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After you make the Slim Jim, I suggest you assess how good or bad you have made it. One way to do this is to measure antenna parameters. Unfortunately most DIY hobbyists don’t have costly and sophisticated test equipment required to measure antenna parameters and assess its performance.
The alternative left for hobbyist is to evaluate an antenna by COMPARISON with a reference. There are two easy references available for DIY hobbyists:
Comaparison #1: Determine what maximum possible range can be obtained at a particular location and antenna height, using method described in FIRST POST of thread What is the Maximum Range I can Get?. After this, also obtain maximum range curve of your antenna using VRS, and compare the two maximum range curves.
Comparison #2: Make an easy DIY 1/4 wavelength ground plane antenna (Quick Spider), swap the CoCo by Spider, keeping everything else same (i.e. same same location, height, coax to receiver etc.), and compare results.
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