Dave wrote: > > > The closest you get to a true definition in Part 97 is in section 97.3 > Definitions, Para C, line 8: > > /(8) SS/. Spread-spectrum emissions using bandwidth-expansion > modulation emissions having designators with A, C, D, F, G, H, J > or R as the first symbol; X as the second symbol; X as the third > symbol. >
I disagree, that's not a definition of Spread Spectrum, it's a restriction on spread spectrum. And not a very useful one, as in it's not specific enough to entirely limit the (presumably) bad SS, and yet it may disallow modes which are not the target. All due to poor wording. You have to define bandwidth expansion. I'm rusty, but it's normally when the impacted bandwidth (think footprint) used exceeds the information bandwidth. Which itself is usually something less than the Shannon limit. What they are really saying is bandwidth expansion *factor* greater than one, and for nearly all traditional spread spectrum (Frequency Hopping & direct sequence) that is a factor of 20 to 250 or more. We could argue whether mode X is legal or not, but if you are going to be legalistic, then modulated CW is illegal as well as it's bandwidth is greater than the information bandwidth. (bandwidth expansion > 1) And even regular CW, PSK, and others when the gear is not operated correctly. Bandwidth > information bandwidth is a harsh measure! Even some SSB voice stations could be at risk! :-) Realistically, many modems use "spread spectrum" type approaches to spread & randomize the energy inside the typical voice/SSB bandwidth. The FCC cares about bandwidth. We know from the "symbol rate" rulings that they are not inclined to deal with overly strict legal interpretation on wording. The symbol rate restriction is used as a (bad) analog for bandwidth, as it's what was used when the regs were made. So the same type arguments surfaced around symbol rate (real vs theoretical, etc). And we know from all the Pactor 3 on the air how that ended up! So at the risk of being an armchair lawyer as well, I do think you have to apply some "rule of reason". What's the intent of the restriction? To not allow direct or random sequence spread spectrum on the lower bands. Largely defined by DS-CDMA & FS-CDMA approaches used as the "classical" spread spectrum modes. This is what the military uses, what the VHF/UHF devices use, etc. And they have much larger footprints (bandwidth expansion of 20 or more), so should not be allowed on HF. Really what we are talking about is an afsk'ish soundcard mode that stays in one SSB bandwidth slot or less. Is it classical spread spectrum? Clearly not. Is it technically spread spectrum? Would depend on exact semantic definitions. But since the implied dial/carrier frequency does not move, is detectable without extreme measures, and is not going to effectively raise the noise floor of the entire HF band, I would be very surprised to see the FCC wade in and say it's spread spectrum. > ROS uses SSB so the first designator is J (this meets the definition) > and it uses bandwidth-expansion. (this meets that definition as well) > Thus, taking this definition literally, it is indeed Spread Spectrum > and is thus illegal below 222MHz....at least that the conservative > interpretation that I'll stick with until we get a ruling otherwise. So using your literal test, modulated CW is not legal, as it's J and has bandwidth expansion factor > 1 in the real world. You could question several AFSK modes as typically used by hams. (artifacts and all). Each time we go to the FCC for things like this it's like small children going to the teacher and asking "is this allowed?". There is a certain amount of impatience, and based on past discussions/interpretations the FCC will lean toward common sense interpretations. Largely defined by bandwidth, crypto definitions and not obscure technical definitions. Ideally, we'd have a reasonable approach to using our spectrum. I think there is 2-3 options in use in other countries we could adopt that would simplify this type issue and result in "no net loss" for current legacy modes. Yet they always dies with FUD from the broader community without being debated on their merits. There is no option to rationally discuss, it's all or nothing. So we get to pay the price with digital definitions based on 30's (or older) technology. Just about all the modes which achieve good weak signal performance do so by trading off effective throughput for bandwidth. Some are more efficient than others in this regard. Do I think the FCC cares about another soundcard mode that lives politely in a single SSB width signal? Nope, as long as it's not encrypted. But that's just my read. I'm sure we'll have many others! :-) Have fun, Alan km4ba
