The maximum accepted bandwidth for most modes is the width of an SSB transmitter since you can not go wider than that and communicate with the typical rigs of the day.
We already have the basic modes to work high speeds with good conditions and slower speeds under difficult conditions. What we don't have are the types of ARQ modes that are adaptive to those conditions. It seems that the serial tone modems might work close to the MUF, but parallel tone modems are typically superior for a wider array of conditions. So my thinking is that we would want an adaptive parallel tone modem that can change the number of tones, spacing of the tones, length of tones, and modulation of the tones, to dynamically meet the conditions. When conditions get down below zero db S/N, the mode may have to change to the ones that can handle working deeper into the noise. And another factor would be to have the ability for the operator to select the maximum bandwidth they wish to use. Maybe that might be only 500 Hz, but maybe a lot more for certain purposes such as sending larger amounts of data, images/documents, emergency communications, etc. If it wasn't for the potential for supporting emergency communications, none of this would really matter very much since we rarely would need to send large amounts of data for typical radio amateur chats and the superficial hello/goodbye type contacts that most radio amateurs prefer. 73, Rick, KV9U Mark Miller wrote: >Walt, > >I think there is no doubt that this is true. The question I have >been struggling with is how much is enough/too much. I guess what I >am looking for is a curve showing bandwidth vs. throughput for >parallel tone modems, or maybe more precisely where is the point of >diminishing returns? I am sure there are many factors that would >affect the curves. I know from experience that MT63 is a great mode >when making very long and many hop contacts. I have watched the >fading move across the waterfall, and my text be 100% correct. I am >sure that this is because of the redundancy of the code spread out >over many frequencies. MFSK16 sometimes performs better under >certain conditions with a quarter of the bandwidth. What my question >boils down to is generally, what is the accepted maximum bandwidth of >any signal in the Amateur HF bands, given the finite spectrum and >many interests? > > >