What is MTM, Text messages?

—Under devolopement—
Following topic is still under developement and will work in the future on your easyTRX3 unit.

Please note that only SOTMA units are able to send Binary Broadcast messages and it is not sure that the boat owners read that message although
the SOTMA unit automatically acknowledged the reception!

The easyTRX3 is a AIS Class B SOTDMA unit.
This SOTDMA allows Class B unit as same as Class A to send text messages over AIS.

We call that MTM, Maritime Text Messenger.
Therefore we have a special App which connects to your easyTRX3 mit WiFi (WiFi within TRX3 is required).
If you don´t have a easyTRX3 with WiFi you could use USB for PC/MAC.
WiFi-App for Android: https://play.google.com/store/apps/details?id=com.weatherdock.easyTRX3Msg
WiFi-App for iOs: not available

Adressed Message:
AIS message 6 & 26 are used for that adressed Message and will be send to a specific MMSI number.
If you want to send a message to an MMSI number its necessary that this boat is also equipped with a SOTDMA unit.
Then the reception will automatically be acknowledged by it.
Note that this still does not mean that the boat owner was read that message!
One message could contain up to 48 symbols.
Within a minute you could send in total 72 symbols.
“Arrival in Marina Portofino, ETA 1800”

Broadcast message:
For that AIS message 8/26 is used to send an all ships message to all AIS units within range.
Here you could use up to 54 symbols.
Within one minute you are allowed to send 72 symbols.
“Marina Portofino is closed”

How long could your record with the easyTRX3?

The easyTRX3 has a non removeable integrated SD card.

All received AIS targets and the own position is saved.

By USB you can read-out the SD card.

To do that, please first connect the unit with the programming tool and activate that mode.

Please note that within that time, there is no recording of AIS targets and own position.

For more details please have a look into the manual or follow the instructions within the programming tool.


We are using a 4 or 8 GB micro SD card.

With an AIS traffic of e.g. 20% you can safe up to 2 or 4 months.

Rule of thumb: 2GB per month on an AIS traffic with 20%

Exact calculation:

On an AIS traffic with 20%: 20% x 75 slots/sec = 15 Messages per sec.

Each message has 50 characters -> 15 x 50 = 750 characters.

In additon the RMC (own position) is saved which has 66 characters -> 750 + 66 = 816 characters per second

One month has 2.592.000 seconds -> 2.592.000 x 816 characters = -> 2GB


AIS Know-How: Data transfer (SOTDMA vs. CSTDMA)

Since the end of 2000, the Automatic Identification System (AIS) has become a binding standard to improve the navigation and safety at sea. Position, course, speed, and other ship data are transmitted alternately on the two maritime VHF channels 161.975 MHz and 162.025 MHz. Per minute there are 2,250 Slots available for the transmission of AIS data telegrams.

Two methods are available for transmitting the AIS data telegrams.
On the one hand, the CSTDMA (Carrier Sense Time-Division Multiple Access) method, which is used primarily for pleasure boating (Class B). The CSTDMA method uses carrier-sensing to defer transmissions until no other stations are transmitting. If a free slot is found, the transmission starts. Than the transmission is stopped for a 30 second time interval before the next one starts.
On the other hand, there is the SOTDMA (Self-Organized Time-Division Multiple Access) technology, which was used only by commercial vessels (Class A) but is now also authorized for pleasure boating at Class B level. With the SOTDMA method only the first free slot for the transmission has to be found
. The next five slots are always reserved automatically.

The following hierarchy results for the transmission of AIS data telegrams:

  1. Class A (commercial vessels) & SART (rescue transmitter)
  2. Class B SOTDMA (pleasure boating)
  3. Class B CSTDMA (pleasure boating)


The main advantages of the SOTDMA compared to the CSTDMA technology for pleasure boating (Class B) at a glace:

For more safety at sea - switch to SOTDMA Class B technology now!


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