Long Wire Antennas - In the trees?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W9KEY, Sep 27, 2018.

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  1. W9KEY

    W9KEY XML Subscriber QRZ Page

    Am giving thought to putting up a long wire loop antenna. A rough pace-off of the backyard seems to provide suitable tree locations allowing for about 540 feet of wire - not as much as I'd hoped for. More study is required. Existing trees are randomly located, so the enclosed loop area will have an uncontrolled irregular shape.

    But here's my (probably) dumb question. If using common, solid, home electrical wire (#14 or #12, which I have a good supply of), is it OK to run the insulated wire directly through the trees, over branches and touching leaves? Running through (or better yet - around the outside of) the trees will allow for a longer wire run, versus suspending the wire on insulators away from the tree canopy. But will that cause impedance problems when it rains, or when the tree bark eventually rubs through the wire insulation, or with propagation nulls due to limbs only a few millimeters away from the copper?

    Was hoping to use something like this for 160 meters, but probably not long enough to do anything except shoot straight up. I'll probably be lucky to get it much above 40 feet, especially with the droop in longer spans. I already have a multi element dipole for 80-10 m, but it's only about 25' high.
     
  2. G3YRO

    G3YRO Ham Member QRZ Page

    Even having any part of an antenna within a few feet of trees will de-tune it, and cause absorbtion of radiated power.

    Actually running over branches will be FAR worse . . . whether you use insulated wire or not!

    Can't you use insulating halyards, so that you keep the wire away from the branches?

    Roger G3YRO
     
  3. WG8Z

    WG8Z Ham Member QRZ Page

    Go for it. Don't worry about the leaves.
    Slide a bunch of sections of vacuum line hose on that you can locate where it contacts tree branches and/or tie off with halyards.
    Feed it with 450^ windowline to a good tuner balun or directly to a balanced tuner.
    Been there, done that. Will be a good ragchew antenna for 160m out to about 300-400 miles.
     
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  4. WG8Z

    WG8Z Ham Member QRZ Page

    FWIW Stranded insulated would work better. Easier to deploy and more resistant to flex fatigue. Think THHN
     
  5. KD6RF

    KD6RF Ham Member QRZ Page

    If running high power, I'd be a bit concerned about arcing. Absorption will be an issue, but almost certainly not a huge one. Height usually trumps a bit of additional loss.

    The big issue with running wire directly over limbs is abrasion and bind - it won't take long for wind and sway to wear through insulation. After that, who knows - wire will abrade and/or will eat it's way into the limb and bind up. Neither is good. At minimum, the hose sections mentioned above are a good idea - free-moving pulleys and suspension ropes are better.


    Not part of your question, but putting a bunch of wire in the air doesn't always correlate with putting out a good signal to where you want it to go. For example, a low strung horizontal wire is going to be a cloud/burner / NVIS antenna on the low bands - regardless of whether it is 100 feet or 1000 feet of low-strung wire. You can make DX contacts, but not as easily as with a good vertically polarized antenna.

    Of course, that's fine if local-ish comms is what you're after. If you are more interested in low-angle DX, then other antenna types would be more likely to give you a good result - usually vertical polarization.
     
  6. AA7EJ

    AA7EJ Ham Member QRZ Page

    Big loop like that, irregardless of proximity of trees, radiation pattern is like the "box of candy" - you never know what you gone get.
    Use whatever wire you have handy. I used about 600 ft of telephone drop wire - copper clad steel.

    Be aware you are building a temporary antenna.
    Or long term maintenance headache.

    Squirrels love insulation , hence proximity to trees is "easy picki'n " for them.

    Best of luck AKA 73's
    Shirley
     
  7. AI3V

    AI3V Ham Member QRZ Page

    I use exactly the same setup when camping.

    Try not to touch trees with the wire.

    You will " get out" just fine.

    If you are interested in a specific direction, read up on "vee beams" and "rhombic" antennas, and try and get a corner pointed that way.


    Rege
     
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  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    A 540' loop should work on 160m and all harmonics of 160m, but the "harmonic relationship" works out a bit funny, as wherever it's resonant on 160 it will usually be resonant a bit higher in frequency than the mathematical second harmonic, and a bit higher in frequency than that on the third harmonic, and so forth.

    But a good tuner makes up for all that.

    At 40' AGL it's certainly a "cloud warmer" on 160m and 80m, but can start to perform really well on 40m. Peaks will have some gain, nulls will have some loss, but overall not a bad solution.

    The issue with running through branches and leaves is the "fire hazard," to me. At QRP levels, zero problem. At 100W, probably not a problem, usually. At a kilowatt, can be a real problem. Most household electrical wire has insulation rated 300Vrms. With "power," there are parts of a loop that will have a greater voltage than that. I've set trees on fire a couple of times with wire antennas, even "insulated" ones. Heavy insulation helps, and Teflon insulation can be fairly thin and still work; but the standard PE or PVC insulation found on conventional electrical wire isn't great -- it's also not really rated for outdoor work, which is why NEC requires outdoor wiring be in conduit and not exposed.

    Here's a counterintuitive thing: I set a tree ablaze running a kW on 80m with a wire antenna -- in a rainstorm. Electrical arcing is not considerate of stuff being wet.:p
     
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  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    THHN (Thermoplastic High Heat-resistant Nylon) describes the insulation, and has zero to do with the wire itself. From http://en.wikipedia.org/wiki/Electrical_wiring_in_North_America#Wire_types:
    "Wire with THWN or THHN insulation is commonly used in the AC electrical distribution systems throughout North America, usually at voltage levels from 110 to 600 volts. This type of insulation is used for both copper and aluminum conductors which are either solid or stranded, depending on size."

    Further, when stranded, it is typically only 7 strands. More strands increases flexibility. The wire is soft-drawn and, when used as an antenna, will stretch. I use only wire w/ LOTS of strands that is hard-drawn. Davis RF (http://www.davisrf.com/) and others sell it. Others like CopperWeld, and they sell that too.
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I like lots of strands, too, as long as the wire is insulated.

    Bare (uninsulated) wire with a lot of strands is subject to easier breakage from abrasion.

    I use mostly 168-strand copper, insulated wire.
     

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