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new dipole

Following my antenna analyzer project, I figured I’d put up a better antenna now that I have some rough way to measure resonance. At first, I was looking to make a 40m/20m multiband dipole. Using some spare rg-6 coax and some 14 gauge stranded AC line, I measured out my wire and constructed the dipole.

40_20_dipole_web1This is what I ended up with. A waterproof box with the 40m line on top, the 20m line below it, and the rg-6 entering from the bottom. Inside the box was a toroidal balun and those green things are old hard drive brackets I was planning to use as spacers. I put out the antenna and tested it with my antenna analyzer and swr meters and was getting some weird readings. I left the lines a little long so I started trimming them down. I kept trimming and trimming, but was still getting weird readings until I knew that I trimmed too much. This was my first multiband dipole so I may have done something wrong. I never did get any decent measurements, so I ended up scrapping the whole thing and I started over from scratch.

This time, I went with just the 40 meter band with the option to add other bands later. I also picked up a larger box and instead of a toroidal balun, I used an ugly balun on a piece of 3″ pvc. I also took more pictures this time around.

First, I took the PVC and cut it down to about a foot long section and drilled in some holes to feed in the coax.

ugly_balun_pvc_web

I used the same rg-6 from before and wound it through the pvc. The coil should consist of about 18 to 21 feet of coax. I ended up with 21 turns.

ugly_balun_coil_web

I taped up the coil to hold it in place. I eventually taped around the whole coil.

ugly_balun_taped_web

Next I drilled out the waterproof box and ran the stripped rg-6 and 14 gauge AC line into the box. I tied knots in the AC line for strain relief and then soldered the center conductor of the coax to one end of the AC line and used a wire nut to connect the coax braid to the other end. I twisted off several other sections of the braid so I can add more bands later if I wanted.

inside_dipole_web

Next, I sealed up around the cables with silicone and started testing. I hung the antenna and tested with the antenna analyzer.

dipole_graph

I don’t think my analyser is particularly accurate, but it shows that the antenna is resonant at 6.9 – 7.0 MHz, which is close enough. I also checked it with two SWR meters and was at 1.1:1 on one and 1.2:1 on the other.

Now that the measurements are looking good, I can permanently fix the ends. For the end insulators, I used electric fence insulators that I picked up from the local farm supply store.

fence_insultator_web

I added some heat shrink on one end, but it was more of a hindrance than a help, but I wrapped and soldered the end back on itself and wrapped it around the insulator. I taped up the ends with duct tape to somewhat waterproof it.

dipole_end_web

dipole_end_final_web

Next, I added a PL-259 connector to the end of the rg-6. The best way that I have found to do that is to strip the coax and then wrap about 5 to 6 turns of duct tape on the insulation where the cable was stripped. Don’t forget to add your heat shrink before the connector.

rg6_stripped_web

Next, fold back the braid and strip the dielectric to about 1/4 inch above the braid.

rg6_braid_web

Then add your connector. The duct tape should fatten up the cable enough for the screw on connector to bite into it. Next, I shrank down the heat shrink on the end and soldered in the center conductor.

pl259_web

I hung the antenna about 15 feet up a tree on top of a hill next to my house which makes it about 30 feet or so above my driveway. That is about the best location I have and it seems to be working well. The furthest station that I have heard so far is about 2000 miles away. I haven’t tried making any contacts yet. I still only have a ~5 watt qrp cw transmitter and I’m still getting up my morse code speed. I may put out a CQ and see if I show up on the reverse beacon network just to see how well it is working.

dipole_up_web

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