L

0.25"

Side View

Fig 5—Driven-element mounting-plate details.

I soldered the shield to the brass and the center conductors to the center pin. Like the driven-element connection's insulator, I made the brass L long enough to securely tape the coax and provide strain relief.

Solid-dielectric coax seems to be reasonably consistent in terms of velocity factor, so the trimming often necessary with other types may not be necessary. Still, there's a good way of accounting for discontinuities such as coax connectors: Substitute a 24 Q resistor for the driven element and use an antenna analyzer to figure out what frequency the matching network is cut for—and then re-cut it to the proper length. Make sure the resistor is reasonable noninductive; that's something the antenna analyzer can also test. If you do this with a 10 foot length of coax, you can build three matching sections and not need to unsolder any connectors. You first measure what frequency the 10 foot section works at, and then the shorter 3 foot sections. Since a 3/a X matching section performs similarly to a % section, you might use this fact if your measurement technique doesn't cover much lower frequencies.

Fig 5 shows the pieces of Lexan I use to attach the UG-58 panel jack to the mounting plate. The half-inch hole in the T-shaped piece is a little tricky—I drilled it just deep enough to hold the hex bolt head. This captures the screw and prevents it from turning when you screw on a wing nut. The smaller pieces go on top of the larger pieces and the T-shaped piece keeps the element halves separated. The little top piece is for mounting the N connector. I use pieces of copper strap to attach the connector to the element halves. These straps are 0.3x2.0 inches long, with mounting holes drilled 0.2 inches from each end. Attach them to the driven element and N connector with #4-40 hardware. For the connections to aluminum tubing, I drill a #43 hole V*inch from the ends. Then I enlarge the closer hole with a #33 drill and the far end with a #4-40 tap. The straps are then attached with 9/ie inch long #4-40 screws and #4 lockwashers. It helps to coat the ends of the straps with solder to reduce corrosion. Finally, I coated the electrical connections with nonacidic Dow 3140 RTV.

The exact specification of Yagi dimensions can be a bit confusing. Often, one gets a taper schedule like that in Table 1.

For the cognoscenti, this is enough to build the antenna. Beginners need a

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