Furuno DP-6 manual FEC Mode B-Mode, Initiating a Call

1.4 FEC Mode (B-Mode)

Description

The FEC mode is for one-way, uninterrupted transmission of mes- sages, for example, weather forecasts and emergency bulletins, to no one particular station or stations. The sending station is known as the BSS (B-Mode Sending Station), the receiving station the BRS (B-Mode Receiving Station).

This mode uses a simple forward-error correcting (FEC) technique of sending each character twice at a 280 ms interval. The first trans- mission is termed DX (direct transmission), the second RX (re- peated transmission).

Message: " a b c

d

e

f

g

h

i

j "

First transmission:

a

b

c

d

e

f

g

h

i

j

Second transmission:

a

b

c

d

e

f

g

h

i

j

280 ms

Output code ex.:

a

b

c

a d

b e

c

f d

g

e

h

f

i g j h i j

Figure 1-3 FEC mode transmission technique

The receiving station tests the DX and RX characters for adher- ence to the 4-mark/3-space constant ratio, and prints only unmutilated DX or RX characters, or prints a space if both are mutilated.

Another version of the FEC mode is the FEC-selective mode. This mode uses a call code for selective calling to one or more stations. Only those stations with the correct code will receive the data cor- rectly.

Initiating a Call

When a BSS initiates a broadcast call it transmits synchronizing signals to align phasing of the BRS. Upon detection of this signal the BRS’s are switched to the receiving condition and will remain in this condition until the completion of the message. If the muti- lated character error rate exceeds a certain percentage, the BRS reverts to standby condition.

Termination of Communication

The sending station sends three consecutive idle signals α imme- diately after the last transmitted information signal in the DX posi- tion.

1-4