OK, I'm no sonobuoy expert but looking up DIFAR Sonobuoy Uplink on Google reveals an uplink data rate of 1200 bits per second; Full Motion Video from a RPAS currently in service is between 1000000 to 3000000 bits per second. Therefore, you could fit over 1000 digitally multiplexed sonobuoys on a single frequency within the same bandwidth of a 1st generation Predator!
The bandwidth argument doesn't stack up...