It’s high time I posted a few pics of my new antenna. First, the loading coil. This was made from a stock MFJ inductor (3″ dia, 10 turns/inch). the center rod is a nylon rod I purchased from U.S. Plastic, and the brass fittings are 1/8″ NPT couplers and a nipple from McMaster-Carr.

pict0006Here’s an end view of the loading coil. See how alternating turns are pushed in to make it easier to tap. You can also see the 1/8″ brass rod used to support the coil. I used a small butane torch to solder all the brass stuff.

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Here’s a view of the entire antenna. It’s situated at the corner of a gazebo-like structure. The support bracket toward the top was fashioned from some aluminum flashing I had on hand. I know the antenna’s a little crooked. It’s hard to get the brass couplers onto the nylon rod (in the center of the loading coil) straight…

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Here’s the base of the antenna, showing some of the ground radials, too. Pardon the black plastic tape–a little temporary repair job that I still gotta fix…

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As I’ve said before, much of the construction technique is taken from AD5X’s ultimate portable vertical design. I added the aluminum plate at the base for attaching the radials, and I decided to use the single six-foot aluminum tube with brass capacity hat at the top, rather than the telescoping whip that he used in his design. I did this mostly to make it more sturdy, but also to reduce its visual footprint a little bit.

Yesterday afternoon the thought popped into my head that my new “20m” shortened vertical might be just about the right height to be a full-size vertical for 17m. So, when I got home from work I completely bypassed the loading coil on the antenna, fired up the rig, and found an SWR of 1.5:1 on 18.1 MHz. Not bad! Then I thought, “What the heck–see what the SWR is on 15m!” So I tuned to 21.1 MHz, keyed up, and saw that the SWR was just a shade under 2:1. Not optimum by any means, but certainly usable. Finally, I spent a little time and found the right coil tap for 30m. No surprise that I can make it work on 30m–the SWR was about 1.2:1.

So, it turns out that this is a five-band antenna. So I’m just gonna call it my homebrew short vertical from now on. I need to run the 4Nec2 model again, too, just to see if it predicts the same SWR on 15 and 17m. Remind me, too, to post the model files here…

I’ve only made two contacts so far–PSK31 contacts on 20m and 40m, but hopefully I’ll get a chance to give it more of a workout this weekend.

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