LAB-

5.5 dBi Colinear antenna (868 MHz)
Found an easy way to construct a waterproof 868 MHz antenna for the rooftop, cutting bottlenecks to ease the winding of plain copper electricity wire. Based on the original design for welding wire from a youtube video

I just wanted to check if I could obtain a decent result using 2.5mm2 copperwire to get a colinear antenna. Straightened the plain copperwire using a drilling machine. Then made the windings around cut PETbottle necks (had to try several models to find the right ones corresponding to the bending radius). Used three of these caps on a piece of electrical pipe and taped everything at the right distance, taking care to add some 32mm pipe and a sleeve around every section before mounting the next bottleneck. Then connected a vector analyser and shortened the bottom section until the best results for 868 MHz (VSWR 1.06). The actual antenna = the 3 top sections including the Y under them. The bottom pipe is only there to reduce human influence during antenna measurement

To achieve great things, two things are needed: a plan, and not quite enough time.
(Leonard Bernstein)

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