2. Ham Radio

Doublet Reconstruction Photos

I had to rebuild my 88' doublet, here are some photos showing my construction technique. I tossed the original one together with the intent of rebuilding it, never got around to it, and it failed due to insufficient stress relief. Hopefully this one lasts longer.
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I forgot to take a photo of the first step: take a sharp razor blade and carefully remove the insulation along each side of the twinlead for about 3-4" so that you can pull the wires out. Twist each wire so that the strands are together as in a normal stranded wire. Fold the now-wireless insulation back on itself, leaving space at the bend for a little loop on top. <br /> <br /> Put a small zip tie through this not-yet-secured loop and zip it to form another small loop. This loop will be used as an attachment for a support line, and to secure the antenna wires. <br /> <br /> Take two insulated wires that are of identical length (length not critical, my wires were originally 44' long and now a bit shorter after the rebuild), strip about 5/8" from one end of each, and use an overhand knot to tie the stripped end of each wire to the zip tie. Be sure to leave a few inches beyond the knot. The goal is for the beyond-the-knot segments of the wire to not receive any tension, no matter how hard you pull on either of the wires. The wires from the twinlead will wrap around the stripped ends (but not yet). The wire size isn't critical either, I used 24-gauge stranded hookup wire as that is what I had on hand.<br /> <br /> Add a second zip tie to secure the loop in the twinlead. Be sure to run the antenna wires through the zip tie as shown. Cinch the zip tie down tight and trim off the end. <br /> <br /> On each side of the twinlead, twist the twinlead wires around the stripped ends of the antenna wires. Apply solder to the ends of these splices but don't allow solder to flow all the way up to the tops of the splices. The idea is to leave the top flexible, just in case tension ends up being applied to the splice (which should never happen, but best to be safe).<br /> <br /> You'd think (or at least I thought) that a single overhand knot would not be sufficient to keep the wire in place and not slip. However, the "corrugations" on the inside of the zip tie bite into the wires' insulation and hold them in place.I did some destructive pull tests and discovered that the 24-AWG wire will actually break at some other point in the wire before the knot gives way.
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I forgot to take a photo of the first step: take a sharp razor blade and carefully remove the insulation along each side of the twinlead for about 3-4" so that you can pull the wires out. Twist each wire so that the strands are together as in a normal stranded wire. Fold the now-wireless insulation back on itself, leaving space at the bend for a little loop on top.

Put a small zip tie through this not-yet-secured loop and zip it to form another small loop. This loop will be used as an attachment for a support line, and to secure the antenna wires.

Take two insulated wires that are of identical length (length not critical, my wires were originally 44' long and now a bit shorter after the rebuild), strip about 5/8" from one end of each, and use an overhand knot to tie the stripped end of each wire to the zip tie. Be sure to leave a few inches beyond the knot. The goal is for the beyond-the-knot segments of the wire to not receive any tension, no matter how hard you pull on either of the wires. The wires from the twinlead will wrap around the stripped ends (but not yet). The wire size isn't critical either, I used 24-gauge stranded hookup wire as that is what I had on hand.

Add a second zip tie to secure the loop in the twinlead. Be sure to run the antenna wires through the zip tie as shown. Cinch the zip tie down tight and trim off the end.

On each side of the twinlead, twist the twinlead wires around the stripped ends of the antenna wires. Apply solder to the ends of these splices but don't allow solder to flow all the way up to the tops of the splices. The idea is to leave the top flexible, just in case tension ends up being applied to the splice (which should never happen, but best to be safe).

You'd think (or at least I thought) that a single overhand knot would not be sufficient to keep the wire in place and not slip. However, the "corrugations" on the inside of the zip tie bite into the wires' insulation and hold them in place.I did some destructive pull tests and discovered that the 24-AWG wire will actually break at some other point in the wire before the knot gives way.

  • I forgot to take a photo of the first step: take a sharp razor blade and carefully remove the insulation along each side of the twinlead for about 3-4" so that you can pull the wires out. Twist each wire so that the strands are together as in a normal stranded wire. Fold the now-wireless insulation back on itself, leaving space at the bend for a little loop on top. <br /> <br /> Put a small zip tie through this not-yet-secured loop and zip it to form another small loop. This loop will be used as an attachment for a support line, and to secure the antenna wires. <br /> <br /> Take two insulated wires that are of identical length (length not critical, my wires were originally 44' long and now a bit shorter after the rebuild), strip about 5/8" from one end of each, and use an overhand knot to tie the stripped end of each wire to the zip tie. Be sure to leave a few inches beyond the knot. The goal is for the beyond-the-knot segments of the wire to not receive any tension, no matter how hard you pull on either of the wires. The wires from the twinlead will wrap around the stripped ends (but not yet). The wire size isn't critical either, I used 24-gauge stranded hookup wire as that is what I had on hand.<br /> <br /> Add a second zip tie to secure the loop in the twinlead. Be sure to run the antenna wires through the zip tie as shown. Cinch the zip tie down tight and trim off the end. <br /> <br /> On each side of the twinlead, twist the twinlead wires around the stripped ends of the antenna wires. Apply solder to the ends of these splices but don't allow solder to flow all the way up to the tops of the splices. The idea is to leave the top flexible, just in case tension ends up being applied to the splice (which should never happen, but best to be safe).<br /> <br /> You'd think (or at least I thought) that a single overhand knot would not be sufficient to keep the wire in place and not slip. However, the "corrugations" on the inside of the zip tie bite into the wires' insulation and hold them in place.I did some destructive pull tests and discovered that the 24-AWG wire will actually break at some other point in the wire before the knot gives way.
  • Put heat shrink tubing over the splice. I like to use two pieces on each splice for extra girth which is useful in the next step, but one piece per splice is probably sufficient.
  • Place the splices along side the twinlead and add two more small zip ties. These zip ties go around the both the twinlead and the splices. Cinch the zip ties down tight and trim off the ends. The zip ties will bite into both the twinlead insulation and the heat shrink tubing and thus be quite secure. FInally, trim off whatever extra twinlead insulation you have left beyond the zip ties and splices.
  • Add two more zip ties to secure the shrink-wrapped splices to the sides of the twinlead loop. Here you can see the zip ties and wire that I used.
  • On the other ends of the wires, I add a few 1.5-ish inch long pieces of heat shrink tubing to give that section of the wire more girth, bend it back on itself to form a loop, then use a third piece of heat shrink tubing (previously placed around the wire and the wire end threaded back through it) to hold the loop together. This is where I attach my end support lines. I also place a female blade connector on the ends so that I can add optional and rarely used extensions for getting on 160m (the extensions have a similar loop and mating connector, and I zip-tie the loops together).
  • These LaserPro line winders from IntoTheWInd.com (an online kite store) are great for keeping the antenna wires organized. Be sure to use a figure-8 wrap so that the wire will easily come off the winders with no twisting or kinks when you set up the antenna.
  • I place a dual banana plug on the other end of the twinlead for easy connection and disconnection to my baluns, which are equipped with female banana connectors using the same spacing.
  • Most people leave their end support lines connected to the antenna and wind the line and wire onto the same winder, but I prefer to use separate ones for more flexibility in setting up. The small blue winders are Innova Mini-Winders, also from IntoTheWind.com. The support lines are mason line from the hardware store. Velcro ties keep everything neat and tidy.
  • I put a fishing swivel and clip on the end of each mason line for attachment to the end loops on the antenna wires. The other end of the mason line is tied to the winder itself. This makes it easy to unspool as much line as you need, then cram the winder into a crack between rocks, set a rock on it, use branches on a tree limb to hold it, etc.<br /> <br /> So there you have it. I don't claim that this is the best construction technique for a doublet antenna, or even a good one, but hopefully it will hold up longer than my last one.
  • I use nylon and mesh deluxe ditty bags from Jandd Mountaineering to keep antennas and other items organized in my SOTA pack. On the right is a size C (10.5" x 14") bag with the doublet, 4:1 QRP balun, coax jumper for connecting the balun to the radio, and a spare coax jumper. On the left is a smaller size B (8" x 10") bag with my backup antenna: random wire, radial wire and BNC-to-banana/binding post adapter. The bags are available online from Jandd Mountaineering at jandd.com.
  • The front of the Jandd ditty bags is a zippered mesh enclosure and the back is made of nylon.
  • Can the Jandd dogs outpack WG0AT's goats?
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