On-air results of spatial diversity for the MIL-STD-188-110B Appendix C (STANAG 4539) 9600 bps waveform

In the early days of HF communications, CW and FSK waveforms were the prevalent means for data communications. These tone based signaling methods were very susceptible to frequency selective fading caused by multipath. To improve the reliability of these links, spatial diversity was commonly used. As newer, more robust waveforms were developed for HF, it was felt that spatial diversity was no longer needed. This paper investigates possible on-air performance improvements of using spatial diversity on modern HF waveforms such as the high data rate waveforms defined in US MIL-STD-188-110B.