What’s the difference between “Simplex” and “Duplex” transmissions?
Most modern day VHF Marine Radios offer the basic transmit and receive capabilities. One way they can communicate is where communication can take place in only one direction at at time. This is called “Simplex” transmission. On each of the radios, there is a button on the side of the microphone which determines whether the user is transmitting or receiving a communication. You press the button to transmit or release the button to receive a communication. “Duplex” transmissions (where communication can take place in both directions simultaneously) is, however, available on the majority of channels. Each duplex channel has two frequency assignments. The history behind this indicates that in the days before mobile phones and satcomms became widespread, the duplex channels could be used to place calls on the public telephone system for a fee via a marine operator. So you see, we’ve come a long way in improving our communication possibilities when on the water. History was never my favorite subject in school, but when you come across some of these interesting facts, and you realize that all this happened within your own lifetime, it really hits home. Let’s enjoy (and appreciate) those simple marine radios we take for granted! Happy Boater.