Question
What sets the minimum detectable signal level for a direct-sampling software defined receiver in the absence of atmospheric or thermal noise?
Answer Options
- A) Sample clock phase noise
- B) Reference voltage level and sample width in bits
- C) Data storage transfer rate
- D) Missing codes and jitter
Correct Answer: B
Explanation
The minimum detectable signal (\text{MDS}) level is the receiver’s ultimate noise floor. In the ideal absence of external thermal or atmospheric noise, the \text{MDS} is determined entirely by the noise generated internally by the Analog-to-Digital Converter (\text{ADC}). This internal noise is primarily digital in nature (quantization noise).
This quantization noise is set by the reference voltage level and the sample width in bits of the \text{ADC}. The sample width (number of bits) determines the number of quantization steps, and the reference voltage determines the voltage span of those steps. These factors define the smallest change in voltage that the \text{ADC} can detect and represent digitally, thus establishing the theoretical digital noise floor of the receiver.
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