DSC equipment classes

The DSC technical standard defines different classes of VHF DSC equipment:

Class A equipment, which includes all the facilities defined in the international standard to comply with the GMDSS requirements for merchant ships.  Class A DSC equipment uses two antennas - with one dedicated to the DSC receiver.  

Class D equipment, which is specifically designed for recreational vessels. It  provides VHF DSC distress, urgency and safety as well as routine calling and position polling.  Class D equipment includes a dedicated channel 70 DSC receiver, so you will never miss a DSC call.

SC101 equipment.  The SC101 standard was developed in the US some time ago, and was intended to be used in the US domestic market only.

It provides a very limited feature set and omits some very useful options, such as polling.  It has been replaced by the Class D standard.

SC101 equipment has been banned from sale in the US from March 2011.

If you are in the market for a new VHF DSC radio, check very carefully that it is NOT an SC101 model.    

Incoming message alarms

DSC equipment is fitted with specific aural and visual alarms to indicate reception of a DISTRESS or URGENCY priority messages. 

Alarms indicating DISTRESS or URGENCY messages are required to be reset manually, they are not self canceling. 

Dedicated distress button

As discussed earlier, VHF DSC equipment is fitted with a dedicated red DISTRESS or emergency button.  The button requires 'two separate and independent' actions to activate a distress call.  

This usually involves lifting the hinged flap over the button and holding the button down for a short period.

The complete DSC technical specification may be found here.  

VHF DSC ship equipment