>From what I understand, we do not have an actual bandwidth limit on HF, but we >do have a practical one, based upon PART97 prohibitions against harmful >interference and of course the 300 baud limit.
The wider HF digital modes 'get around' the 300 baud limit by transmitting multiple streams, each at less than 300 baud inividually but adding up to something significantly higher. Q15x25 for example transmits fifteen PSK streams for an effective 2.5 kb data rate. The transmitted signal is about the same width as PACTOR III, around 2.5 kHz. The legality of 'getting around' the 300 baud limit with multiple streams has not been established. So far, the FCC has not put its foot down on the matter but that is no guarantee that they will not decide to do so at some point in the future, perhaps when and if they feel that the practice has gotten out of hand. The prohibition against deliberate harmful interference is the real limiting factor. We must remember that saying "I didn't listen before transmitting, so I didn't know I would interfere." is no defense whatsoever against a complaint of deliberate interference. It does not take a rocket scientist to know that if you transmit an ultra-wide signal on busy, crowded amateur radio spectrum without taking pains to find a clear spot of the required size, that you will most certainly end up crashing other hams QSOs. In light of this, and the fact that our spectrum is shared spectrum where nobody owns a frequency, you may wonder why we do not have a bandwidth limit on HF. There are a number of reasons for this, but the main one is that we are expected to experiment with radio technology, to push the envelope in various ways that may require more bandwidth than usual. This is something to consider if you are wondering why the FCC has not put their foot down so far on the 300 baud rule. They are giving us "leeway". Playing with ultra-wide signals on an occasional, experimental basis is not so difficult. As we all know, sometimes the HF bands are packed from one end to the other, and at other times there are great, wide stretches of unused spectrum out there. I'll mention here that the more useful and popular bits of spectrum ( 20m for example ) are going to be unoccupied a lot less often than 17 or 15m for example. So, for a careful and thoughtful experimenter, finding a stretch of open spectrum to play with a wide signal is not such a difficult thing to do. Not to mention VHF and UHF of course, the best and most reasonable place to experiment by far. Where we run into difficulties on HF is when we stop experimenting with wide modes and start attempting to use them on a regular basis. This is because we simply cannot realistically expect to find that much open HF spectrum on a useful frequency, in the same spot, on a regular basis. The problem is compounded when you attempt to utilize wide signals this way with an unattended, automated server. With no human there to look for times when the required amount of spectrum is open, we must depend upon 'signal detection' software and there are limitations to signal detection that make it progressively slower and uncertain as you sample a wider area for signals. I think we can all take it for granted that WinLink's "to hell with our fellow hams" approach of running wide signals with no signal detection whatsoever is not acceptible, and may well bring on the crackdown upon signals above 300 baud that I mentioned the possibility of, earlier. Thumbing their noses at the amateur radio community and the PART97 regulations that way cannot be realistically expected to return a good long-term outcome. They endanger us all as they test the FCC's patience this way. I have more to say about the inherent limits to signal detection but this post is getting too long already. So, we do not have a codified limit to bandwidth, but we do have a number of practical ones that should be easy to stay out of trouble with, as long as we play well with others and follow the rules. ( PART97 and The Amateurs Code ) Otherwise - we are asking for trouble and will not like the result that follows. 73 DE Charles Brabham, N5PVL Prefer to use radio for your amateur radio communications? - Stop by at HamRadioNet.Org ! http://www.hamradionet.org ----- Original Message ----- From: Dave Sparks To: digitalradio@yahoogroups.com Sent: Tuesday, October 27, 2009 9:17 PM Subject: Re: [digitalradio] Why would anyone I'm not sure who suggested 50-100 khz. of B/W... But if someone can take up 6 Khz of B/W just to transmit a human voice, why not something similar for digital modes? I'm not saying you SHOULD, or that it would be PRACTICAL, but if we're setting limits ... -- Dave Sparks AF6AS ----- Original Message ----- From: DANNY DOUGLAS To: digitalradio@yahoogroups.com Sent: Tuesday, October 27, 2009 7:02 PM Subject: Re: [digitalradio] Why would anyone OH Wonderful! Some idiot would come up with something 50 or 100 kc wide, and then be legal to wipe out dozens if not hundreds o QSOs. There MUST be rules, because there is always going to be someone who will push the envelope with so called "advances" which ignore the rights and wishes of others. Thats why we have speed limits even the Germans have finally come around to realizing you just cant let every Hans drive his own speed. By the way, 200 mph will get you there (if it doesnt kill you and everyone else on the road), but 60 will get you there too, and a lot safer. Danny Douglas N7DC ex WN5QMX ET2US WA5UKR ET3USA SV0WPP VS6DD N7DC/YV5 G5CTB All 2 years or more (except Novice) short stints at: DA/PA/SU/HZ/7X/DU CR9/7Y/KH7/5A/GW/GM/F Pls QSL direct, buro, or LOTW preferred, I Do not use, but as a courtesy do upload to eQSL for those who do. Moderator DXandTALK http://groups.yahoo.com/group/DXandTalk dxandt...@yahoogroups.com Moderator Digital_modes http://groups.yahoo.com/group/digital_modes/?yguid=341090159 ----- Original Message ----- From: Dave Sparks To: digitalradio@yahoogroups.com Sent: Tuesday, October 27, 2009 9:55 PM Subject: Re: [digitalradio] Why would anyone ----- Original Message ----- > From: Andy obrien > To: digitalradio@yahoogroups.com > Sent: Tuesday, October 27, 2009 3:57 PM > Subject: Re: [digitalradio] Why would anyone > > > > > I agree with Charles, mostly. I have mixed feelings about the whole > "wide" versus "narrow" issue. While I tend to gravitate towards the > narrow modes, I > have to admit to sympathizing with those on this list who express > frustration that they cannot experiment with some of the wider modes > because they exceed > baud rates and bandwidth limitations in the USA. Obviously, if I am > parked on my narrow part of the spectrum having a nice chat, I would be > unhappy about > someone with a 10 Khz wide signal zapping the entire band. I guess I > would say that keeping the max under 2.7 Khz makes some sense. > > Andy K3UK Hi Andy, That limitation would only make sense if you were also willing to ban DSB AM transmissions, which take up over twice that bandwidth. What we really need is a rule that says you should use the minimum bandwidth needed to get the job done, just as we do with power. -- Dave Sparks AF6AS
