Veo que algunos de vosotros tampoco tenéis claras las principales diferencias entre un equipo clase A y otro clase D.
Os pongo un corta y pega en inglés, que, si tenéis paciencia para leerlo entero, os dará una visión muy completa de qué es eso del DSC y de las diferencias entre la clase A y la D:
Cita:
Both category A and D radios can send and receive digitally encoded distress calls on channel 70, which is reserved exclusively for digital communications. Category A radios, however have two separate receivers, with one constantly tuned to channel 70. Category A radios are therefore more flexible and capable of delivering advanced communication capabilities.
With the press of a button, all DSC equipped VHF radios can send a distress call in digital form on channel 70. The call, sent in much less than one second, includes your unique identification number (MMSI) and if the radio is connected to a GPS or Loran C, the precise location of your boat. The distress call will continue to be sent until it is answered by another station. The station hearing the call will likely call your radio on channel 16 or, in the case of the Coast Guard on 22A and begin the process of bringing you the help you need. Having a highly automatic way of making your need for assistance known has obvious advantages.
Because class A VHF/DSC radios have added capability they are more costly than the Class D versions. The separate, dedicated channel 70 receiver in the Class A radio ensures that it is always ready to receive and respond to both emergency and routine DSC calls, even when it is monitoring any of the normal working channels or weather channels. In addition to the second receiver, most Class A DSC radios are equipped with extensive calling number memory and caller I.D. systems and telephone like keypads that greatly simplify entering the MMSIs and names of frequently called vessels and shore stations.
A Class A VHF/DSC radio makes use of the "Selective" in DSC by calling other DSC radios by their unique MMSI number. These radios usually provide an electronic notepad that stores names and MMSIs for other boats or shore stations. Another station can be called by selecting the name or number from the stored list, choosing the channel number on which you wish to communicate and pressing a button. A digital call containing the MMSI being called, the MMSI of your radio and the channel number on which you wish to communicate is sent on channel 70. The called radio recognizes its MMSI and alerts its operator to the incoming call by emitting a ringing tone. The radio automatically switches to the communication channel chosen by the caller, allowing voice communication to proceed with no further action required of either party. If your MMSI is stored in the called radio's memory the operator will be informed of your identity as in a land-line caller I.D. system. Depending on the particular capability of the radio, it may also provide call waiting alert and log calls received when the radio was unattended. Overall, a Class A DSC radio performs much like a cellular telephone.
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Saludos.