So what happens if you set your RF bandwidth to 171 kHz (10% of 1710 kHz), then brick-wall lowpass your audio chain above, for example, 8 kHz, like some IBOC stations do (but without running the IBOC)? (Also maybe you run IBOC-like sidebands at -4.5 dB modulation at 150 kHz off center frequency.) Would you be able to do 100 µV/m @ 30 meters then?
Some short answers:
Even a field of 100 µV/m would not provide an acceptable S/N for a typical AM receive setup over a free-space path of 30 meters.
Also, speaking of a higher frequency (mentioned in 15.225 (a)) like 13.56 MHz, is it possible to use an electrically short antenna (1° or shorter) in a portable device resting on a table/podium/etc, and have radiation that primarily uses the skywave (like shortwave) or direct wave (like FM)? (For FM I can understand if it'd help to mount the antenna higher if possible, but for me much of the time that would be impractical as my feet would still be in firm contact with the ground when I set it up.) Also how would you calculate the power required with such a short un-grounded (unless the chassis of the device counts) antenna to meet the field strength requirement? (There are other situations I would like to figure out as well, so rather than telling me "you have to run 500 milliwatts with a 0.01° antenna at 1710 kHz" or "if you want to run 50 watts you must use an antenna shorter than 0.0001°" or whatever it is, I'd like to learn how to calculate it myself if possible.)
I admire the interest you show in learning about these subjects, but this isn't the best venue to do that.
Suggest you get a copy of Radio Engineers' Handbook
by F.E Terman, which has comprehensive chapters on antennas and the propagation of radio waves. Reference Data For Reference Engineers
is another good resource. I think both can be ordered on line from various sources.
The Terman work is readable (and downloadable) on line at http://www.scribd.com/doc/23847007/Radio-Engineers-Handbook-1943-Terman