Hardline Splicing

This page describes how I splice some 1-5/8 inch hardline together. The reason for splicing the LDF7-50A Heliax was because I wished to use connectors for the new-style of Heliax with some old spiral type Heliax since I was unable to find any connectors for the old cable. I bought two Cablewave NF connectors and about 8-feet of new Heliax from Marshall, K5QE. I used a short piece of 1/2-inch copper tubing bought at the local hardware store to connect the center conductor. The Heliax is also 1/2 inch so I slit it at right angles (Fig. 1) so that I could bend the center into a rough cone (Fig. 2). Then the 1-inch long copper tube fit over it. The separation between the two pieces of hardline was about 1.25 inches with the center conductor splice. To avoid causing a large impedance bump I made a couple hemi-circular sections of the outer cable with insulation such that they would clamp over the 1/2-inch copper tube (Fig. 3,4,5,6). I made these from a 1.25 inch slice of cable which I sawed lengthwise. I removed the center conductor and dispose of it and cut out enough of the center insulation to fit over the 1/2-inch copper tube. I held the two half-rounds of cable in place by tying solder around them to hold them (Fig 7). I square piece of thin copper sheet was then formed around the cable overlapping the spliced area. This was clamped with two hose clamps so that it would be held in place for soldering (Fig 8). Soldering was done using a propane torch. Click image to see larger view: The question was whether the splice would preserve the impedance of the coax line and how much loss would exist thru The 120-feet of spliced cable. The impedance was 59 +j0 using a 52-ohm coaxial termination at the far end. This offers a SWR of less than 1.2:1. Cable loss was measured at 144-MHz as 12% (0.56 dB) which is more than new LDF7-50A (spec'd at 0.31 dB loss/100-ft). Probably extra loss due to age of cable and the splices, but better than the 1.25 dB loss of the existing 103-foot run of LDF5-50A 7/8-inch Heliax plus about 20-feet of LMR-400 jumpers for connecting each end. The 1-5/8 inch line connects with about 7-feet of LMR-400 at the shack end. The antenna end directly connects to a 45-foot run of 7/8-inch hardline attached to the eme tower. Roughly 80% of the 144-MHz RF output will reach the top of the eme tower. Return to the Home page.