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EGC std-C decoder

Feature EGC std-C decoder

LES+EGC std-C decoder

full GUI interface Yes Yes
visual quality, volume, sync, locked center frequency Yes Yes
visual signal strength indicator
(useful for peaking antenna)
No Yes
basic channel parameters from bulletin board Yes Yes
good / bad frames counter Yes Yes
user selectable colors for fore and background Yes Yes
FleetNet
SafetyNet

Yes

Yes
Group message decoding Yes Yes
All encoding processing
(ITA2, ASCII, binary)
Yes
NCS
Yes
NCS+LES
NCS file extension assignment based on file header analysis (third party app TrID by Marco Pontello) Yes Yes
possibility to save decoded data to output file Yes Yes
Sound device card input selector Yes Yes
queued messages indicator EGC / LES respectively Yes Yes
list of active LES frequencies sent on NCS No Yes
automatically log RAW data messages for post processing No Yes
LES file extension assignment based on file header analysis (third party app TrID by Marco Pontello) No Yes

FleetNet & SafetyNet graphical map representation
(very neat!)

No Yes
LES channel message decoding! ~7 channels per satellite to explore No Yes
LES channel all encoding processing No Yes
Night mode No Yes
Save sound card input No Yes
Message counter No Yes
Smart autoscroll for Terminal window No Yes
Indicator of Ocean region serviced by satellite No Yes
Depending on the version you will be able to demodulate and process data from the NCS (EGC messages, weather bulletins, navigation information) or the LES channels of non public nature.

Intro

The Enhanced Group Call (EGC) service is a message broadcast service with global coverage (except the poles) within the Inmarsat-C communications system. Two of the services provided are:
  • FleetNET
  • SafetyNET
FleetNET is used to send commercial messages to individuals or groups of subscribers (for example, individual companies communicating with their own Mobile Earth Stations (MES)). SafetyNET is used for broadcasting Maritime Safety Information (MSI) such as navigational warnings, meteorological warnings, meteorological forecasts and other safety related information (including Distress Alert Relays) from official sources.

Requirements if using communications radio:

  • Communications Receiver covering 1550 Mhz in USB mode
  • Parabolic dish and preamplifier or patch antenna for 1550 Mhz
  • Clear view to one of the satellites. For pointing a dish, a rough estimate is given by www.dishpointer.com
  • Suitable audio cable between receiver and PC soundcard.
  • PC with soundcard
  • Java Runtime Engine: JRE v1.8 JDK

Requirements if using SDR

(may vary slightly depending on setup)
  • RTL-SDR USB stick covering 1550 Mhz
  • Parabolic dish and preamplifier or patch antenna for 1550 Mhz
  • Clear view to one of the satellites. For pointing a dish, a rough estimate is given by www.dishpointer.com
  • USB extension cord
  • SDR#
  • Virtual Audio Cable
  • Java Runtime Engine: JRE v1.8 JDK


inmarsat setup

Linux support:

Java means platform independece, so you can run the program even under Linux doing the following:

1. rename the .exe to .jar

2. go to the program directory and run java -jar decoder.jar

Running the program:

Real life examples of the two versions

EGC std-C decoder

LES+EGC std-C decoder 
screendump screendump
click on image for full size

Graphical map representation of EGC messages: ("pro" LES+EGC version only)

You will get a lot of these generated throughout the day when tuned back to the old good NCS channel. And it will make every piece of information jump to life, compared to when receiving it in just plain text!

 
click on image for full size

TODO:

  • interactive frequency slider
  • add spectrum analyzer to incoming audio
  • (send ideas)

Receiving text EGC messages

The program was on purpose written so that it will display only EGC messages in their entirety. This means that if you are evaluating the decoding capabilities with a live or prerecorded EGC, you need to have synchronized, and receive the EGC from the first packet to the last in order for it to be displayed.

Sound Input

The program works by demodulating the sound captured from the audio device. You should make a connection between the receiver and the Line-In of your soundcard using a standard audio cable with a 3.5" male connector on each end.
You should obtain a signal that looks like the image below. The image shows the frequency spectrum of a BPSK signal. Notice that the peak is around 2000 Hz


 



You should have the program's tuner around this frequency!

 

RTL-SDR

It is highly recommended to pass the audio through VAC (Virtual Audio Cable) or any other similar software, but remember to select the appropriate input device from the program's settings menu.
It kind of redirects outputs to inputs to help the program capture the audio that would normally be considered an "output".

Sound Level

The bar turns yellow if the sound is too low. The level should actually be around 30% of the bar and not more! Look at the screenshot!

Reception Mode
EGC

Tune your receiver to the NCS channel for your ocean region. That is ONE channel per Inmarsat C satellite - or per ocean region. The receiver (or RTL stick) should be capable of tuning this frequency in USB mode. Also note that resolution of aproximately 10 Hz is almost a requirement as a stable signal is required for maintaining a constant decoding success rate. The center frequency (cf) is adjustable. Adjust the cf of the modulated BPSK signal to whatever you have set in the config.txt file. By default the cf of 2000 Hz is stored in the file. A limit between 1500 and 3500 Hz has been set. As long as the slider is within +/- 100 Hz of the chosen cf you will have good decoding. Beware that receivers tend to drift in frequency somewhat so slight adjustments will be needed every roughly 30 minutes until the receiver stabilizes on its operating temperature. In order to tune 1541.4500 you might actually have to tune 1541.448 (USB). RTL-SDR stick don't tend to drift in frequency and therefore more recommended for this type of decoding.
 

LES

You have so much more to explore! Select any active LES channel and start receiving messages. Some have more traffic than others, try them all out. Channel with ID 121 on AOR-E has some heavier traffic. Remember to respect the privacy of others!
Below: A table with a list of the currently available channels as sent by the satellite, (live example from AOR-E below).

Links

Useful for getting a first rough estimate, where to point the satellite dish
www.dishpointer.com

Files

If you need more information please contact me on:
{ admin @ tekmanoid.com }.
EGC version

First released in 2009

v0.8.0 

Channel NCS

 

LES+EGC version

First released in 2017

v1.1.35

15 Aug 2017

Channel NCS + LES

Testimonials (Pro version)

"I ran a wave audio file on a continuous loop for over 8 hours and your program is running flawlessly!"
"Excellent results, and software works great"
"Many thanks for your time, it is greatly appreciated!"
"Just wanted to tell you I'm having a great time with your program!"
"Just a thumbs up. The program works really good, and with the spectrum analyzer, I think it'll be excellent."