Ladder Line Page 4

Copyright © 2002, 2006 by Harold Melton, KV5R. All Rights Reserved.

Entry: Feed-Throughs and Lightening Arrestors

How to make your own spark-gap shunt (“lightning impulse arrestor”), waterproof ladder-line feed-through, and quick-disconnect for (hopefully) improved lightning safety, using common hardware. Or, how to possibly avoid the “billion-amp arc in the shack” scenario.

Disclaimer: All disclaimers apply. No guarantees. I am not an engineer nor expert in the field of lightening protection. I assume absolutely no liability for your use of this material. These ideas have not been tested. Use at your own risk! The actual effectiveness of these measures cannot be quantified. Lightning is dangerous, destructive, deadly, and unpredictable, due to rapid release of incredible power, and extremely wide range of variability.

My HF antenna is a 160 meter dipole, fed with 14-gauge windowed ladder-line. This arrangement should make a nice lightning collector, so I took special precautions on the entry path of the ladder-line.

In figure 1, notice the PVC standoff (one of two), made of half-inch PVC, about six inches long, attached to the trailer with aluminum angle. The ladder-line proceeds down to the arc-shunt assembly, which is mounted directly on the ground rod. It then proceeds up to brass feed-through assemblies (Fig. 2). Once inside, it plugs into the tuner with banana jacks (Fig. 3), for quick disconnection.

The ladder-line is kept separate from all the other cables, which enter via a 1½-inch PVC nipple and coupling (inside) through the floor. The coupling is packed with paper towels (and a little boric acid powder) to keep out bugs. The arrangement provides a good seal that can be easily removed and replaced to allow passage of PL-259s intact.

Continued…

7 thoughts on “Ladder Line Page 4
  1. Can I use a commercial lightning arrestor made for coax? The equipment side of the arrestor will have a short coax jumper to my tuner. The antenna/ladder line side of the arrestor will have a balun to match both sides. Sounds good on paper, but wanted you suggestion on the matter. The arrestor is rated for HF frequencies.
    Learning a lot from this blog, especially about NVIS theory.

    • Yes, Radio > coax > tuner > coax > arrester > coax > balun > ladder-line > balanced symmetrical dipole, is a very good plan.

      Or, if you use tuner’s internal balun, put arrester between radio and tuner.

      Always disconnect at radio during thunder, regardless of type of lightning arrester they are not surge suppressors!

      Optimally, short (a few feet) of RG-8 or -213 coax jumpers; arrestor of the gas-tube type, balun of the dual-toroid-cores current type, ladder-line of the #14 stranded type.

      Best place for outdoor balun is under eave; best place for arrester is mounted directly on ground-rod clamp.

      Waterproof outdoor coax connections with a layer of Scotch 33+, then Coax-Seal (or Scotch 130C), then another layer of Scotch 33+. Never put Coax-Seal directly on coax connectors, or you’ll never get it off!

      Terminate ladder-line to balun with soldered ring lugs, then coat with grease. Nice n tidy.

      73, —kv5r

  2. Lester, got your eQSL card. Thank you.
    Nice web site! I bookmarked it and will reference it for antenna and microscope info.
    73

  3. What about ladder line with an Off Center Fed (OCF) antenna? Doesn’t this cause the ladder line to radiate? How do you deal with this?

    73 K6CUI

    • Yes, ladder line on an OCF will radiate, since the parallel conductors will not be 180° out of phase. Ladder line needs a balanced load to work properly as a feed-line. I wouldn’t use it on an OCF — although some do, when they want the feed-line to be part of the antenna, and can tolerate some RF in the shack.
      73, kv5r

  4. What effect will trees and leaves have on 600 ohm ladder line?? I plan on installing some on a new doublet for 160-10m and it will be next to impossible to run the feed totally in the clear. Please email offline!

    Thnx.

    Philip KA4KOE

    • Shouldn’t be a problem if you use insulated wire for the ladder-line. Some inductive losses may be from running line less than a few inches from conductors (tree branches); probably not enough to notice.
      Make sure to provide physical slack for wind-storm tree flop — a bungee or nylon-line-pulley-weight at one end..
      73, –kv5r

Leave a Reply

Your email address will not be published. Required fields are marked *