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Jerry — There are 2 Part 15 “shortwave” bands:
1. A band 14 kHz wide and centered on 13.56 MHz. This is wide enough for one AM broadcast-quality signal (audio up to 7 kHz, so actually better), or two SSB signals with the same audio.
2. A band from 26.96 MHz to 27.28 MHz.
The limit in each band is signal strength. There is no “alternate” standard for limits in terms of input power, antenna length, etc. The 13.56 band has a much greater strength limit (15,848 uV/m at 30 meters) than the higher band (10,000 uV/m at 3 meters).
There’s a topic on “Part 15 shortwave” currently on the second page (older topics) of the topic list. We (yours truly included) hashed over some things.
If you look at the current Page 2 of the Stations by Frequency list, 1570 WBDH started testing a Part 15 AM transmitter on 13.56 MHz. Unfortunately, their Web site has no updates on the tests.
Shameless Plug: This is also covered in the “Digest of Part 15” in the Library.