For those that may be interested, I have been playing with very low power levels lately, as low as -17 dBm or 20 uWatts. Since WSPRnet can only be set to a low power level of 0 dBm, I am using "/" to designate lower levels. IE "/10" for -10 dBm or "/17" for -17 dBm.
So far I've been able to get spotted occasionally at -17 at distances of about 700 - 1000 miles on 20 M. Amazing mode!
John / K5XL