The choice of data speed and modulation type was fortuitous, sounding much like the usual signal fading normally experienced with mobile repeater users. Avoiding user panic when trying new ideas goes a long way toward gaining acceptance. Of course, this system will not survive the hostilities of nearby transmitters. An experiment we are just beginning uses a combination of direct sequence and frequency hopping on 6 meters. Signal generation lends itself to NCO methods.
Coherent demodulation is required, significantly complicating the receiver.
Related Efforts Work is progressing in the context of IEEE 802.11 to define a standard for short range, interoperable spread spectrum data communications devices operating under Part 15 Rules . The major emphasis thus far has been placed on slow frequency hopping protocols using conventional FM-GFSK modulation. These papers are a very nice technical assessment of the interference-limited situation our radio service faces, and they also show the importance of having available the freedom to chose the technology appropriate to the problem. Successful SS realizations provide robust, interference-resistant links, and these results are satisfying indeed to achieve. Building and testing SS systems requires a variety of special talents.