A block coding algorithm called the spectral-shaping code (SSC) is introduced for the purposes of interference suppression in HF communication systems. The SSC code will effectively suppress DC and other unwanted frequency components in the baseband single whilst being much less complex than say adaptive antenna techniques. First, the condition for obtaining a DC spectral null is given, then the condition for obtaining a null at other values of frequency is derived. Finally, the method of obtaining the corresponding codeword by solving a set of linear equations is presented.