bandwidth of the ADC output. DsP techniques can now be used to process the digital baseband signal. This approach eliminates the detector and its associated noise and distortion. There is also more flexibility in the dsp because the adC sampling rate can be shifted to tune the exact position of the Af signal within the The obvious problem with this approach is that the adc must now be able to accurately digitize signals which are well outside the dc to f/2 Nyquist bandwidth which most ADCs were designed to handle Special techniques are available however, which can extend the dynamic range of ADCs to include IF frequencies IMPLIFIED DIGITAL RECIEVER USING IF SAMPLING RF SECTION BANDPASS DSP Is?2Af Figure 5.9 Let us consider a typical example, where the IF frequency is 72.5MHz, and the desired signal occupies a bandwidth of 4MHz ( B=4MHz), centered on the IF frequency(see Figure 5.10). We know from the previous discussion that the minimum sampling rate must be greater than SMHz, probably on the order of 10MHz in order to prevent dynamic range limitations due to aliasing If we place the sampling frequency at the lower band-edge of 7OMHz(72.5-2.5), we will definitely recover the aliased component of the signal in the dc to 5MHz baseband. There is however, no need to sample at this high rate, so we may choose any sampling frequency 10MHz or greater which is an integer sub-multiple of 70MHz, i.e., 70-2 35000MHz,70÷3=23.333MHz,70÷4=17.500MHz,70÷5=14.000MHz,70:6 11.667MHz, or 707= 10.000MHz. We will therefore choose the lowest possible sampling rate of 10000MHz(70-7)9 bandwidth of the ADC output. DSP techniques can now be used to process the digital baseband signal. This approach eliminates the detector and its associated noise and distortion. There is also more flexibility in the DSP because the ADC sampling rate can be shifted to tune the exact position of the Df signal within the baseband. The obvious problem with this approach is that the ADC must now be able to accurately digitize signals which are well outside the dc to fs /2 Nyquist bandwidth which most ADCs were designed to handle. Special techniques are available, however, which can extend the dynamic range of ADCs to include IF frequencies. SIMPLIFIED DIGITAL RECIEVER USING IF SAMPLING Figure 5.9 Let us consider a typical example, where the IF frequency is 72.5MHz, and the desired signal occupies a bandwidth of 4MHz (B=4MHz), centered on the IF frequency (see Figure 5.10). We know from the previous discussion that the minimum sampling rate must be greater than 8MHz, probably on the order of 10MHz in order to prevent dynamic range limitations due to aliasing. If we place the sampling frequency at the lower band-edge of 70MHz (72.5–2.5), we will definitely recover the aliased component of the signal in the dc to 5MHz baseband. There is, however, no need to sample at this high rate, so we may choose any sampling frequency 10MHz or greater which is an integer sub-multiple of 70MHz, i.e., 70÷2 = 35.000MHz, 70÷3 = 23.333MHz, 70÷4 = 17.500MHz, 70÷5 = 14.000MHz, 70÷6 = 11.667MHz, or 70÷7 = 10.000MHz. We will therefore choose the lowest possible sampling rate of 10.000MHz (70÷7)