GB 14391-2021Performance requirements for satellite emergency position indicating radio beacons (English PDF)

3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in GB/T 16162 apply.

3.2 Abbreviations

The following abbreviations apply to this document.

BCH-1: First BCH error-correcting field

BCH-2: Second BCH error-correcting field

C/S: Cospas-Sarsat (international search and rescue satellite system)

EPIRB: Emergency Position Indicating Radio Beacon

GNSS: Global Navigation Satellite System

IMO: International Maritime Organization

PDF-1: First Protected Data Field

PDF-2: Second Protected Data Field

RHCP: Right Hand Circular Polarization

RLS: Return Link Service

VSWR: Voltage Standing-Wave Ratio

4.1 EPIRB functional components

The EPIRB consists of the following two functional components:

a) digital message generator;

b) modulator and 406 MHz transmitter.

4.2 Digital message generator

4.2.1 General

The digital message generator is used to key the modulator and the 406 MHz transmitter so as to transmit the message defined in Clause 5.

4.2.2 Repetition period

The repetition period shall not be fixed; it shall be randomly distributed between 47.5 s and 52.5 s, with a mean interval of 50 s.

4.2.3 Total transmission time

The total transmission time shall be measured at the 90% power points and shall be:

a) for the short-format message: 440 × (1 ± 0.01) ms;

b) for the long-format message: 520 × (1 ± 0.01) ms.

4.2.4 Unmodulated carrier

The initial 160 × (1 ± 0.01) ms of the transmitted signal shall consist of an unmodulated carrier at the transmitter frequency, measured between the 90% power point and the start of modulation.

4.2.5 Digital message

4.2.5.1 Short-format message

The last 280 × (1 + 0.01) ms of the transmitted signal shall contain 112 bits of message code at a bit rate of 400 × (1 + 0.01) bps.

4.2.5.2 Long-format message

The last 360 × (1 + 0.01) ms of the transmitted signal shall contain 144 bits of message code at a bit rate of 400 × (1 + 0.01) bps.

4.2.5.3 Bit synchronization

The bit synchronization code consists of a series of "1"s and shall occupy the first 15 bit positions.

4.2.5.4 Frame synchronization

The frame synchronization code consists of 9 bits and shall occupy bit positions 16 to 24. In normal operating mode, the frame synchronization code shall be 000101111. In self-test mode, the frame synchronization code shall be 011010000.

4.2.5.5 Format flag

Bit 25 is the format flag bit, used to identify the format of the message that follows. A value of "0" indicates a short-format message; a value of "1" indicates a long-format message.

4.2.5.6 Message content

The remaining 87 bits (short-format message) or 119 bits (long-format message) of data content form the message content field; see Clause 5.

4.3 Modulator and 406 MHz transmitter

4.3.1 Transmission frequency

The transmission frequencies currently used by EPIRBs are as follows:

a) 406.025 MHz: the EPIRB carrier frequency is set at 406.025 MHz ± 2 kHz. Within five years, the carrier frequency shall not change by more than +5 kHz or less than -5 kHz.

b) 406.028 MHz: the EPIRB carrier frequency is set at 406.028 MHz ± 1 kHz. Within five years, the carrier frequency shall not change by more than +2 kHz or less than -5 kHz.

c) 406.031 MHz: the EPIRB carrier frequency is set at 406.031 MHz ± 1 kHz. Within five years, the carrier frequency shall not change by more than +2 kHz or less than -5 kHz.

d) 406.037 MHz: the EPIRB carrier frequency is set at 406.037 MHz ± 1 kHz. Within five years, the carrier frequency shall not change by more than +2 kHz or less than -5 kHz.

e) 406.040 MHz: the EPIRB carrier frequency is set at 406.040 MHz ± 1 kHz. Within five years, the carrier frequency shall not change by more than +2 kHz or less than -5 kHz.

4.3.2 Transmission frequency stability

4.3.2.1 Short-term stability of the transmission frequency

The short-term variation of the transmission frequency within 100 ms shall not exceed 2 × 10^-9.

4.3.2.2 Medium-term stability of the transmission frequency

The medium-term stability of the transmission frequency shall be defined by the mean slope of frequency versus time over 15 min and by the residual frequency variation about the mean slope:

a) mean slope variation: shall not exceed 1 × 10^-9 per minute;

b) residual frequency variation: shall not exceed 3 × 10^-9 per minute.

4.3.3 Transmitter power output

The transmitter output power measured into a 50 Omega load shall be between 35 dBm and 39 dBm. At any temperature within the specified operating temperature range, the transmitter shall maintain this power output range throughout 24 h of operation. The rise time of the power output, measured between the 10% and 90% power points, shall be less than 5 ms.

4.3.4 Antenna characteristics

The antenna characteristics are defined for azimuth angles from 0° to 360° and elevation angles from 5° to 60°, and shall comply with the following:

a) pattern: hemispherical;

b) polarization: RHCP or linear;

c) gain: between -3 dBi and 4 dBi over 90% of the above range;

d) antenna VSWR: not exceeding 1.5:1.

4.3.5 Spurious emissions

When measured with a resolution bandwidth of 100 Hz, in-band spurious emissions shall not exceed the levels specified by the signal mask in Figure 1.

Figure 1 - Spurious emission mask for the 406.0 MHz to 406.1 MHz band: relative to the unmodulated carrier output power (0 dBc at the beacon carrier frequency fc), the mask is -20 dBc between fc ± 3 kHz and fc ± 7 kHz, -30 dBc between fc ± 7 kHz and fc ± 12 kHz, -35 dBc between fc ± 12 kHz and fc ± 24 kHz, and -40 dBc beyond fc ± 24 kHz, out to the band edges at 406.0 MHz and 406.1 MHz.

4.3.6 Data encoding

The data are encoded in bi-phase L, as shown in Figure 2. The value of a bit is represented by the change in level (rising/falling) at the half-bit period within the bit length: a negative transition at the half-bit period represents binary "1", and a positive transition at the half-bit period represents binary "0".

Figure 2 - Schematic diagram of bi-phase L data encoding and modulation: the non-return-to-zero data sequence 1 1 1 0 0 1 0 0 0 over successive bit periods, and the corresponding modulated output switching between Phi1 = +1.1 rad and Phi2 = -1.1 rad from an initial 0 rad.

4.3.7 Modulation

4.3.7.1 The transmitted signal uses bi-phase L modulation with a peak phase deviation of ±1.1 rad ± 0.1 rad. Bi-phase L modulation is a form of binary phase-shift keying, but differs from the usual 2PSK modulation at 0° and 180°: bi-phase L modulation is +1.1 rad (63°) and -1.1 rad (-63°) modulation. See Figure 2 for a schematic diagram of the modulation.

4.3.7.2 The rise time (TR) and fall time (TF) of the modulated waveform shall be 150 µs ± 100 µs; see Figure 3.