Spectral Shaping Without Subcarriers

Abstract

For proper operation of the phase lock loop which tracks a carrier it is important to minimize the spectral energy at frequencies near the carrier. A traditional method is to modulate the data onto a subcarrier in such a way that there is little energy near D.C. The resulting signal then is used to modulate the carrier. The problem with such a scheme is that the total bandwidth is much larger than necessary to transmit the data. This paper proposes and analyzes a simpler scheme which increases the data bandwidth by a very small fraction, yet reduces the energy near D.C. to nearly zero.