2. Small desired signals in RF circuit simulation are crucial for accurate system processing and need to be carefully amplified and filtered without being degraded by noise or interference. 3. Large interference signals in RF circuit simulation can significantly degrade system performance and must be minimized through shielding, grounding, and proper layout and routing of traces. 4. Adjacent channel interference in RF circuit simulation can cause signal distortion and degradation, requiring careful consideration of frequency channel spacing, isolation, and filtering in PCB board design.