According to Part 97 of the FCC rules (specifically §97.221 Automatically controlled digital station) automatically controlled digital stations have 134.5kHz of space to work in on the the HF bands (10 meters through 80 meters). Breaking this bandwidth up into 500 Hz channels* we see that we have 269 spaces for digital stations to work. The breakdown is as follows:
Frequency | Bandwidth | Channels ------------------------|-----------|------------- 28.120 MHz - 28.189 MHz | 69 kHz | 138 channels (57 channels @ 1200 baud) 24.925 MHz - 24.930 MHz | 5 kHz | 10 channels 21.090 MHz - 21.100 MHz | 10 kHz | 20 channels 18.105 MHz - 18.110 MHz | 5 kHz | 10 channels 14.095 MHz - 14.0995 MHz| 4.5 kHz | 9 channels 14.1005 MHz - 14.112 MHz| 11 kHz | 21 channels 10.140 MHz - 10.150 MHz | 10 kHz | 20 channels 7.100 MHz - 7.105 MHz | 5 kHz | 10 channels 3.585 MHz - 3.600 MHz | 15 kHz | 30 channels
So we can easily see where we have the most areas to play. Ten meters may be a bit misleading as you can run 1200 baud packet there. So who is operating on all these frequencies? Looking backwards (longest wavelength first) we see the following channel users:
3.5850 MHz - WL2K 3.5859 MHz - NTSD ... 3.5870 MHz - WL2K, NTSD 3.5872 MHz - WL2K ... 3.5890 MHz - WL2K ... 3.5900 MHz - WL2K ... 3.5909 MHz - NTSD 3.5910 MHz - WL2K 3.5919 MHz - NTSD ... 3.5930 MHz - WL2K 3.5935 MHz - NTSD ... 3.5950 MHz - WL2K ... 3.5970 MHz - NTSD 3.5979 MHz - NTSD ... 7.1004 MHz - NTSD ... 7.1011 MHz - NTSD 7.1012 MHz - WL2K 7.1014 MHz - NTSD 7.1015 MHz - WL2K 7.1017 MHz - WL2K 7.1019 MHz - WL2K 7.1024 MHz - WL2K, NTSD 7.1029 MHz - NTSD 7.1030 MHz - WL2K 7.1034 MHz - WL2K, NTSD 7.1035 MHz - WL2K, US Packet 7.1037 MHz - WL2K 7.1039 MHz - NTSD ... 7.1044 MHz - WL2K 10.1409 MHz - NTSD 10.1412 MHz - WL2K 10.1419 MHz - NTSD 10.1420 MHz - WL2K 10.1429 MHz - NTSD 10.1434 MHz - WL2K 10.1437 MHz - WL2K ... 10.1449 MHz - NTSD 10.1450 MHz - WL2K 10.1455 MHz - WL2K 10.1459 MHz - NTSD 10.1462 MHz - WL2K 10.1465 MHz - WL2K 10.1467 MHz - US Packet 10.1470 MHz - WL2K 10.1477 MHz - WL2K ... 14.0959 MHz - NTSD 14.0962 MHz - WL2K ... 14.0974 MHz - NTSD 14.0978 MHz - US Packet 14.0979 MHz - NTSD 14.0980 MHz - WL2K 14.0985 MHz - WL2K 14.0987 MHz - WL2K ... 14.1027 MHz - WL2K ... 14.1042 MHz - WL2K ... 14.1067 MHz - WL2K ... 14.1080 MHz - WL2K 14.1085 MHz - WL2K 14.1089 MHz - WL2K ... 14.1099 MHz - WL2K 14.1100 MHz - WL2K ... 14.1120 MHz - WL2K ... 18.1062 MHz - WL2K 18.1069 MHz - WL2K ... 21.0934 MHz - NTSD 21.0987 MHz - WL2K (All frequencies are center. WL2K and NTSD station frequency list pulled on 19 October 2011. Incomplete listing of US Packet SKIPNETs. Only US stations included in the listing.)
So are we using our frequencies in a channelized fashion? No we are not. What does that mean? That means that the overall efficiency of our spectrum is reduced. If you have a station between two channels transmitting they are basically occupying two channels instead of one. Is this a problem? Maybe. I've heard several times two stations transmitting where they were clearly overlapping causing neither station to communicate with who they were attempting to talk with. But from where I'm listening (40 meters) it's rare. The use of PACTOR-III makes things worse, however, as these stations transmit 2kHz-wide signals taking up four channels. These stations also get on and off the frequencies faster as well so they aren't taking up any channels as long as a regular 500 Hz station would. (Yes, we are TDMA.) You can tell by the ellipses I've included in the chart where there are gaps in known usage. That means that there is still room for new stations to come up on HF and utilize the spectrum.
Would it be better to have a "frequency coordinator" of sorts working with all HF networks to spread stations out and make better use of the spectrum we have? Probably wouldn't hurt. Is it necessary? Probably not; at least not now.
And remember that band that has 69kHz of available spectrum? No one claims to be there...
* There is nothing that says we have to channelize our spectrum here but to not do so would be incredibly wasteful and could lead to interference.