W2XJ wrote: > > > It is generally accepted that 10 times bandwidth is the minimum > necessary to achieve enough processing gain to make the use of SS > worthwhile.
Not only is it not worth doing, it also increased chances of interference. I'm not aware of any weak signal DSSS using spreading factors of less than 100. The lowest I've seen is 16 for consumer strong signal wide band stuff. And that's just due to economics, not for performance. Take that same psk'ish data rate, use a more conventional spreading factor of 128, and you could see decent weak signal performance due to processor gain, and most likely not impact strong signal legacy modes in the same band segment. Of course, you could not do this with an audio SSB approach. But you could certainly decode it with SDR, which is why we should not throw out the baby with the bathwater. Remember, ROS somewhat sucked because it's spreading was so small there was a large likelihood of any given bit interfering with another weak signal. Spread that out, and it's only the individual "chips" (fraction of a data bit) that is on any given frequency at any given time. Put another way, you could probably run multiple DSSS signals at psk data rates in the SSB (voice) sub-bands with minimal impact to existing qso's if spread like conventional DSSS. You could see the impact on a properly setup monitor, but realistically the SSB stations would not detect the chips in their slot. Not that I'm proposing we do so, just that we need to fully understand the technology, it's potential advantages & impacts before we throw it out. All that said, I'm not expecting to see any SS on HF by hams in the next decade or two. I view it as a lost cause and we'll just learn to deal with the beeps & bloops from advance digital modes from non-amateur services on our shared bands. Have fun, Alan km4ba