FlightAware Discussions

Length of radials on spider antenna

Was looking over different sites on how to build spiders and came across:
https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/

which, with adding in the velocity factor (which I keep forgetting) made me realize more why the vertical isn’t always best using the full 68.7mm length… But… why the additional 12% length for the legs?

I also saw the comments in My Spider gets complicated about having a horizontal component to the ground plane closer to the 1/4 wavelength (I’m currently soldering the legs to a 1" copper washer with a 5/16" hole to attach a F barrel connector). So would that also suggest that the horizontal component of the ground plane need to be 12% longer than the 1/4 wavelength as well, or should it be more in line with the length of the vertical element?

Without an impedance meter, you just need to be in the ballpark with your DIY 1/4 wave ground plane antenna. Browse this link for more background …

Length of legs is not critical.

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