The evolution of a 64 kbps HF data modem

With 9.6 kbps data rates over HF channels now gaining acceptance, the obvious next question is; how can we increase data rates beyond 9600 bps? Our view is that the bandwidth which our high data rate signal occupies must be increased. The most practical means for doing this is to use multiple 3 kHz channel allocations available within the current frequency management regime. We present the history which has led to the development of the high data rate multi-channel HF modem and discuss the merits of several approaches to multi-channel HF