Explanation: Shorted-stub lightning protectors rely on the principle of a quarter-wave transmission line stub. A quarter-wave (λ/4) section of transmission line, shorted at its end, exhibits a very high (ideally infinite) impedance at its input at the design frequency. This means the radio signal effectively "sees" an open circuit, allowing it to pass unimpeded to the antenna. However, a lightning strike, being a DC or very low-frequency transient, sees the direct short to ground and is shunted away from the equipment. This impedance transformation is highly frequency-dependent. If the operating frequency deviates significantly from the tuned frequency, the stub's electrical length is no longer λ/4, and it no longer presents an open circuit. Instead, it can become an impedance mismatch, attenuating the desired signal or providing ineffective protection. Therefore, these protectors are effective only at their specific tuned frequency band.