A serial tone ECCM modem for HF channels

An HF ECCM modem based on a slow-hopped serial tone waveform has been developed at the RF Communications Division of the Harris Corporation. The waveform is based on a PN-spread PSK signal format and employs convolutional forward error correction and interleaving. The receive signal processing utilizes data-directed channel equalization, soft-decision-based Viterbi decoding, and narrowband interference excision to provide an HF ECCM capability with performance near that of fixed frequency serial tone modems. This paper presents initial design goals, an implementation overview of both the synchronization and data-passing aspects of the ECCM modem, and final modem performance.