This plugin can be used to demodulate Navtex (Navigational Telex) transmissions, which contain marine navigational and meteorological warnings and forecasts.
These are broadcast worldwide on 518kHz (in English for international messages), 490kHz (often in the local language for national messages) and 4209.5kHz.
Navtex messages are transmitted using FSK with 170Hz separation at 100 baud, using [SITOR-B](https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.625-4-201203-I!!PDF-E.pdf]) encoding.
The [Map](../../feature/map/readme.md) feature can display the location of Navtex transmitters, along with their transmission times and frequencies.
<h2>Interface</h2>
The top and bottom bars of the channel window are described [here](../../../sdrgui/channel/readme.md)
<h3>1: Frequency shift from center frequency of reception</h3>
Use the wheels to adjust the frequency shift in Hz from the center frequency of reception. Left click on a digit sets the cursor position at this digit. Right click on a digit sets all digits on the right to zero. This effectively floors value at the digit position. Wheels are moved with the mousewheel while pointing at the wheel or by selecting the wheel with the left mouse click and using the keyboard arrows. Pressing shift simultaneously moves digit by 5 and pressing control moves it by 2.
<h3>2: Channel power</h3>
Average total power in dB relative to a +/- 1.0 amplitude signal received in the pass band.
<h3>3: Level meter in dB</h3>
- top bar (green): average value
- bottom bar (blue green): instantaneous peak value
- tip vertical bar (bright green): peak hold value
Specifies the geographical area in which the receiver is in. This enables the plugin to decode transmitter station identifiers, and display which transmitter the current transmission timeslot is assigned to (5).
Note that with good propagation conditions, it is possible to receive messages from another area, so the station indicated in the message table (17) should be checked against the location given in the recevied message text.
<h3>5: TX</h3>
Displays which transmitter is assigned the current 10 minute timeslot.
<h3>6: Find TX On Map</h3>
If the [Map](../../feature/map/readme.md) feature is open, when clicked, the Map will be centered on the current transmitter (5).
<h3>7: RF Bandwidth</h3>
This specifies the bandwidth of a filter that is applied to the input signal to limit the RF bandwidth.
This drop down displays a list of all stations which messages have been received from. When a station other than "All" is selected, only messages from that station will be displayed in the table.
<h3>12: Message Type Filter</h3>
This drop down displays a list of all message types that have been received. When a type other than "All" is selected, only messages with that type will be displayed in the table.
<h3>13: Start/stop Logging Messages to .csv File</h3>
* Errors - The number of characters that were received with detected errors.
* Error % - The percentage of characters that were received with errors.
* RSSI - Average channel power in dB, while receiving the message.
Right clicking on the header will open a menu allowing you to select which columns are visible, or locate the station in the selected row on the [Map](../../feature/map/readme.md).
To reorder the columns, left click and drag left or right a column header.
Left click on a header to sort the table by the data in that column.
