You can build your own multi-purpose balanced line antenna feed point support in just a few minutes using readily available “off-the-shelf” parts. Balanced line transmission lines should be securely attached at antenna feed points to prevent breakage due to “wire fatigue” caused by the flexing effects of wind and the weight of ice loading.
The most common types of balanced line used as antenna transmission lines are show below.
The balanced line antenna feed point support discussed in this article consists of two parts. The top part is a modified plastic dog bone insulator. The bottom part is a “sandwich” type clamp made of durable lightweight weather resistant material. The clamp is attached to the modified dog bone insulator with a stout plastic zip tie.
You can make the top part of the support by drilling a hole (slightly larger than 3/16” diameter) through the center of a plastic dog bone insulator. The next step is to insert a 3/16” diameter stainless steel eyebolt through the hole and secure it with a stop nut. It’s a good idea to use flat stainless steel washers on either side to bridge the ridges in the insulator.
The bottom part “sandwich” clamp can be made from weather resistant lightweight composite material such as 3 1/2” wide rigid landscape edging available in 20’ rolls. Other materials such as Plexiglas can be used to make the clamp. It turns out that a single clamp can be made by cutting a 9” long piece of edging and ripping it exactly in half (1 3/4” wide). If you go with the edging, be sure to use a bi-metal or ceramic saw blade because of the abrasive properties of the material. Also be sure to wear eye protection and a mask when cutting the edging.
rigid landscape edging
The next step in constructing the bottom part is to drill holes for the nylon bolts that will secure the two halves of the clamp and cut two threading slots. Since we want the clamp to work with any of the three types of balanced line discussed above, hole/slot placement is important. Drill an appropriately sized hole at the top of the clamp for the zip tie that will secure the clamp to the modified dog bone insulator. Lay a section of each type of window/ladder line on the clamp and mark the spots (centered) where the top edge of the line will catch a nylon bolt. Drill two holes at the spots slightly larger than the diameter of a 10/24 nylon bolt. Drill two additional holes (same diameter) near the bottom of the clamp. These two holes and the hole (second from top) will accommodate the three nylon bolts needed for configuration #1 shown below. Lay a section of TV/FM twin lead on the top half of the clamp and mark the spots where the slots will be cut. Use a drill and appropriately sized bit to cut the two slots. Allow enough spacing between the slots so the TV/FM twin lead is not bent up at a sharp angle as it passes through the slots.
Configuration #1 (300 ohm TV/FM twin lead)
300 ohm TV/FM twin lead
Thread the TV/FM twin lead through the slots and tighten the clamp using three nylon bolts and wing nuts.
Configuration #2 (300 ohm & 450 ohm window/ladder line)
300 ohm window/ladder line
450 ohm window/ladder line
The window/ladder line is placed in the clamp so the two nylon bolts catch the top edges of the gaps in the line.
Tighten the wing nuts to secure the window/ladder line snugly between the two halves of the clamp.
Hanging the support
To hang the support, secure the clamp to the top part (modified dog bone insulator) with an appropriately sized plastic zip tie. The ends of the wire radiators are inserted through the ends of the dog bone insulator and appropriately secured. To connect the antenna, strip the ends of the transmission line and the ends of the wire radiators, and join the corresponding ends of the transmission line to the radiators. Be sure to provide enough slack in the connections so the strain on the transmission line is at the zip tie junction and not on the wire ends.
zip tie used to secure clamp to modified dog bone insulator
(1) Keep a spare balanced line support handy as a template for future use. You will be able to lay the template over the material to be used and mark the spots for the holes and slots.
(2) To lower visibility of the finished antenna, use black THNN coated wire for the radiators, black dog bone insulators, black zip ties, and spray paint the bright metal, nylon bolts/wing nuts and clamps with camouflage dull black paint.
It won’t take you very long to make several of these supports so you will be ready for future antenna projects.