A device which helps with receiver overload and spurious responses at VHF, UHF and above may be installed in the receiver front end. It is called a:

A helical resonator is a highly selective, high-Q bandpass filter consisting of a wire helix enclosed inside a conductive square or cylindrical shield. When installed in the front end of a VHF or UHF receiver, it acts as an excellent preselector, allowing only a very narrow band of desired frequencies to pass through to the sensitive mixer stages. By keeping overwhelmingly strong adjacent-band signals out of the sensitive receiver circuitry, the helical resonator prevents front-end overload, intermodulation distortion, and other spurious responses. While duplexers and diplexers also utilize resonant filtering, their primary purpose is to combine or separate different frequency paths (such as allowing a transmitter and receiver to safely share a single antenna). A directional coupler is an entirely different device used to sample RF power for measurement, offering no receiver filtering benefits.