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FM vs SSB



Here is some interesting data for transponder designers. The table compares
the modulation types by the received signal level required for an
articulation index of 30%.

Unprocessed     Processed       RF
PEP     Avg.    PEP    Avg.    PEP     BW     Mod.
39      53      35      42       3      SSB
39      53      35      42       6      DSB
45      45      41      41       6      FM
46      46      42      42      12     FM
54      59      43      48       6      AM
Source: Sabin & Schoenike, "HF Radio Systems and Circuits"

The articulation index is the percentage of spoken words received correctly.
The audio bandwidth in all cases is 300-3000 Hz. Processed speech is
preemphasized by +6dB/octave above 500 Hz to prevent loss of the weaker
high-frequency components in the human voice and then clipped to a 7dB
peak-to-average power ratio. The power levels are in dB above the receiver
IF noise level in one Hz so that they are proportional the power output at
the transmitter regardless of receiver bandwidth..

Note that narrowband FM requires the lowest peak power level. SSB requires
the lowest average power level.

73,

John
KD6OZH



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