What do the upper/lower antenna band suppression filters (notch filters) do?

• A. They amplify Link 16 signals
• B. They protect the IFF transponder/interrogator from MIDS emissions and IPF monitor from IF emissions
• C. They provide airspeed data to the MIDS network
• D. They supply power to the MIDS terminal

Answer: (B)

Notch filters are narrowband filters placed in the antenna path to suppress specific frequencies that could cause interference with nearby systems. In a MIDS/Link 16 setup, the upper and lower band suppression filters are tuned to attenuate energy at particular frequencies so that strong MIDS emissions don’t bleed into the IFF transponder/interrogator, protecting it from interference. They also reduce energy in the intermediate-frequency path to keep the IPF monitor from being affected by IF emissions. These filters don’t amplify signals, transfer data, or provide power—they simply block problematic frequencies to keep adjacent systems operating cleanly.