[TowerTalk] Solid 160 radial plates?
k4kyv at hotmail.com
Tue Aug 28 13:38:49 EDT 2018
> I'm not sure what the metallurgy of the screw and bar would be like in
> conjunction with solder. Of course the bar should be fine with copper
> (and I think even with aluminum in alkaline soil environments), so if I
> was hesitant about screwing down on multiple small wires (a valid
> concern, I think) I'd probably solder the smaller wires to one larger
> one to go into the bar. And of course I'd use lead free solder since
> lead and moisture are bad bedfellows.
> I probably wouldn't bury the bar underground because you never know what
> corrosive effects might be there, but you can screw the connections so
> tight that I'm pretty sure the metal to metal interface approaches that
> of a weld. I don't think having it exposed to the elements above ground
> would be a problem.
I don't understand why you guys waste time, energy and money with those Hammy Hambone radial plates in which the radials are attached with screws. Much easier, cheaper and longer lasting is to lay a copper ring round the base of the tower, and solder/braze the radials to it. The ring can be made of copper tubing, solid #4 awg wire, or strips of sheet copper. This has long been the standard procedure for AM broadcast towers.
Braze the radials to the ring using the same silver solder plumbers use. It comes in sticks about 18" long and 1/8" wide; the alloy is 15% silver, lead free. You need something hotter than an ordinary propane torch; I use MAPP gas, which works just like a propane torch. It must heat the copper to a dark red glow to fully melt the alloy to liquid form. As long as the copper is free of scaly crud, no external flux is needed; the heat burns oxides off the bright copper. The molten solder adheres to hot copper like a sponge soaks water. The connection does not deteriorate over time in contact with in the soil. I built mine in 1983, and the connections to-day are just as solid as the day I put them in, with no signs of corrosion. The same with above ground outdoor feedline and antenna connections.
The silver alloy brazing rods are available at any plumbing supplier. They are not dirt cheap, but not overly expensive either, since plumbers use them for sweating copper pipes. Codes prohibit lead solder for plumbing, so demand is high and supply plentiful. NEVER use ordinary lead solder; it reacts with minerals in the soil and quickly deteriorates and turns into a white powder. I once used lead solder years ago for a radial system and had to routinely re-solder the radials about once a month. That's why lead solder is not used in plumbing; minerals in the water cause the same deterioration of the solder and the connection will eventually leak. Plus, there is concern about lead leaching into the potable water supply.
The only circumstances where "radial plates" MIGHT be a useful solution would be for temporary installations, like a field day setup or experimental antenna. I would never use them for a permanent installation.
More information about the TowerTalk