A technique for reducing interference between a direct-sequence ultra-wideband communications system and a narrowband communications system uses interference-rejecting spreading codes to reduce signal power in a frequency band associated with the narrowband communications system. A method of operating an ultra-wideband communications system includes applying an interference-rejecting spreading code to a signal for transmission. The interference-rejecting spreading code is configured to reduce power in a particular frequency band of a transmit or receive power spectral density associated with the ultra-wideband signal without substantially reducing power outside that particular frequency band of the transmit or receive power spectral density associated with the ultra-wideband signal.