What can cause erratic changes in SWR?

The Standing Wave Ratio (SWR) measures the impedance match between your transmitter, feed line, and antenna. A loose connection causes the electrical continuity and impedance of the system to rapidly fluctuate as the wire or connector shifts physically. As the connection makes and breaks, or changes resistance in the wind, the SWR meter will show erratic, jumping readings. Weather events like thunderstorms, radio over-modulation, or nearby strong stations generally do not cause mechanical impedance fluctuations in your physical feed line system.