Hardline

Homebrewing connectors for 7/8-inch Prodelin feedline

Paint-removal wheel on drill makes quick work of removing outer sheathing to expose aluminum jacket.
Paint-removal wheel on drill makes quick work of removing outer sheathing to expose aluminum jacket. Wear eye protection!

Prodelin and other hardline often can be found on the surplus market but connectors may be expensive or unavailable. These offer the advantage of much lower loss than coax and extreme physical durability.

I acquired a large amount of 7/8-inch 50-ohm Prodelin some years ago and have devised a number of means for making connections.

The simplest hardline splice uses just one hose clamp for the shields, a wire jumper for the center conductors and an old soda bottle for weather protection.
The simplest hardline splice uses just one hose clamp for the shields, a wire jumper for the center conductors and an old soda bottle for weather protection.

Some of the simplest connections I’ve used have been bare-bones, with an all-stainless hose clamp bonding the hardline shields, and another hose clamp on the center conductors, or solder a short wire between the center conductors. A cut-off soda bottle is placed over this for weather protection (thanks VE1ZZ for that idea!). Similar method can be used to join a piece of coax and hardline.

Another method for the center conductor is to drill a 1/8 inch hole in the hardline center conductor, and use a brass or stainless steel 6/32 bolt with washers to connect a wire to the hardline. A 1/4 inch sheet metal screw could be used to do this in the shield too.

Electrical feed-through connectors (1-inch size) work well on this Prodelin when it terminates in any of a number of small metal boxes I’ve used for shielded terminations or switch boxes.

Another type of hardline frequently available is surplus CATV 75-ohm, in 3/4 inch or half-inch sizes, and some others. Before acquiring the Prodelin, I used much of this without worrying about the slight mismatch (1.4:1 SWR) with 50-ohm antennas, taking advantage of the lower loss vs. coax cable.

Prodelin 7/8 inch hardline enters homebrew switching box outside hamshack.
Prodelin 7/8 inch hardline enters homebrew switching box outside hamshack.

PL-259 connectors can easily be mated to the 1/2 inch hardline with a small piece of aluminum “sleeve” and one or two small hose clamps.

With 3/4 inch ┬áCATV hardline, a double-barrel SO-239 connector (PL-258) can be inserted in the end of the hardline — it is a perfect fit after removing a half-inch of foam dialectric and slitting the shield. A single hose clamp keeps it together.

Copper, brass and bronze plumbing fittings also can be used to make nice and neat connections to hardline, in combination with PL-258 connectors.

 

Electrical feed-through connectors make an easy clamp for hardline connection. Replace bolts with stainless.
Electrical feed-through connectors make an easy clamp for hardline connection. Replace bolts with stainless.

 

 

Homebrew relay box under construction, built in military test equipment surplus box.
Homebrew relay box under construction, built in military test equipment surplus box.
W3PP (SK) devised this connector using plumbing fittings to step-down 7/8-inch Prodelin to a PL-258 barrel connector.
W3PP (SK) devised this connector using plumbing fittings to step-down 7/8-inch Prodelin to a PL-258 barrel connector.

 

CATV hardline 3_4_inch to PL-258 connector