Systems and methods for reducing interference by warbling a reader transmitted signal are described. To reduce interference in a densely packed multiple reader environment, a reader modulates or warbles the frequency or phase of the transmitted signal during a reception portion of a symbol exchange period. The transmitted signal is modulated within the bandwidth of an operating channel. The bandwidth of the operating channel is much narrower than the system bandwidth. In frequency warbling, the carrier frequency is shifted one or more times during the reception portion of the symbol exchange period. If phase warbling, the transmitted signal is spread within bandwidth of the operating channel during the reception portion of the symbol exchange period.