ttrftech(edy555) published open source/hardware Vector Network Analyzer (VNA) called NanoVNA and hugen79 designed LiPo battery circuit. VNA is used to measure antenna performance.
In this picture , a hand made loop antenna for HF band shows 16MHz resonance frequency.
NanoVNA improved hand made AWX antenna for ADS-B receiver.
NanoVNA-H v3.4 is available from amazon.co.jp at about $60.