The VHF EPIRB DSC distress alerting
signal should be transmitted on the frequency of 156.525 MHz using
G2B class of emission.
The frequency tolerance should
not exceed 10 parts per million.
The necessary bandwidth should
be less than 16 kHz.
The output power should be at least
The emission should be vertically
polarized at the source.
6.1 Frequency modulation with a pre-emphasis characteristic
of 6 dB/octave (phase modulation) with the modulating sub-carrier,
should be used.
6.2 A sub-carrier of 1,700 Hz with frequency shift
between 1,300 Hz and 2,100 Hz should be used.
6.3 The frequency tolerance of 1,300 Hz and 2,100
Hz tones should be within ± 10 Hz.
6.4 The modulation rate should be 1,200 bauds.
6.5 The index of modulation should be 2.0 ±
DSC Message Format and Transmission
7.1 The technical characteristics for the DSC
message should be in accordance with the sequence for the "distress
call" specified in Recommendation ITU-R M.493.
7.2 The "nature of distress" indication should
be "EPIRB emission".
7.3 The "distress co-ordinates" and "time" information
need not be included. In this case the digit 9 repeated 10 times and
the digit 8 repeated four times should be included as specified in
Recommendation ITU-R M.493.
7.4 The "type of subsequent communication" indication
should be "no information" (symbol # 126) which indicates that no
subsequent communications will follow.
7.5 The alerting signals should be transmitted
in bursts. The (N+1) burst of transmission which consists
of five successive DSC sequences should be made with an interval of
Tn after the Nth burst as given in Figure 1.
Figure 1 Alerting Signals