Cuban NDBs seem to have very low effective radiated power - the
signal of 'URV' was received in about
30km distance with the same signal strength as 'CBC'
from the Cayman Islands - a distance of 400 km. 'DDP'
from Puerto Rico, known as a powerhouse, got a 7dB stronger signal
than 'URV', from a distance of 1600 km...
All the other cuban stations also had a low signal level.