This plugin can be used to demodulate DSC (Digital Selective Calling) transmissions, which are short, pre-defined digital messages transmitted by marine radios.
DSC messages are transmitted using FSK with 170Hz separation at 100 baud, as specified by [ITU-R M.493](https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.493-15-201901-I!!PDF-E.pdf]).
DSC messages can be transmitted on a variety of frequencies, but are most commonly found on: 2,187.5kHz, 8,414.5kHz, 16,804.5kHz and 156.525 MHz (VHF Ch. 70).
<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
<h3>4: UDP</h3>
When checked, received messages are forwarded to the specified UDP address (5) and port (6).
<h3>5: UDP address</h3>
IP address of the host to forward received messages to via UDP.
<h3>6: UDP port</h3>
UDP port number to forward received messages to.
<h3>7: Filter</h3>
This drop down displays a list of all columns which can be used for filtering (8).
* Type - MMSI type of the destination of the message (Ship / Coast station).
* Name - The name of ship / station the message is for (From aprs.fi).
* Category - The message category (Safety, Routine, Urgency, Distress).
* From - MMSI of sender of message.
* Country - Country with jurisdiction of the sender of the message.
* Type - MMSI type of the sender of the message (Ship / Coast station).
* Name - The name of ship / station sending the message (From aprs.fi).
* Range (km) - The distance in kilometers from My Position (specified under Preferences > My Position) to the position of the sender of the message, as reported by aprs.fi (usually from AIS data).
* Telecommand 1 - First telecommand (Test / J3E (SSB) telephony and so on).
* Telecommand 2 - Second telecommand.
* RX - RX frequency (Hz) or channel.
* TX - TX frequency (Hz) or channel.
* Position - Position of ship in degrees and minutes.
* Distress Id - MMSI of ship in distress.
* Distress - Nature of distress (Sinking, Collision, Man overboard and so on).
* Number - Telephone number.
* Time - UTC Time.
* Comms - Subsequent communications.
* EOS - End of Signal (Req ACK, ACK, EOS).
* ECC - Indicates if calculated ECC (Error Checking Code) matches received ECC.
* Errors - Number of symbols received with errors (which may have been corrected if ECC is OK)
* Valid - Whether the message is determined to be valid (contains no detected 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.
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.
