At 11:06 AM 10/1/2006, Lyle Johnson wrote: > >> The theory behind PSK shows that it is indeed far better than CW. > >> > > Begging to differ, but PSK is not "better" than CW, if we are talking > > weak signal detection. > >Just a point of interest: in the NASA deep space network, working with >truly weak signals, PSK is used rather than carrier on-off keying.
Two reasons for this: 1) You're peak power limited, so you want to run at peak power all the time. Why throw away power half the time (when you're key up)? Constant envelope modulations which lend themselves to high efficiency saturated amplifiers are preferred for this reason. Thermal management (which affects stability of the circuits) is also simpler with constant power dissipation. In an average power environment (e.g. a cost limited HF power amplifier with limited heat sink size), the trades are a bit different. 2) Historically, the same signal is used for navigation and communication, and PSK with mod indices such that there's residual carrier is used to make it easy/possible to acquire and track the carrier. But also, be aware that DSN isn't dealing with skywave paths that have significant dispersion. Jim _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
