SECTION 2 BROADBAND RF CHARACTERISTICS 2.1 Frequency bands 2.1.1 Use of AMS(R)S bands Note.- Categories of messages, and their relative priorities within the aeronautical mobile (R) service, are given in Volume II, 5.1.8 (Annex 10). These categories and priorities are equally valid for the aeronautical mobile satellite (R) service (see Radio Regulation No. 3651). 2.1.1.1 Every aircraft earth station and ground earth station shall be designed to ensure that messages defined in Volume II, 5.1.8 are not delayed by the transmission and/or reception of other types of messages employing frequencies within the bands stated in 2.1.2 and 2.1.3 or other frequencies to which the station can tune. Message types not defined in Volume II, 5.1.8 shall be terminated if necessary, and without warning, to allow Volume II, 5.1.8 type messages to be transmitted and received. Note.- See ITU Radio Regulations Footnote 729A Article 8. 2.1.2 To-aircraft 2.1.2.1 The aircraft earth station shall be capable of receiving in the frequency band 1 544 to 1 555 MHz. Note.- Use of the band 1 544 to 1 545 MHz by mobile satellite services is limited to distress and safety operations. Specific details of its use for AMS(R)S are pending further study. 2.1.2.2 Recommendation.- The aircraft earth station should be capable of receiving in the frequency band 1 555 to 1 559 MHz. Note.- The band 1 555 to 1 559 MHz may be protected and utilized by some States for national and international AMS(R)S purposes. 2.1.2.3 Recommendation.- The aircraft earth station should also be capable of receiving in the frequency band 1 525 to 1 544 MHz. Note.- The band 1 525 to 1 544 MHz may be used to communicate for purposes of distress and public correspondence with stations of the maritime mobile-satellite service in accordance with No. 3571 of the Radio Regulations. 2.1.3 From-aircraft 2.1.3.1 The aircraft earth station shall be capable of transmitting in the frequency band 1 645.5 to 1 656.5 MHz. Note.- Use of the band 1 645.5 to 1 646.5 MHz by mobile-satellite services is limited to distress and safety operations. Specific details of its use for AMS(R)S are pending further study. 2.1.3.2 Recommendation.- The aircraft earth station should be capable of transmitting in the frequency band 1 656.5 to 1 660.5 MHz.
Ct' 2-2 Note.- The band 1 656.5 to 1 660.5 MHz may be protected and utilized by some States for national and international AMS(R)S purposes. 2.1.3.3 Recommendation.- The aircraft earth station should also be capable of transmitting in the frequency band 1 626.5 to 1 645.5 MHz. Note.- The band 1 626.5 to 1 645.5 MHz may be used to communicate for purposes of distress and public correspondence with stations of the maritime mobile-satellite service in accordance with No. 3571 of the Radio Regulations. 2.1.4 Tuning increments 2.1.4.1 Channels shall be allocated throughout the bands in increments of 2.5 khz, for the to- and from-aircraft transmission path. 2.1.4.2 Channel assignment and tuning of the aircraft earth station shall be achieved under control from the GES. 2.1.5 Channel numbering 2.1.5.1 The channel number (Ct) shall be defined with respect to the centre frequency on the to-aircraft transmission path by the formula: Cf' frequency of transmission(mhz)&1 510.0 0.0025 2.1.5.2 The channel number (Cf) shall be defined with respect to the centre frequency on the from-aircraft transmission path by the formula: frequency of transmission(mhz)&1 611.5 0.0025 2.2 Frequency accuracy 2.2.1 The frequency of transmission from the aircraft earth station, as would be received at the satellite, shall not vary from the commanded channel frequency by more than ±383 Hz. Note.- The frequency of transmissions received by a sub-sonic aircraft should not vary from the nominal channel frequency by more than ±2 khz due to all causes. 2.3 Aircraft earth stations RF characteristics Note.- The following requirements apply over the entire transmit and receive frequency bands. 2.3.1 General antenna characteristics 2.3.1.1 Reference coverage volume. Antenna systems shall be installed to meet specified operational performance requirements for transmitting and receiving over a coverage volume relative to a horizontal line of flight defined to include 360 degrees of azimuth from 5 to 90 degrees in elevation from a horizontal plane.
2-3 2.3.1.1.1 Recommendation.- The recommended coverage volume should provide at least minimum performance over 360 degrees of azimuth from 5 to 90 degrees elevation relative to the horizontal line of flight for all aircraft attitudes of +20/-5 degrees of pitch and of ±25 degrees of roll. 2.3.1.2 Polarization. The polarization shall be right-hand circular for both receiving and transmitting, in accordance with the definition of CCIR Recommendation 573. 2.3.1.3 Antenna switching. Aircraft earth stations that require more than one antenna shall be capable of switching from one antenna to another in the same antenna subsystem so as to introduce a signal interruption of not more than 40 ms. The number of antenna switch-overs shall not exceed one in any 800 ms period, and four in any one minute period. Note.- The following outlines the requirements for high and low gain antennas, only. It does not preclude the future introduction of mid-gain antennas, however, some of the considerations which must be made before such an introduction are described in the guidance material. 2.3.2 Low gain antenna sub-systems 2.3.2.1 Gain-to-noise temperature ratio. Receiving subsystems employing low gain antennas shall achieve a gain-to-noise temperature ratio (G/T) of not less than -26 db/k over not less than 85 per cent of the reference coverage volume defined in 2.3.1.1; and not less than -31 db/k over the remaining 15 per cent of the reference coverage volume. The only exception to this is the region greater than 70 degrees in elevation from the horizontal plane where the G/T may be at least -28 db/k. 2.3.2.2 Axial ratio. The axial ratio shall be less than 6 db for elevation angles of 45 to 90 degrees and less than 20 db for elevation angles of 5 to 45 degrees or the AES antenna shall have sufficient gain to compensate for additional polarization loss in excess of that caused by the axial ratios. 2.3.2.3 Recommendation.- The G/T should be not less than -26 db/k and the axial ratio should be less than 6 db over 100 per cent of the reference coverage volume. 2.3.3 High gain antenna sub-systems 2.3.3.1 Gain-to-noise temperature ratio. Receiving subsystems employing high gain antennas shall achieve a gain-to-noise temperature ratio (G/T) of not less than -13 db/k over not less than 75 per cent of the reference coverage volume and shall be not less than -25 db/k over the remaining 25 per cent of the reference coverage volume defined in 2.3.1.1. 2.3.3.2 Axial ratio. The axial ratio shall be less than 6 db over the 75 per cent of the reference coverage volume referred to in 2.3.3.1 where the G/T must exceed -13 db/k or the AES antenna shall have sufficient gain to compensate for additional polarization loss in excess of that caused by this axial ratio. 2.3.3.3 Recommendation.- The G/T should be not less than -13 db/k and the axial ratio should be less than 6 db over 100 per cent of the reference coverage volume. 2.3.3.4 Discrimination. The antenna gain pattern for both transmit and receive functions shall discriminate by not less than 13 db between the
2-4 directions of wanted and unwanted satellites spaced 45 degrees or greater in longitude. 2.3.3.5 Phase discontinuity. Beam steering transitions between adjacent beam positions of a switched beam antenna shall not cause RF phase transitions greater than 12 degrees in the transmitted signal. Note.- This requirement only applies to individual array performance in the case of multiple array antennas. 2.3.4 Receiver requirements 2.3.4.1 Receiver spurious response performance. The required performance defined in sections 4.2.3 and 4.5.4 shall be achieved when the receiving antenna is illuminated in the direction of maximum gain by a signal at an amplitude of -100 dbw/m 2 at any frequency in the 1 525 to 1 559 MHz band. 2.3.4.2 Receiver linearity. The required performance defined in sections 4.2.3 and 4.5.4 shall be achieved when the receiving antenna is illuminated in the direction of maximum gain by two unmodulated signals each at an amplitude of -103 dbw/m 2 at any frequency in the 1 525 to 1 559 MHz band and separated by 1 MHz. 2.3.4.3 Receiver out-of-band performance. The required performance defined in sections 4.2.3 and 4.5.4 shall be achieved when the receiving antenna is illuminated in the direction of maximum gain by an unmodulated signal at an amplitude of +3 dbw/m 2 at any frequency in the bands 470 to 1 459 MHz and 1 660.5-18 000 MHz; and at amplitudes decreasing linearly in decibels from +3 dbw/m 2 at 1 459 MHz to -72 dbw/m 2 at 1 525 MHz and increasing linearly in decibels from -72 dbw/m 2 at 1 559 MHz to +3 dbw/m 2 at 1 660.5 MHz. 2.3.4.4 Received phase noise. The design of the receiver and the demodulators shall be such as to ensure full compliance with the performance requirements whenever the received signal phase noise characteristic does not exceed the mask defined in Table 2-1.
2-5 2.3.4.5 Capture range. The receiver shall be capable of acquiring and maintaining lock to signals with a frequency offset from nominal of ±2.180 khz minimum. 2.3.4.6 Receiver doppler rate. The receiver shall be capable of acquiring and maintaining performance per section 3.3 with a rate of change of frequency of 30 Hz per second. Table 2-1. Received phase noise mask Offset from carrier (Hz) Phase noise (dbc) 10-34 100-65 1 000-73 3 000-77 10 000-79 35 000-79 1. Phase noise is measured single sideband relative to carrier. 2. The mask shall be defined by drawing straight lines through the above points on a graph which is logarithmic in frequency. Note.- This mask is illustrated in the guidance material. 2.3.5 Transmitter requirements 2.3.5.1 EIRP limits. The maximum EIRP per carrier radiated in any direction shall not exceed the EIRP radiated toward the wanted satellite by more than 5 db. For low-gain antenna operation, the minimum value of EIRP per carrier when the AES is commanded to the maximum setting shall be 13.5 dbw. For high-gain antenna operation, the minimum value of EIRP per carrier when the AES is commanded to the maximum setting shall be 25.5 dbw. For multi-carrier operation, the maximum allowable operating EIRP shall be a level at which total intermodulation product contribution from active sources is within that permitted in section 2.3.5.7 (In-band intermodulation products) and the gain-to-noise temperature ratio is not degraded below that required in sections 2.3.2.1 and 2.3.3.1. 2.3.5.2 EIRP control. The EIRP per carrier in the direction of the wanted satellite shall be adjustable over a range of 15 db in steps of 1 db by command from the GES. 2.3.5.3 Recommendation.- The minimum EIRP of the power control range should be a function of the channel rate and the satellite beam characteristics to minimize the interference potential. 2.3.5.4 Carrier-off level. The total EIRP when all carriers are commanded off shall be less than -41.5 dbw. 2.3.5.5 Log-on EIRP. When logging on to a GES, the EIRP of the AES shall be at least 13.5 dbw and shall not exceed 18.5 dbw.
2-6 2.3.5.6 In-band spurious outputs. When transmitting a carrier at any level up to the maximum power level, the composite radiated spurious and noise output EIRP (excluding intermodulation products) generated by the AES in any direction referenced to a 4 khz band shall not exceed those levels shown in Table 2-2, except for the frequency band on either side of the carrier centre frequency which is described in 3.2.1. Table 2-2. Maximum spurious levels Frequency (MHz) EIRP/4 khz shall be the lesser of 1 626.5 to 1 660.5-55 dbc -37 dbw 2.3.5.7 In-band intermodulation products. For a multicarrier AES, the EIRP of each intermodulation product shall be at least 24 db below the EIRP of each carrier when transmitting two equal carriers with a total EIRP equal to the maximum allowable operating EIRP of the AES in the band 1 626.5 to 1 660.5 MHz. The AES shall not operate above the maximum allowable operating EIRP. 2.3.5.8 Out-of-band EIRP spectral density. The out-of-band EIRP including spurious, harmonics and noise generated by the AES in any direction referenced to a 4 khz band shall not exceed the level shown in Table 2.3. Table 2-3. Maximum out-of-band EIRP levels Frequency (MHz) EIRP/4 khz 0.01 to 1 525-145 dbw 1 525 to 1 559-185 dbw 1 559 to 1 565-117 dbw 1 565 to 1 585-137 dbw 1 585 to 1 626.5-37 dbw 1 660.5 to 1 735-37 dbw 1 735 to 12 000-87 dbw 12 000 to 18 000-52 dbw 2.3.5.9 Phase noise. The phase noise induced on a modulated carrier shall have a power spectral density not exceeding the envelope defined in Table 2-4.
2-7 Table 2-4. Transmitted phase noise mask Offset from carrier (Hz) Phase noise (dbc) 10-40 100-67 500-72 1 100-80 X -80 1. Phase noise is measured single sideband relative to carrier. 2. The mask shall be defined by drawing straight lines through the above points on a graph which is logarithmic in frequency. 3. X is equal to 35 khz or four times the symbol rate, whichever is greater. 4. Where discrete spectral components exist, the sum of the discrete phase noise components and continuous spectral component averaged over a bandwidth of ±10 Hz on either side of the discrete component shall not exceed the phase noise mask. Note.- This mask is illustrated in the guidance material. 2.3.5.10 Transmitter doppler rate. The maximum rate of change of the frequency of the transmitted signal when compensated for aircraft acceleration in the direction of the satellite shall not exceed 15 Hz per second.