Online Help for BlueNavtex2

BlueNavtex2 is a bluetooth user interface for the BT3 Navtex receiver manufactured by Nasa Marine Ltd.


Navtex is an international world-wide system of Medium-band transmitters providing local weather and navigation information. Functionally, the world is split into 21 "NavAreas". Each area allocates a prefix letter to its transmitting stations per frequency. Messages have a prefix which defines the transmitting station, the message type, and a 2-character sequence number. Transmit times (10-minute blocks) are defined by the IMO according to the station prefix letter. All Navtex times are quoted as UTC. Channel A stations (518KHz) transmit in English, Channel B stations (490KHz) transmit in local language.   You can download an app with Navtex data from the developer's website. Note that radio waves cross NavArea boundaries and therefore transmission station codes are NOT unique in "busy" areas.


About the Nasa Marine BT3:

The BT3 receiver receives Navtex messages on either 518 or 490KHz, and you can schedule it to switch beween them to give 1 or 2 sessions of each per day. It can be set to remove duplicate messages (something like 50% of messages are duplicates). The BT3 supports a 4-character user definable PIN to prevent anyone without access to the BT3 device itself from changing personalised settings. You can personalise the BT3 with an 8-character name. Messages are stored chronologically. When the message store (typically several days-worth) is full,  new messages displaces the oldest. The BT3 does not sort, filter or selectively receive messages, but sorting and filtering is carried out by the app. You can issue a CLEAR command to the BT3, which removes most of the stored messages but not the dozen or so newest ones. The BT3 runs 24/7.

About the App:

The BlueNavtex2 app connects to the BT3 device via a BTLE (bluetooth low-energy link) and allows you to control the user functions of the device, and access the stored Navtex messages. When you ask for "all messages" or "my messages" (your personalised list) the app displays an index of the stored message headers and allows you to fetch and view the message content.

Things to note:

1.    BTLE does not "pair" like conventional bluetooth, and you should not attempt to do so from the system menus of your Android device.

2.    Stay within range of the BT3 if connected when using the app, and shut it down when you have finished!


   On first use, the welcome screen and permissions dialogue will activate. Depending on your Android level, you will need to grant some or all of LOCATION, SCAN and CONNECT permissions. Return out of the welcome screen.

1.    Check the BT3 is powered up, and connected to the antenna.

2.    Open the app if not open and read the help files!

3.    Check you are in adequate range of the BT3.

4.    SCAN for the device. The default name of the device is BTnavtex. Select this device.

5.    The device should connect, and a "synchronized" message should show briefly.The "Device Response" box should show the device name, time (UTC) and the current settings for the device.

6.     If it is all connected properly, the "all messages" and "my messages" boxes will be active. "My messages" will not be defined at this stage, so touch "all messages". A message header index will be displayed on the screen. This will be test messages from the manufacturing process, plus anything else the BT3 has received. DO NOT SELECT CLEAR FROM THE SETTINGS UNTIL YOU ARE HAPPY THE SYSTEM WORKS.

7.     Select a message header. The message body should be displayed.

8.    If the steps above are successful, the BT3 is running and communicating with the app. Give the BT3 time to receive some messages, then you are good to go!

9.    If you are happy that you can access and view messages from the BT3 receiver, you can personalise the BT3 to the app, and use the various settings.

NOTE: Always close the app when you are finished to disconnect the link to the BT3 !



With the BT3 connected, you can access the settings menu from the task bar. It is recommended that you set a PIN and personalise the BT3 name first. Both these need access to the BT3 unit itself. You can check the status of the various settings using "Display Device Settings".

1.    PIN:  From the "Security and Customisation" screen enter a 4 character PIN of your choice (numbers or letters) and SUBMIT. Press the button on the BT3 within 15 seconds and the device will respond with the new PIN.

2.    BOAT NAME: From the "Security and Customisation" screen enter an 8 character name for your BT3. Almost anything is acceptable, upper/lower case, numbers or symbols. Close the app and de-power the BT3 briefly. When you SCAN next time the new name will be automatically selected from the list and will connect. You can disable this functionality with the "Auto Connection" menu item if you wish.

3.    CHANNEL: The "Lock Channel" item will switch the BT3 receiver between channel A and B.

4.    CHANNEL TIMERS:  The BT3 can switch between the the two channels once or twice  a day. Set this up on the screen and submit. Turn the switching function on or off as required.  Example

5.    CLEAR:  You can clear all but the newest 20 messages.

6:    REPEATED MESSAGES:  Many ( about half) are duplicated. You can hide these.

7.    FILTER MESSAGES:  You can set your preferred stations and message types in "Set my Messges". Up to 6 A or B stations, and up to 6 message types. it is recommended that you always have message type D (SOS) included in your list.  Example



You can view all messages or your preferred ones ("my messages").  The messages are indexed at the left-hand side of the screen, and arranged newest at the top. Choose the required messge and click on it to view the message contents. "SORT" arranges the message index alphabetically, and LOCK stops your device from flipping between portrait and landscape mode