This is a simple center block for the construction of a quarter wave ground plane antenna. You just need some solid wire and glue. The four bottom wires go in a 45 degree angle, all connected to ground.

Calculate the length you need: https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/

The antenna in the pictures is an AIS antenna, make your own AIS station with a Raspberry Pi and a DIY antenna: https://github.com/innovationgarage/ElCheapoAIS