NAVTEX receiver

E 0 NAVTEX receiver NAVTEX, the international maritime service that provides navigational and meteorological information via RTTY (radio teletype) on 518 kHz, makes use of FECTOR. This is a system in which the information is transmitted twice, with a particular interval between the first character and the repeat. FECTOR is decoded automati- cally by a microprocessor that is coupled to the ship"s medium wave receiver. It is, of course, not desirable that the decoder is taking up the medium wave receiver continuously. On the other hand, navigational officers, and many amateur radio listeners, do not want to miss one iota of NAVTEX infor- mation. Obviously, a second receiver is the answer, and this can, of course, be coupled to the decoder night and day. Since only one frequency, 518 kHz, and one type of trans- mission, FSK (frequency shift keying), needs to be received, the circuit can be kept quite simple. The circuit is based on a type TCA440. The AGC (automatic gain control) prov...