At the end of the transmission a stop tone is sent that switches the receiving unit back to standby mode. For examples take a look at the Weekly Picture page Weather Charts have only Black and White contours, for good resolution 2 Bit decoding is the best way for clear charts 2. To receive these grey scale pictures you should decode them with 8 Bit greyscale. See also the Weekly Picture page For Satellite rebroadcasts the standard RPM is 120 and IOC 576. Synopsis Data on short wave from weather stations around the globe.
All necessary information is contained in each transmission.
The power of each transmitter is regulated so as to avoid the possibility of interference between transmissions. It is used to identify the broadcasts which are to be accepted by the receiver and those which are to be rejected. The subject indicator character is used by the receiver to identify different classes of messages. Navtex broadcasts are all in English on SSB on 518 kHz. What's the best you can do to receive a message and what do you need for receiving it.