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Re: [Phys-l] Special Relativity



Brian Whatcott, in contrast to voice transmitted as digitally-encoded electromagnetic waves, mentioned that the analog methods of traditional AM and FM radio would have both carrier frequency shift and modulation frequency shift. This is true, but the recipient of the Doppler shifted message could compensate for that shift and listen to an undistorted voice. If the recipient knows the carrier frequency the transmitter is using, and needs to tune her receiver to a different frequency to receive the signal, then she knows the amount of Doppler shift. This means she can stretch or compress the signal back to the correct frequency and then demodulate it. (Or she can demodulate it and expand/shrink the demodulated voice signal by the appropriate amount.)

The method of dealing with the Doppler shift indeed depends on how the voice/music/information is encoded onto the E&M carrier, but no matter what encoding is used, the recipient should be able to compensate for the Doppler shift and end up with undistorted information.

Since all methods of information transmission via E&M waves involves some encoding/decoding process, I would suggest that compensation for a Doppler-shifted carrier should be part of the decoding process. That is, if the recipient is getting "distorted" information, then the transmission wasn't properly decoded.

Michael D. Edmiston, PhD.
Professor of Chemistry and Physics
Chair, Division of Natural and Applied Sciences
Bluffton University
Bluffton, OH 45817
Office 419-358-3270
Cell 419-230-9657