Bob's Shop Notes:
Cockpit Port to Comm Antenna
for Hand-Held Radios . . .

You can make the coax between cabin connector and antenna several feet too long and terminate the end with a BNC cable male connector. Use a bulkhead female connector to terminate the coax that continues on to the transceiver. If the panel mounted equipment is down for any reason, you disconnect the antenna coax from the bulkhead female and extend the extra length to the hand-held.

A number of folk have indicated an interest in a sexier solution . . . more expensive too. Several suppliers offer a "coupler" that houses nothing more than a closed circuit headset jack and a couple of connectors. A relatively simple box but with prices ranging from 50-150 dollars.

In the adjacent photo, you see less than $5 worth of parts used to accomplish the same task with about 30 minutes work on the bench. I started with two strips of .010" brass shim stock, 3/4" by 2.25". Mark off length in thirds and drill two .175" holes in one end panel, and one .250" hole in the other end panel. Bend at the marks to make a "U' chassis for mounting a Radio Shack 274-248 jack.

Prepare the ends of your coax feeders so as to bare approx .25" outer braid, 1/8" inner insulation and 1/8" center conductor. Stick ends of coax through small holes and solder to brass. Cut two .5" pieces of 22AWG wire and use as jumpers between stubs of coax center conductors and solder terminals on the jack. These jumpers are used to keep the stiff coax conductor from putting stress on the relatively fragile jack terminals.

Next . . . .

When you get all done, you'll have a 3/4" hollow cube of brass that houses a miniature, closed circuit headset jack with enough threads left on its mounting bushing to come through a 0.62" panel or bracket and accept the jack's mounting nut. The thin stock is a little flimsy to work with but once the cube is all closed up, it becomes quite rigid. Since the coupler mounts by a single threaded fastener (the bushing of the phone jack) you'll want to support the two feedlines a short distance behind the coupler when it's mounted so that the wire weight will neither flex nor twist the coupler's housing. You can do the same thing with a larger, 1/4" phone jack and make the enclosure a bit larger.

I prefer this technique for several reasons. It's inexpensive. It's compact. It minimizes the number of connectors in your radio's antenna feedline . . . and last, it's easy to do.

I'm pretty much down on older coax products like RG-58 (and the miniature cousin RG-174) for use in the airframe wiring, they use polyethylene and polyvinyl chloride plastics. HOWEVER . . . to minimize stress on your hand held's antenna connector -AND- to make handling of the radio easier in the cockpit, these legacy materials are more user friendly than RG-400. Consider fabricating your hand-held-to-coupler jumper from either of these cables.

I use RG-400 with my hand held and to make it more cockpit friendly, I use a pair of right-angle BNC adapters to turn the hand-held's antenna routing so that it runs down along the back side of the radio. This makes the relatively stiff RG-400 lay nicely along the radio's "spine" and exit out the bottom - much nicer to use than to have a large loop of coax waving around in the air above the radio. The same technique could be applied to the short coax jumper used with this coupler. One could use a right-angle BNC cable-male on the jumper and you would then need only one BNC right angle adapter . . . this would eliminate one set of joints in the feedline.

Fly comfortably . . .

'lectric Bob . . .