El nou mode digital T10
Mode digital JT10 anomenat T10 del programa JTDX desenvopulat per UA3DJY (Igor)
JT10 mode is derived from the JT9 mode and has 10 tones where two of them dedicated to synchronization pattern, rest 8 are the message data. Each tone being transmitted for 6912/12000 = 0.576 second, minimal distance between the two neighbouring tones is 4*12000/6912 = 6.94(4) Hz. Frequency bin width is 12000/6912 = 1.736(1) Hz., so there is always a gap between the two neighbouring tones. Whole spectrum occupies 6.94(4)*9 + 1.74 = around 65 Hz. Fano decoder is used for JT10 mode. 16 tones (8+8) are used for SYNC pattern, 69 tones allocated to the message data, total 85 tones being transmitted per 85*0.576= 48.96 seconds time interval.
There are several ideas behind this approach:
– Usage of two tones for SYNC pattern can simplify to distinguish harmonic based signals (JT10b and JT10c), also these QRM-ing signals can be decoded and subtracted from the whole signal in the future SW versions.
– Wider tone spacing shall bring better resistance to the Doppler frequency spreading in comparison to JT65a mode.
– Wider tone spacing shall bring better spectra overlapping capacity in comparison to JT65a mode, and more signal density on the band if signal subtraction is used in the software.
– Relatively narrow bandwidth of JT10 signal will allow to get better band capacity in comparison to the JT65a mode.
So far it is not clear if JT10 will go to the public use, one of the reasons that can stop it’s usage is the relatively small SYNC pattern, and there is a long way ahead to make it more attractive one in comparison to the JT65a mode.
Nota publicada per UA3DJY, desenvolupador del programa JTDX el 17 d’abril de 2017.