Hi, I'm trying to identify the main differences between those 2 modes. Could you help me answer my questions below:
- The baud rate difference don't explain alone the time saving in FT4. What else is helping for this? - Is Costas arrays still use for synchronization in FT4? - Does FT8 use 8-FSK or 8-GFSK? - What is the FT8 occupied bandwidth (that containing 99% of transmitted power)? 73, Fred VE2WFB ------------------------------------------------------------------------- FT4 Message formats: 77 information bits, 14-bit cyclic redundancy check (CRC) and 83 parity bits making a 174-bit codeword FEC type: (174,91) low-density parity check code (LDPC) Synchronization: ??? Transmissions duration: 4.48 s, Modulation: 4-GFSK Baud rate: approximately 23.4 baud Tone spacing: 23.4 Hz Occupied bandwidth (that containing 99% of transmitted power): 90 Hz Threshold sensitivity for 50% decoding probability: S/N = -16.4 dB, measured in the standard 2500 Hz reference noise bandwidth. A priori (AP) decoding can push threshold sensitivity down to -18 dB or better. FT8 Message formats: 77 information bits, 14-bit cyclic redundancy check (CRC) and 83 parity bits making a 174-bit codeword FEC type: (174,91) low-density parity check code (LDPC) Synchronization: 7×7 Costas arrays at the beginning, middle, and end of each transmission Transmission duration: 79*1920/12000 = 12.64 s Modulation: 8-FSK (GFSK???) Baud rate: 12000/1920 = 6.25 baud Tone spacing: 6.25 Hz Occupied bandwidth (that containing 99% of transmitted power): ??? 50 Hz ??? Threshold sensitivity for 50% decoding probability: S/N = -21 dB, measured in the standard 2500 Hz reference noise bandwidth.
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