BALANCED FEED LINE – ROLLING YOUR OWN - （平衡饲料线-滚自己的）.pdf

BALANCED FEED LINE – ROLLING YOUR OWN by VE1VQ Some years ago, I had the pleasure of visiting Seab, AA1MY, when he lived in Connecticut, and seeing his 1500 foot horizontal loop and his homebrew feed line made with “whipper-snipper” plastic line as spacers. He demonstrated how he made the line using a soldering iron to form the end loops to hold the two wires. When I first considered making my own feed line to replace the old commercial twin lead with vinyl in the center, and showing its age, I gave some thought to Seab’s method, but abandoned it when I looked at the cost of the trimmer line around here. My recent ARRL Handbook gave me the formula for spacing and impedance, as did the ARRL Antenna Book (15th edition), but not much in the way of practical stuff that I could use. One of my computer friends says, “Google knows all”. That might be, but Google didn’t seem to know much about balanced line for RF transmission! One of the few places where I found any real information was that of L.B. Cebik, W4RNL. His web site has all kinds of good stuff about antennas, tuners and feed lines.1 Others talked about using cut up wooden dowel, plastic pipe or rod, or coat hangers for the spreaders. Some used heat to force the bare wire into the ends of the plastic, others used the more traditional method of drilling holes and wrapping wire, and still others updated this with tie-wraps (although at greater cost). Nowhere could I find an actual process (with pictures) to make balanced transmission line. GETTING READY Since I have a 500 foot horizontal loop antenna varying in height above ground of from 25 – 40 feet, and feed it from a homebrew balanced tuner 2 , I wasn’t all that concerned with the actual impedance of the finished line, as long as it was reasonably high (somewhere between 450 and 600 ohms). I picked up some black plastic hangers (See Fig. 1) from the local Dollar Sto