Operation Manual

3. Decoding of Messages

The FMD can receive, decode and reproduce messages in

legible characters, when transmitted in Morse, RTTY and SITOR-

NEC codes. Apart from these codes there are many other

code types used in radio communication which are ciphered.

These types of messages are not for the general public and

can therefore not be decoded by the FMD55.

Weather, SAR and navigational warnings for shipping are

transmitted in codes, which the FMD55 can decipher.

The reception signal (LF) is fed to the signal processor where the

usable signal tone is filtered out and converted into digital

information.

The mode of the type of code transmitted by a station, can be

found in corresponding maritime radio manuals. Various

abbreviations are used:

xfor MORSE : CW, A1, A1A, telegraphy

xfor RTTY : F1B, radio teletype,

xfor SITOR : FEC, ARQ, F1B

Before a signal can be decoded, it must be reasonably free of

interference, (i.e. with the least possible noise ratio, no clicking

or crackling, no other disturbing stations in the receiving range).

In the top two lines of the LCD display, a signal spectrum is

depicted to assist in the adjustment.

Morse signals consist of only one tone. By reception of an

undisturbed MORSE signal, the following picture appears on the

display