What is the dynamic range limitation of a direct sampling SDR versus a superheterodyne SDR?

The dynamic range limitation of a direct sampling SDR versus a superheterodyne SDR arises from the fundamental differences in how each architecture processes the RF signal. A direct sampling SDR digitizes the RF signal directly at the antenna frequency using a high-speed ADC, while a superheterodyne SDR first downconverts the signal to an intermediate frequency (IF) using a mixer and local oscillator before digitizing. The direct sampling SDR's dynamic range is limited by: the ADC's spurious-free dynamic range (SFDR, typically 60-75 dB for ADCs sampling at 1-5 GSPS; this means a weak signal that is 60-75 dB below a strong signal cannot be reliably distinguished from the ADC's spurious products), the ADC's instantaneous noise floor (determined by the number of bits and sample rate; for a 14-bit ADC at 3 GSPS: SNR approximately 68 dB in the full Nyquist bandwidth), and the wideband input (the ADC must handle all signals in the input bandwidth simultaneously, requiring enough dynamic range to accommodate the strongest signal without clipping while still resolving the weakest signal of interest). The superheterodyne SDR's dynamic range advantages include: narrowband IF filtering before the ADC (the mixer and IF filter select only the desired channel, rejecting strong out-of-band signals that would otherwise consume ADC dynamic range; this can improve the effective dynamic range by 20-40 dB), lower ADC sample rate (the IF ADC operates at a lower frequency, where ADCs achieve better SFDR and SNR), and the ability to use AGC before the ADC (automatic gain control adjusts the signal level to use the ADC's full range). However, the superheterodyne has disadvantages: it can process only one channel at a time (or requires multiple parallel receivers for multiple channels), the mixer introduces its own spurious products (mixer spurs limit the receiver's SFDR to 60-80 dB), and the IF filter limits the instantaneous bandwidth.