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Slinky Doublet

Discussion in 'Amateur Radio Antennas' started by HomerBB, Feb 21, 2021.

  1. HomerBB

    HomerBB Sr. Member

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    With so much talk about HOA/wife antenna restrictions I decided months ago to experiment again with an attic antenna. I didn't, until now. Because of the weather lately with my feedline buried in snow drifts my main end fed multiband HF wire antenna had become unreliable. I don’t do outdoor antenna repairs in temperatures under 20°.
    I ordered some slinking. I failed to look closely at my order and I purchased the 2" diameter slinking instead of the original 3.5". Oh, well. So I strung up a cord in my attic near the peak of its greatest length, about 40' long. I put a two slinkies on the rope, one for each side of a center fed dipole, and stretched them out to ~11' each. To the ends of each of the slinkies I added another 21' of wire.
    I now had a dipole that measured 32' on each side, or 64' total. The dipole is fed with a 10' section of 1' wide twinlead, and then a 10' length of coax down to the tuner ( I will be replacing the whole feedline with 450 Ohm to my other tuner, a balanced unit).
    It will tune from 80m to 10m as it is.
    The most difficult band to tune is, oddly, 20m.
    I get ~1.8:1 SWR there. Everywhere else is ≤1.5:1 SWR.
    It has great ears. And the only contact I have had time to make was given a 56, while I received at 58. That was on 20m only 1100 miles away.
    More later as I refine the components and feedline, etc.


     
    NZ8N and GA1dad like this.

  2. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    The Old Slinky set-up been around for years Homer.
    Most likely when you change to Ladder Line the tuning will all change.
    Once the feedline change occurs sweep it with your analyzer, see where it fall's in at.
    You might find adding/removing a couple feet of stub it will fall in difference locations.
    (I would bet on it!)
    My 8JK array (Phased Doublet) antenna started out at 135 ft overall (each dipole)...
    I played with the tuning and settled for 124 feet overall.
    This gave me: 200 Ohm impendence(Z=200) with ZERO reactance (X=0) from about 3.820 thru about 3.900(y):LOL:
    So just depends on where you want to optimize your usage.
    Hope all is well
    All the Best
    Gary
     
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  3. HomerBB

    HomerBB Sr. Member

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    Thanks, Gary.
    I can do outdoors, but was wanting to play.
     
    BJ radionut likes this.
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    LOL Reminds me of the time I was at the top of my tower fixing a stupid mistake made a few weeks earlier. Somehow I had forgotten to tighten the rotator bolts and the antennas were windmilling. It was a nice sunny and fine day, but the temperature was around -14C or about 7F. At some point I had a complete loss of brain function and placed a stainless steel bolt in my lips to hold it for a second. Which they did. Even after opening my mouth to release it. Yup, instant frostbite on my lips. Lesson learned.
     
  5. HomerBB

    HomerBB Sr. Member

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    And now you know. The normal rules don't apply in cold weather.
     
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  6. HomerBB

    HomerBB Sr. Member

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    A little more info...
    At a distance of about 20' in each direction (north and south) from the center feedpoint my doublet runs into the gables of my main roof in the attic. What I've done is bend the wires at right angles, one toward the east, the other toward the west, following the roofline to finish their lengths.
    I have been contemplating adding another "tail" of wire at the point where the right angle turns are made. This would form an inverted V at the gables like a kind of capacity hat. I am curious whether the combination of the slinky inductors and the end hats I might increase the usable bandwidth and perhaps capture some of 160m.
    Google photo below shows my roof ridge I'm working under. Screenshot_20210221-201242_Maps-01.jpeg
     
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  7. Beetle

    Beetle Sr. Member

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    Be sure the Slinky you use is metal. The plastic ones don't work nearly as well.
     
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  8. HomerBB

    HomerBB Sr. Member

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    No doubt!
     
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