There are a number of important impairments on a HF channel that affect received signal quality. Different signals are affected in different ways and in severity. Digital data transmission can be severely affected by dispersion, both in the time domain and in the frequency domain. Analog transmission is much less affected, as is CW. FSK is much more tolerant than coherent PSK. Signal-to-noise ratio requirements are a function of signal type. Table 12.3 reviews some typical HF waveforms (signal modulation types), required bandwidths, and signal-to-noise ratios.

Much of the thrust in this section is on digital transmission. At the end of the section we will briefly discuss medium-related impairments to analog transmission.

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