This was posted to the UDXF group regarding reports of a voice reading from "Huckleberry Finn" on 7536u:
RE: [UDXF] Re: [HFmonitors] Re: 7536.0 USB passages from a book being read
These transmissions are used for training of SIGINT operators, mostly by the US Navy, and these broadcasts are most often used during the various Training/Qualification/Certification phases for large battle groups (like a carrier or large-deck amphibious vessel). The Navy trains for all aspects of modern warfare; such as Anti-Air, Anti-Surface, Anti-Submarine, Mine countermeasures, Air/Flight Ops, and yes, SIGINT. The teams deployed within a battle group have to undergo many of the same qualification steps as the rest of the battle group including acquisition, processing/analysis, geolocation (Direction Finding) and reporting. They have been heard using the Harvard sentences, Huckleberry Finn, the Bible, and even some book that was very inflammatory (calling for the destruction of the US by muslim warriors). They often use speakers with accents or will switch from male to female or even switch speakers mid-sentence in an effort to confuse. Also, if there is voice activity, there is likely some simple digital mode (45/50/75bd RTTY, 110b ASCII or SITOR-B) also active once or twice each hour somewhere nearby. In the past, many of these transmissions have come from the vicinity of Mayport/Jacksonville, San Diego and Seattle/Bremerton. They are run by the Afloat Training Groups (ATGs) that are responsible for training and evaluating the battle groups. The station down on 6950/6990 kHz was coming out of the Mayport/Jacksonville area.