KH6TY wrote: > It will be spread spectrum if the tone frequencies are controlled by a > code as explained in the ROS documentation: > > "A system is defined to be a spread-spectrum system if it fulfills the > following requirements: > 1. The signal occupies a bandwidth much in excess of the minimum > bandwidth necessary to send the information. > 2. Spreading is accomplished by means of a spreading signal, often > called a code signal, which is independent of the data. > 3. At the receiver, despreading (recovering the original data) is > accomplished by the correlation of the received spread signal with a > synchronized replica of the spreading signal used to spread the > information. > Standard modulation schemes as frequency modulation and pulse code > modulation also spread the spectrum of an information signal, but they > do not qualify as spread-spectrum systems since they do not satisfy > all the conditions outlined above. > > Note that all three conditions must be met to be considered spread > spectrum. I don;t know if it would be possible to send the data in > less bandwidth, but, for example, PSK31 accomplishes the same typing > speed in a bandwidth of 31 Hz, instead of in 2000 Hz, so ROS is > probably truly spread-spectrum. >
The key is the "much in excess" in item 1. If you were to use 31hz vs 2000, you'd be approaching the minimum bandwidth expansion factor in practical usage at 64:1. I'd have to go look at realistic bandwidth for psk, I was thinking it's a bit higher in the real world. Modern SS runs way higher, often 1000:1. But just like the fsk symbol rate anachronism in the regs, I suspect the spread spectrum restriction in the regs was targeted the very broad (50-100khz minimum) spread spectrum signals. Realistically, they did not anticipate that we'd have the capability to do SS in a 2khz signal. (and we probably could not have pre-sound card) But after reading the NTIA definition, and the one in the docs, I agree it's technically SS by a strict interpretation. Just like P3 is technically FDM. But since both live in a SSB signal bandwidth, they are not what the regs were trying to prevent. Based on the FCC ruling on P3 OFDM, my suspicion is they'd fall in favor of ROS. I don't see a practical reason for them to disallow it, it does not have expanded footprint, etc. But all this points out to me how out of date the US regs are! It would be easier if they had used the NTIA definition, and ideally put some practical measures around bandwidth expansion factor and overall bandwidth. No matter what, it's a neat idea, and thanks for taking the time to code it! have fun, Alan km4ba
