(QAM, Quadrature Amplitude Modulation) This digital frequency modulation technique is primarily used for sending data downstream over a coaxial cable network. 64QAM is efficient, supporting up to 28-Mbps peak transfer rates over a single 6-MHz channel. By comparison, 8-VSB will only support about 19.5-Mbps in terrestrial broadcast applications. QAM's susceptibility to interfering signals makes it ill suited to noisy transmissions.