Causes that may affect the quality of shortwave data communication over radio are presented. Designing an audio-frequency filter unit, other than the filters exist in the transceiver, is considered as one solution to improve the quality of this shortwave data communication. Among the different data communication modes exist in the communication system, the CW (continuous wave), RTTY (Radio teletype) and AMTOR (amateur teleprinting over radio) types are selected to test the performance of the designed filter unit. The filter unit is of FIR digital filter type which the impulse response coefficients are obtained using the Kaiser Window design technique. The DSK (digital signal processor starter kit) assembler and debugger are used to develop the assembly code so as to realize and implement the filter on TMS320C50 digital signal processor. The magnitude response of the resulting filter unit is estimated by a spectrum analyzer. Finally, the designed filter unit is tested in an Amateur Radio Communication System.