ULB Spec.
Operating Frequency: 37.5 kHz ± 1 kHz
Operating Depth: Surface to 20,000 feet
Pulse Length: Not less than 9 milliseconds
Pulse Repetition Rate: Not less than 0.9 pulse per second.
With two ULBs close to one another, and transmitting, is there not a chance that heterodyning will affect the already very weak signals? Two RF transmitters would certainly be affected - so why not 37Khz?