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53 55 30 31 30 36 6A 6E F2 60 12 C5 67 33 FB S U 0 1 0 6 j n .... g 3 . 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ............... 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ............... 00 00 00 00 00 00 00 ....... Preamble 300 bps 1.8 sec Interleaver FREQ ERR 15.059247 Hz Errors 2 [MPDU AIR CRC PASS] Nr LPDUs = 1 Ground station ID SHANNON - IRELAND SYNCHED Aircraft ID AF Slots Requested medium = 0 Low = 0 Max Bit rate 1200 bps U(R) = 0 UR(R)vect = 0 [LPDU UNNUMBERED DATA] [HFNPDU PERFORMANCE] 14:45:30 UTC Flight ID = LH8409 LAT 46 42 34 N LON 21 22 55 E 07 87 AF 00 03 00 31 4D 1D 0D FF D1 4C 48 38 ...... 1 M .... L H 8 34 30 39 73 13 82 34 0F C5 67 01 36 03 02 02 4 0 9 s ..4 ..g .6 ... 00 B6 00 00 00 00 00 00 00 00 03 00 00 00 00 ............... 02 00 00 00 00 00 01 00 00 00 01 01 D3 EA 00 ............... 00 00 00 00 00 00 00 ....... Preamble 300 bps 1.8 sec Interleaver FREQ ERR 8.355845 Hz Errors 0 [MPDU AIR CRC PASS] Nr LPDUs = 1 Ground station ID SHANNON - IRELAND SYNCHED Aircraft ID AD Slots Requested medium = 0 Low = 0 Max Bit rate 1200 bps U(R) = 0 UR(R)vect = 0 [LPDU UNNUMBERED DATA] [HFNPDU PERFORMANCE] 14:43:30 UTC Flight ID = LH8393 LAT 52 37 27 N LON 16 46 41 E 07 87 AD 00 03 00 31 C5 0B 0D FF D1 4C 48 38 ...... 1 ..... L H 8 33 39 33 BF 56 62 EE 0B 89 67 01 8A 07 01 B8 3 9 3 .V b ...g ..... 00 7E 00 00 00 00 00 00 00 06 0F 00 00 00 00 ............... 2E 00 00 00 00 00 05 00 00 00 05 07 08 27 00 ............... 00 00 00 00 00 00 00 .......
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HF communications 79 Figure 5.7 Ground station and aircraft locations for the HFDL communications in Figure 5.6 Figure 5.8 Radio path for LH8409 Figure 5.6 shows typical HFDL messages sent from the four aircraft shown in Figure 5.7 to the Shannon HFDL ground station using the same communications channel. The radio path from one of the aircraft (LH8409) is illustrated in Figure 5.8. The first two of the messages shown in Figure 5.6 are log-on requests and the maximum bit rate is specified in the header. In each log-on request, the aircraft is identified by its unique 24-bit ICAO address . Once logged on, the aircraft is allocated an 8-bit address code (AF hex in the case of the third message and AD hex in the case of the fourth message). Each aircraft also transmits its current location data (longitude and latitude). The system used for HFDL data exchange is specified in ARINC 635. Each ground station transmits a frame called a ‘squitter’ every 32 seconds. The squitter frame informs aircraft of the system status, provides a timing reference and provides protocol control. Each ground station has a time offset for its squitters . This allows aircraft to jump between ground stations finding the best one before logging on. When passing traffic, dedicated TDM time slots are used. This prevents two aircraft transmitting at the same time causing data collisions .
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80 Aircraft communications and navigation systems Figure 5.9 A simple SSB transmitter/receiver The block schematic of a simple HF transmitter/ receiver is shown in Figure 5.9. Note that, whilst this equipment uses a single intermediate frequency (IF), in practice most modern aircraft HF radios are much more complex and use two or three intermediate frequencies.
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  • Spring '10
  • MrLEE
  • Frequency, ........., Single-sideband modulation, HF radio

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