> John wrote: > --some want better weak signal performance at the cost > of speed (~HF) > --some want more speed at the cost of signal < performance (~10M & VHF)
Hi John, Fortunately, this choice is already built into the 188-110 system. Here is the specification a 8PSK MIL-STD-188-110 modem meets for minimum performance of Baud vs SNR vs Bit Error Rate in a fading channel. Examples: 4800baud non-fading channel is +17db SNR at 1.0E-3 Bit Error Rate. 75baud fading channel is +2dB SNR at 1.0E-5 Bit Error Rate. Generally speaking, with ARQ on HF, the average SNR to produce a good no-error final output is significantly lower... in other words, it works down into the noise with ARQ, at slower speed when needed. Keep in mind that these are the requirements in the specification. In order to meet these consistently, the equipment needs to be better than the spec. 73---Bonnie KQ6XA =Baud=ChannelPaths=Multipath(ms)=Fading BW(Hz)=SNR(dB)=BER 4800 1 Fixed - - 17db 1.0E-3 4800 2 Fading 2ms 0.5 27db 1.0E-3 2400 1 Fixed - - 10db 1.0E-5 2400 2 Fading 2ms l 18db l.0E-5 2400 2 Fading 2ms 5 30db 1.0E-3 2400 2 Fading 5ms 1 30db 1.0E-5 1200 2 Fading 2ms 1 11db 1.0E-5 600 2 Fading 2ms 1 7db 1.0E-5 300 2 Fading 5ms 5 7db 1.0E-5 150 2 Fading 5ms 5 5db 1.0E-5 75 2 Fading 5ms 5 2db 1.0E-5 NOTES: 1. Fading test per ITU-R F520-2. 2. Both signal and noise powers are measured in a 3-kHz bandwidth.
