Building the W8NX Short Trap Dipole

For the past five years, I have been operating the lower bands (30, 40 and 80 meters) with a trap dipole that was modeled after a web article written by John DeGood NU3E. [1] While the antenna performed well, a monsoon storm last summer beat it up enough that the antenna wire broke at the center balun.

So I climbed the tower and lowered the remains of the antenna to the ground for repairs. On closer examination, I discovered that the relentless Arizona sun had taken its toll on the traps. The insulation on the exposed ends of the coax had rotted away. They were still working, but would need to be rebuilt and weatherized to insure good operation many years into the future.

Since I was going to have to rebuild the antenna, I started thinking about whether this antenna met my current needs and wishes. I had been wanting to get on 160 meters at this QTH for some time, but my small back yard would not accommodate an antenna of that size with conventional coaxial traps.

Some research led me to a QST article for a short 40, 80 and 160 meter trap dipole. [2][3] This design used double-wound traps made from only the inner conductor of RG-58 coax. The trap design was a little more complicated, but would almost fit into my back yard. I decided to pursue construction of this antenna, and bend the 160 meter end wire, if necessary to fit into the yard. A tradeoff of the loss of 30 meters for the addition of 160 meters fit my operating needs well.

In the construction of my prior trap dipole, I had used my MFJ-259B antenna analyzer to measure and adjust the traps and wire lengths. Since that time, I have acquired one of the new, cheap NanoVNA vector network analyzers[4][5]. It looked like the nanovna might make the job a little easier and present a clearer picture of the antenna characteristics. So I set off to construct my version of the W8NX short trapped dipole. Follow along for details and tips on how you might build this unique classic trap dipole for the lower bands.

W8NX Trap Dipole cut for Center Band
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Rebuilding the 80-40-30 Meter Trap Dipole

After more than 5 years of operation, one of the antenna leads on my homebrew 80-40-30 Meter Dipole broke at the center balun connection.

This dipole has served me well, allowing me to easily utilize those lower HF bands. While I did not use 30 meters much, it was nice being able to go there when I wanted to.

I climbed the tower and lowered the entire antenna to the ground. Once I was back in the shack, a quick look made it obvious that I needed to better weatherize the traps. The sun had pretty much destroyed the exposed inner conductor of the coax on the inside of the trap forms. With this in mind, I went about rebuilding the traps with new coax.

Trap Test Setup with NanoVNA
Trap Test Setup with NanaVNA
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B&W Antenna Switch Repair

Some time in the past, I have picked up several of the B&W Antenna Switches at a hamfest. They were purchased at a good price, just $10 each, and appear to be of pretty good quality. I got two 6-position switches (B&W Model 595), and two 3-position switches (B&W Model 593).

Last month, I decided to put them to use in my remodeled hamshack. So I dug them out of the parts bins, and gave them a quick multimeter test.

One of the 6-position switches had a problem with the grounding arrangements for unused connections. As they are switched from antenna to antenna, they are supposed to put a ground on all connections except the one currently in use. This switch was not doing that.

B&W 595 Antenna Switch as Received
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Kenwood SW-2000 Wattmeter Lamp Replacement

I’ve been busy lately rewiring my hamshack. In the process, I have been doing some minor repairs to equipment that has deteriorated over the years.

My Station Wattmeter, a Kenwood SW-2000 that I bought new in 1983, had long ago burned out its incandescent bulbs for the meters. So it is time to replace them with some new LED bulbs.

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3018 CNC for PCB Milling?

I have started learning how to mill PCB boards using a benchtop CNC Router.

3018 CNC Assemble
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