What can cause erratic changes in SWR?

A loose connection in the antenna or feed line can cause erratic changes in Standing Wave Ratio (SWR) because it directly affects the impedance match between the transmission line and the antenna. When the connection is not secure, it can create fluctuations in the reflected power, leading to variations in SWR measurement. SWR is a critical parameter in antenna systems as it indicates the efficiency of power being radiated and the load's impedance characteristics. If the connection is intermittently shutting on and off or creating differing levels of resistance, the resulting SWR readings will reflect that instability.

Factors such as local thunderstorms may influence atmospheric conditions but do not typically create immediate issues with SWR readings like physical connections do. Similarly, over-modulation and overload from strong local stations can impact signal quality and reception, but these are more related to the distortion of the signal rather than the direct impedance mismatch reflected by changes in SWR.