fan dipole. Haven't figured out a good solution to it yet. First I had it simply thrown (or rather shot, I use bow and arrow) over the tree limbs, as you have. But the antenna wire ate into the bark (or the bark grew into the wire) and the wire got stuck. Then some wind and the wire snapped.

    I have been planning to splice in the antenna wire with a Dyneema rope like this:
    http://www.foghmarine.com/assets/images/rigging/Splice-Wire-to-Rope.jpg
    But even though Dyneema is know to absorb very little water, I'm concerned it will still be problematic when wet or icy.
     
  7. NH7RO

    NH7RO Ham Member QRZ Page

    Me, too. I recently threw a couple of lines up into some oak trees for a couple of H-double bays I built for 6M using a ChuckIt. Instead of the included neon orange tennis ball I used a hefty 2-inch steel hex nut that I tied my line to; It launched almost as good as the Space Shuttle!

    I also discovered a neat trick with this, too---since the woods I was in are full of thorny vines and twigs that love to catch or snag lines---I loosely stuffed about 60 feet of thin Dacron line into a wide-mouth plastic jar (about 4" x 9") before launch. Holding the jar of line in one hand and launching the hex nut via the ChuckIt in the other was super easy and effective; despite the many twisted branches and thick canopy I managed to place both lines after three or four tries first time out.

    I am retiring my slingshot in favor of the ChuckIt!

    73,

    Jeff
     
  8. KD0KZE

    KD0KZE Ham Member QRZ Page

    Thanks, I like the jar idea alot. The trouble with my kite string method is that I had to unspool 30-40' of slack before launching the ball. It slows down enough at apogee such that I can release additional slack manually with the spool in my non-throwing hand. But white string over a yard covered in 1-2 feet of snow became an invisible and tangled mess. I had to free myself a couple times.

    Over the summer I drove a stake into the ground, and clamped a rotating reel of string to it, so it would freely unwind as the projectile went up. Not possible in the winter, since the ground is rock-solid. A jar of dark or vividly colored thin Dacron would be winter-friendly.

    I don't like slingshot or bow/arrow methods due to my smallish lot, and potential for "collateral damage". These ChuckIt's seem pretty ideal for hitting 30-40'+ heights. Paleolithic solution (atlatl) to a modern problem.

    73, KD0KZE / Paul
     
    NH7RO likes this.
  9. NH7RO

    NH7RO Ham Member QRZ Page

    Yeah, Paul; I know exactly what you mean about unspooling line in advance of launch and I was actually quite surprised that my open jar method worked perfectly---not the slightest bit of snagging or tangling---the line just vanished as soon as I "chucked it." I am now thinking of looking for more trees to toss other lines over for a stealthy fan dipole or two it was so easy the first two times.

    Btw, I'm also glad I attached a smaller weight to the end of the line that was stuffed into the big plastic jar; the entire 60 or more feet that I used shot into the air during launch and if I hadn't had the foresight to put another weight on the far end I might have lost it in the trees.

    Sometime I'll post a picture of my trusty ChuckIt (painted camo green for stealth) and big plastic jar I used to help others launch antenna lines in confined spaces like mine.

    73,


    Jeff
     
  10. WA7F

    WA7F Premium Subscriber QRZ Page

    I use a pulley and counterweight on every wire antenna. It keeps the wire reasonably tight even when the trees are blowing. The counter weight just bobs up and down while they trees sway. You do need to use some caution to avoid twisting while pulling it up but, it never been a problem once it's up. I use decent pulleys, no Harbor Freight junk. Usually steel or SS but, a big clothes line pulley from Home Depot is light stronger than you might think.

    I have a 13 gauge copper over steel 600 ohm ladder line feed 80 meter dublet at (260' horizontal plus 90' of ladder) and a 130' Inv-L (same wire type and size) hanging from the same rope between two trees. I shot the ropes over branches at 100 to 115' and it's over 300' between the trees. Its a longer run than I would have prefered but, you work with what you have. I use a 40 pound counterweight but, it work Ok with 25 pounds if you don't mind some sag. Everything is is rated at 300 pound test or higher.

    Anyway, PVC is poor choice in my opinion. If you have no other option at least use the grey UV stabilized conduit or paint it. A clevis or one of the removable chain type links will avoid chaffing at the rope connections. I only use Stainless Steel hardware anywhere near the RF. The intentional weak link in the system is the clothesline pulley at the apex of the Inv-L. If it were to break at that point it's an easy fix.
     

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