What instrument is useful in adjusting the physical length of an antenna?

An antenna analyzer is a specialized test instrument that generates a low-power RF signal to measure an antenna's resonant frequency, impedance, and Standing Wave Ratio (SWR). By observing these readings, you can easily determine whether the physical length of an antenna needs to be shortened or lengthened to resonate at your desired frequency. Other common tools like multimeters are designed for DC or low-frequency AC circuits to measure basic voltage, current, and continuity. They cannot measure RF resonance or SWR, making them useless for adjusting an antenna's physical length.