Why Noise is the "Enemy" HF signals naturally propagate over long distances by reflecting off the ionosphere (skywave transmission), but this also makes them highly susceptible to interference from both natural and man-made sources. A high noise floor can make it impossible to hear weak, distant signals, effectively "deafening" the receiver and limiting the operator's ability to communicate. Primary Sources of HF Noise Noise on the HF bands typically originates from two main categories: Man-made