How to test NBDP Radio Telex?

NBDP is required for sea area A2 as per SOLAS chapter IV, regulation 9.3.1. The requirement of having NBDP can be fulfilled by providing an additional Inmarsat ship earth station. If the ships don't have NBDP, you may find an additional Sat-C terminal.

Distress and calling. The frequencies 2174.5 kHz, 4177.5 kHz, 6268.0 kHz, 8376.5 kHz, 12520.0 kHz, and 16695.0 kHz may be used for NBDP and data transmissions by coast and ship stations on a simplex basis for distress and safety purposes

ARQ Mode

ARQ mode is used for one-to-one communication. You send information (text) when you are transmitting station when you press the Over key (F9) and you become receiving station. Now can read the message that another station is sending. When the other station presses “Over”, you again become the transmitting station and this process goes on.

FEC Mode

FEC (Forward error correction) mode is for one station to one or many stations type of communication. This mode is used for broadcasting the message. Unlike ARQ mode, FEC is only one way. That is, with FEC we can transmit our message and then end the communication.

With FEC mode; You send the information you wish to send. Once the information is sent, you disconnect the connection. You cannot switch between transmission and receiving mode, so if you want to communicate with another station, you need to choose ARQ mode. But if you just want to transmit your message, you can choose FEC mode.

Options on NBDP screen and what these mean ?

A NBDP screen typically looks like this.

NBDP screen

The options you see on top of the screen are accessed by function keys. I see sometimes the keyboard functions keys marked with these options for ease of use. Even if it is not there, we can always mark it like this.

NBDP Keyboard

Lets see what each of these functions are for

WRU, HR and OVER keys

The literal meaning of the first two terms is

WRU (Function Key F7): who are you ?

HR (Function Key F8): Here is…

This is the way identity is exchanged between the stations interacting with each other.

NBDP screen WRU HR Over

When you are connected with a station and before you start transmitting any telex message, you need to press these two keys. This will send your identity and ask for the identity of another station.

Logically this is similar to how we start any communication. For example, during R/T communication we pronounce the ship's name and call sign. The Over (Function key F9) is used to switch the direction of traffic. The information sending station becomes the information receiving station and vice versa. As two-way communication is only possible in ARQ mode, the Over key is used when communicating in ARQ mode. One station finishes his message, presses “over” and then waits for receiving the message of the other station. The function of this key is similar to saying “over” over a walkie-talkie after we finish our message.


This is the code that you will see when communicating through NBDP. The meaning of this code is “Go ahead”. When you see this code on your screen, this means that now you are at the transmission station and you are ready to send your message. Again this code will appear in ARQ mode.

Methods of sending a message on NBDP, we can either send a message file stored on a floppy or SD card of the NBDP or manually type the message on the keyboard. In ARQ mode, when you are at the transmitting station, you can just start to type the message and it will be received by another station as you type or you can choose the file to send and it will be transmitted to the receiving station.

To choose the file on Furuno NBDP, after exchanging the answer back (WRU, HR)

  • Press the function key F3 then 3 key to open the [File to Send] window

File to send on NBDP furuno

  • Choose the file to send from the list by pressing up/down arrow
  • Press enter to send the file

How to send / Receive a routine message on NBDP?

Now that we know something about NBDP, let us discuss how we can send a routine message to another ship on NBDP. I will show this on the Furuno GMDSS station.

First thing is to know the MMSI number of the other ship and agree on the working frequency. To communicate with another ship, both your station and the station of the other ship need to be on the same frequency and the NBDP station should be active. To make the connection with other ship stations (on Furuno equipment);

Press the function key F3 to open operate menu and set the working frequency by choosing option 9.

Set Frequency on NBDP

After the operating frequency is set, press function key F3 (Operate) and choose the “manual calling” option

Manual Calling on NBDP ARQ

Select the ARQ mode (remember for one-to-one communication we have to use ARQ mode) and then input the ship’s MMSI number in the ID. Press enter. After you hit “Enter” one of these two messages will appear. It will either show

  • Channel busy check, if the frequency is busy. or
  • Connect Send Lock, if the frequency is open for communication

Now if “Connect send Lock” is highlighted on screen, you are all done communicating with the other ship. When you are connected with the other station, it will show the station’s ID and the frequency you are communicating. Exchange answer back by pressing the F7 (WRU) and then F8 (HR) keys and start communicating. As I said earlier when you are done sending your message, press the F9 (over) key to switch the transmission to another ship. When you see GA+? on your screen, it means that the other station has switched the transmission to you and you can again start to transmit your message.

To end the conversation

  • Exchange the answer back by pressing the F7(WRU) and F8 (HR) keys
  • After an exchange of answer back, press the F10 (End) key to disconnect the line.

How to transmit a distress message on NBDP?

The usual way of GMDSS distress communication is

  • Send the DSC alert to all ships and coast stations on an appropriate distress DSC frequency
  • Switch to the corresponding Radio Telephony (RT) frequency and broadcast your distress message starting with Mayday Mayday Mayday

Now when we have transmitted the DSC alert, how does a ship receiving it know where they can listen to your distress call ? This information is right there in the DSC alert message. In the DSC alert message that a ship sends, it needs to mention First is the Mode of communication it will broadcast its message. That is if the message will be broadcasted on RT or NBDP. J3E is the code for RT communication and F1B is for NBDP. The second is the frequency on which the receivers need to switch on. The frequency will be the corresponding frequency on which a DSC alert is received. So now if you want to communicate the distress message on NBDP, the first step will be to let that know to ships and coast stations who would receive your DSC alert by choosing the Telecommand as “F1B” After you have sent the DSC alert, switch to NBDP corresponding frequency.

To transmit your Mayday message,

  • You can either type and save the Mayday message on floppy drive or SD card of NBDP, or
  • You can type directly while transmitting your message

Either way, you have to follow these steps. Press Function key F3 and select manual call. Choose the FEC option. Remember for broadcasting to all the parties we cannot use ARQ mode which is for one-to-one communication. Leave the station ID blank. This is to be entered only if we are sending the message to a particular station. Press enter. If the frequency is clear, you will see Connect Send as highlighted. Now you are ready to either send your message by input to the keyboard or by choosing a pre-typed file. To send the stored message, press function key F3 and then select the “File to send” option. Press enter and your file will be transmitted.

How to receive a distress communication on NBDP?

When you receive a distress DSC alert. Check if the telecommand is J3E or F1B. If it is F1B, you need to be on NBDP to receive the distress message.

To receive the distress message on NBDP, switch to NBDP frequency corresponding to the frequency on which the DSC alert was received.

Press the function key F3 and choose “Manual Reception”.

Manual reception on NBDP

Select FEC mode and press enter key. When a call is detected, Lock will get highlighted. When the line is connected, [Connect] is highlighted. When the receiving of the message is complete, the NBDP connection will automatically cancel. The received message will be stored in the Floppy (or SD card) of the NBDP.

NBDP Self Test procedures

Now that we know how to operate NBDP, testing NBDP should not be an issue. Actually, NBDP does not require much testing. There is a self-test in the equipment that should be done as per the maker guidelines.

Self Test NBDP

Apart from that, it is a good practice to communicate with another ship at least monthly and keep the records.


NBDP is hardly put in use onboard ships. Many ship owners are now preferring to have another set of Sat-C on board rather than having NBDP fitted onboard. In spite of all that, if we have NBDP on board, we must know how to operate it. After all, if it is on board, it is very much a part of the GMDSS station.

NBDP U.S Stations (Admiralty Digital Radio Signals)

Mobile ID: 1090

Honolulu ID: 1099

Point Reyes ID: 1096

Kodiak ID: 1106

Detailed video

Use NBDP to receive NAVTEX message (video)


47 CFR § 80.361 - Frequencies for narrow-band direct-printing (NBDP), radioprinter and data transmissions.

(This article is for informational purposes only.)



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