filters that filter all but the desired signals. However, SDR and multi-carrier NSD (noise spectral density) of the ADC must be lowered, indicating that a better converter may be re- receivers typically have a "wider" front-end bandwidth quired. Although there are means of increasing the and therefore allow many more signals to pass through the full analog signal chain. As a result, it is much easier for maximum input of the converter or reducing the noise floor of the ADC, it is often easier to specify an ADC a strong signal at one frequency to desensitize the desired with better performance or more bits of resolution. signal at another frequency. Since the receiver has a lim- ited noise floor (thermal and other noise sources), the gain can only be reduced to the point that the weakest signal Higher IP3 requirements retains the minimum SNR required for detections. Since Although neither option comes easily, increasing the the design has already been configured for multiple car- fullscale of the converter may have other undesirable riers, it is likely that the gain has been reduced to a mini- consequences. If the input range is increased, then larger mum SO that the largest expected signal will not overdrive signal swings are required to take advantage of this CHAPTER 2.3 Software defined radio increased range. This implies that high signal powers are There are many factors that will reduce both the required. Therefore, in order to keep the intermodu- MDS and the DR. A key point to remember is that, as lation products at the same level, the IP3 specification of shown here, XDS, MDS, and DR are "static" tests and the drive circuitry must also be increased to take full that in reality more than one carrier may share the dy- advantage of the increased signal range, otherwise, what namic range of a multi-carrier receiver. Because of signal dynamic range is gained will be quickly lost to constructive interference, the fullscale power of the increasing intermodulation distortion, most notably converter must be shared b