Today I’m going to show you how to make a 1/4 wavelength antenna for the 70cm amateur radio band. Of course physics doesn’t care who’s using her laws, so this design can be applied to really any frequency, though the lower in frequency you go, the bigger it gets! We’ll cover a little basic antenna theory, build it, install it in the attic and do some testing & tuning on a nanoVNA vector network analyzer.

**NOTE: If you are going to make one of these, the distance from the center of the SO239 to the edge of the metal plate MUST be considered as part of the radial system. So you MUST subtract this length from the wire radials when cutting them.

Sheet metal brake/shear used:
Harbor Freight discontinued it, but looks like it's been rebranded - albeit with an unfortunate name
https://www.amazon.com/KAKA-Mini-Shea...

Parts used in this build
3/4” OD PVC pipe
RCA antenna mount PN VH123R
1/8” Thick 6061 aluminum baseplate, 4” x 4”
4 Ground radials - Hobart 3/32” brass brazing rods
Larger 5/32” (0.014” wall) center brass radiating element - K&S Precision #1146
Smaller 1/8” (0.014” wall) (0.014” wall)telescoping center brass radiating element - K&S Precision #1145
Stainless 1” x 0.025” strap used for radial “holders” - K&S Precision #87167
12 4-40 screws
SO239 Connector

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