Looking-Glass,
I always appreciate the extensive replies you put together and the monitoring time you put in trying to find out these mystery stations. So 8076 kHz USB is some sort of missionary radio network (not a broadcaster) using HF to communicate with their remote missions. Have you heard any actual callsign callsigns? That is, a FCC-issued callsign (generally alphanumeric, beginning with K or W - land mobile stations are K or W, only US Navy and aircraft use the N-prefix and amateur uses A-prefix in addition to N and K and W). Something like WXX1234 or KA9876. You get the idea. Some very old stations have three-level alphabetical only callsigns (WLO is a good example) and this also applies to US Navy and USCG stations (NMN, NAA, etc).
If the users on 8076 USB are licensed, they should, in theory, be identifying using their FCC-issued callsign. Of course, there's always the chance they simply picked a vacant frequency and used it.
Since you have the day off, I'd put 4724/6739/8992/11175 in your "scanlist". As I said before, most USAF traffic is simulcasted across all frequencies. There are several alternate ("discrete") USAF HF frequencies such as 11180 that also sometimes have USB voice traffic in addition to encrypted digital modes.
There are Portuguese-speaking fishermen chattering away on 6925 kHz LSB right now, and I imagine 6900 LSB and the nearby frequencies will become active after 2300-0000 UTC or thereabouts, if they have any sort of schedule at all.
Since 6707 kHz USB remains a mystery I think your theory about it being a "side channel" to a main net makes sense. You also mention Spanish language activity in the 6-10 MHz range - do you have a listing or log somewhere of the frequencies you've heard that activity on?
Your logs are some of the better ones out there - keep up the good work!
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Postscript:
I just did a quick FCC license search for both 8.076 MHz and 8.0774 MHz. The FCC often licenses USB traffic 1.4 kHz above the "carrier" or "window" (also known as "display" frequency since that's what the radio's display shows). So, for example, 2182 kHz is licensed either as 2.182 MHz, 2.1834 MHz, or in some licenses - like this one:
http://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=1964239 <---click the "Frequencies" tab - using both methods. I then searched for all active licenses with authorization for frequencies 8 to 9 MHz and come up with thousands of results. More research needed.
Here's the Advanced Search page for the FCC website:
http://wireless2.fcc.gov/UlsApp/UlsSearch/searchAdvanced.jspI don't have a lot of time at the moment to browse through all the active licenses for 8-9 MHz (make sure you check "Active" under the "Status" section - or your result will be cluttered with expired/canceled/terminated licenses) but they could be in there. Or they're operating illegally. Still, the FCC license database is a good place to start.