Question T9B09
From subelement T9 - T9B
What can cause erratic changes in SWR?
Why is this correct?
Loose connections in the antenna or feed line cause erratic SWR changes because they create intermittent impedance mismatches. When connections are loose or corroded, the electrical contact varies unpredictably, causing the impedance seen by the transmitter to fluctuate. This results in unstable SWR readings that jump around. Thunderstorms, over-modulation, and strong local stations don't directly affect the physical impedance matching between your transmitter and antenna system.
Memory tip
Look for the physical cause when SWR behaves erratically. Electrical problems in the RF path (loose connections, corroded contacts, damaged coax) create variable impedance, while external factors like weather or other signals don't change your antenna system's fundamental electrical characteristics.
Learn more
Loose connections are like intermittent potholes in your transmission line's impedance highway. As the connection makes and breaks contact, it alternately presents different impedances to your transmitter. Modern solid-state transmitters detect these SWR fluctuations and may automatically reduce power or shut down to protect their output amplifiers. This is why maintaining clean, tight connections throughout your antenna system is critical for both efficient power transfer and equipment protection.
Think about it
Why would a loose connection create variable impedance readings while external RF interference would not affect your SWR measurements?