NAVTEX (NAVigational TEleX), sometimes styled Navtex or NavTex, is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent maritime safety information (MSI) to ships. NAVTEX was developed to provide a low-cost, simple, and automated means of receiving this information aboard ships at sea within approximately 370 km (200 nautical miles) off-shore. There are no user fees associated with receiving NAVTEX broadcasts, as the transmissions are typically transmitted from the National Weather Authority (Italy) or Navy or Coast Guard (as in the US) or national navigation authority (Canada). Where the messages contain weather forecasts, an abbreviated format very similar to the shipping forecast is used. NAVTEX is a component of the International Maritime Organization/International Hydrographic Organization Worldwide Navigation Warning Service (WWNWS). NAVTEX is also a major element of the Global Maritime Distress Safety System (GMDSS). SOLAS Convention mandated certain classes of vessels must carry NAVTEX, beginning August 1, 1993. Technical information NAVTEX transmissions are also called narrow-band direct printing (NBDP). The transmissions are layered on top of SITOR collective B-mode. SITOR-B is a forward error correcting (FEC) broadcast that uses the CCIR 476 character set. NAVTEX messages are transmitted at 100 baud using FSK modulation with a frequency shift of 170 Hz. NAVTEX broadcasts are primarily made on the medium frequencies of 518 kHz and 490 kHz. The international NAVTEX frequency is 518 kHz, and these broadcasts should always be in English. National transmission of NAVTEX, where supported, uses 490 kHz specifically for broadcasts in local languages. NAVTEX Marine Safety Information (MSI) national transmissions also take place on HF at 4209.5 kHz using FEC mode. NAVTEX message format NAVTEX messages are transmitted using binary frequency-shift keying (BFSK) at 100 bit/s and a 170 Hz frequency shift. The characters are encoded using the 7-bit CCIR 476 character set which allows for basic error detection. Forward error correction (FEC) is achieved by repeating each character after a 3 character delay, i.e. ...ABCDE... becomes ...A.B.CADBEC.D.E.... This is the same format as the SITOR-B format. A NAVTEX message is built on SITOR collective B-mode and consists of: a phasing signal of at least ten seconds the four characters "ZCZC" that identify the end of phasing a single space four characters B1, B2, B3 and B4 (see below) a carriage return and a line feed the information the four characters "NNNN" to identify the end