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Alpha Delta DX-B Sloper Mounting

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K4LD, Jun 28, 2020.

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  1. K4LD

    K4LD Ham Member QRZ Page

    Hello everyone,
    I am about to embark on setting up my first sloper antenna for the low bands - An Alpha Delta DX-B. I have a 55’ crank up tower with TH-11DX atop.

    The mounting instructions say to connect a user supplied ‘U’ bolt to the tower on a metal plate that also houses the antenna’s SO-239. Does anyone have a picture of their setup if using a similar mounting method or the same antenna? It’s hard for me to imagine that a ‘U’ bolt will be sufficient enough to provide the metallic support electrical connection as required by the antenna.

    Any other additional tips or suggestions are appreciated. The goal is to make a dent in my DXCC progress on 160M and 80M this coming winter.

    Best regards,
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I've installed those before.

    The metal bracket that contains the SO-239 actually presses hard against the tower leg; the U-bolt goes around the tower leg and its threaded ends go through that bracket.

    If you want to make a better electrical connection, it would be easy to supplement that with some wide aluminum flashing or something; but it probably isn't necessary.

    The problem is that antenna is very heavily loaded and is so short that once "tuned" it only covers about 20 kHz of the 160m band before the VSWR becomes very high. At 50 kHz, it's about 10:1 and at 100 kHz, pretty much infinity. And because the functional BW is so narrow, the installation becomes critical with respect to mounting height, top loading (by the beam, mast, tower above the mounting point, cables, and anything electrically common with the tower) and wire length so it can take a few tries in attempt to get this right.

    The model DX-LB is better; it's still "short" and loaded, but it's center-fed and balanced and isolated from its support, so it's much less finnicky and works better.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    I have concluded that slopers fed against the tower are pretty worthless. You are basically building an inverted-V where one half of the dipole is grounded (at the tower base). The tower has all sorts of unrelated stuff hanging on it. The apex angle of the V is like 30-40 degrees instead of ~120degrees like it should be... At resonance, the feedpoint is far from 50 Ohms... What is there to like????

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