John wrote: > Thanks Skip, > > Unfortunately, this really does not get to the crux of my question(s). I > understand how an SSB transmitter works, but that is not really what I am > after. > > What I am driving at is if like this. If I use DM780 to run some version of > digital mode via an SSB transceiver, it uses a tone or series of tone > modulation/shifting to create the output of the transmitter, and not one > single mode is called "spread spectrum" output, but is called FSK or PSK, > etc. Now, we get into the aforementioned discussion regarding ROS, and > suddenly, still via the microphone input of the same transmitter, those > shifted frequencies are now called "spread spectrum" instead. I am having a > great deal of difficulty understanding, other than the author happened to > call his scheme "spread spectrum" in his technical documentation. >
OFDM used in Pactor 3 is legal due to it's low symbol rates and SSB sized effective bandwidth. If prior to P3 someone asked if FDM was legal on HF most would say no. Traditional FDM (frequency division multiplexing) as practiced in the real world would not ever be legal on HF. So technically it's FDM, but practically, it's not, as it's much narrower bandwidth. Lumping ROS in with Spread spectrum is similar. You can use FDM or SS approaches on an audio modulated sideband signal and not meet practical definitions. quack test- walks like a duck, must be a duck. Regarding the perfect SSB transmitter sending a 1khz tone equaling CW at a 1khz beat frequency, we all know there is a big difference between theoretical and reality. But in theory, ROS, P3, whatever could be represented by multiple transmitter signals, so could technically fall into legal gray area. I'm sure if we tried hard enough we could find a way to decide it's illegal, and should be banned. And in reality, the FCC won't care, as it did not meet the quack test of spread spectrum. :-) I don't have a horse in this race, however. :-) Have fun, Alan KM4BA
