| 摘要 |
The present invention is a method and apparatus for signal conditioning which reduces non-linear distortion caused by RF/FM transmitters by lowering the carrier frequency of the modem transmit signal. This is accomplished by lowering the highest frequency in the input signal to the RF/FM transmitter. In one embodiment, modem datapumps are modified so that the optimal modem carrier frequency is utilized for data modulation. The optimal carrier frequency is computed by placing the lowest frequency component in the transmit spectrum at the low band-edge of the RF channel. In other embodiments, a conventional modem transmit spectrum is shifted to the optimal carrier frequency, which is determined by the method described above. Another aspect of the present invention involves the modification of the receiving modem to operate with both conventional land-line modems and the present invention modified-carrier modems used in conjunction with the cellular telephone network. This is accomplished by implementing energy-correlation filters which determine the frequency band over which the received signal energy is distributed.
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