1
The VHF EPIRB DSC distress alerting
signal should be transmitted on the frequency of 156.525 MHz using
G2B class of emission.
2
The frequency tolerance should
not exceed 10 parts per million.
3
The necessary bandwidth should
be less than 16 kHz.
4
The output power should be at least
100 mW.
5
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 ±
10%.
7
DSC Message Format and Transmission
Sequence
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.
and
Figure 1 Alerting Signals