How many SITOR (NBDP) signals can occupy the space of one voice signal?

The capacity to transmit multiple SITOR (Selective Interconnected Telex Over Radio, also referred to as NBDP, or Narrow Band Direct Printing) signals within the same bandwidth as a single voice signal is a key aspect of maritime communications. In this specific case, the correct answer indicates that up to six SITOR signals can fit into the space occupied by one voice signal.

This efficiency stems from the characteristics of Narrow Band Direct Printing, which is designed to transmit data at a lower bandwidth compared to voice transmissions. The modulation techniques and data framing used in SITOR are optimized for efficient use of frequency, allowing for multiple data signals to be transmitted without requiring the full bandwidth that would be necessary for a voice signal.

The available options that suggest fewer or greater numbers would therefore not align with the technical specifications and standards set within the GMDSS framework, where SITOR is utilized effectively for sending distress and operational messages as well as routine communications.