E4C Receiver performance: phase noise, noise floor, image rejection, minimum detectable signal (MDS), increasing signal-to-noise ratio and dynamic range, noise figure, reciprocal mixing; selectivity; SDR non-linearity; use of attenuators at low frequencies

- [[E4C01]] (D)
What is an effect of excessive phase noise in an SDR receiver’s master clock oscillator? #card
	- [[A.]] It limits the receiver’s ability to receive strong signals
	- [[B.]] It can affect the receiver’s frequency calibration
	- [[C.]] It decreases the receiver’s third-order intercept point
	- [[D.]] It can combine with strong signals on nearby frequencies to generate interference
- [[E4C02]] (A)
Which of the following receiver circuits can be effective in eliminating interference from strong out-of-band signals? #card
	- [[A.]] A front-end filter or preselector
	- [[B.]] A narrow IF filter
	- [[C.]] A notch filter
	- [[D.]] A properly adjusted product detector
- [[E4C03]] (C)
What is the term for the suppression in an FM receiver of one signal by another stronger signal on the same frequency? #card
	- [[A.]] Desensitization
	- [[B.]] Cross-modulation interference
	- [[C.]] Capture effect
	- [[D.]] Frequency discrimination
- [[E4C04]] (D)
What is the noise figure of a receiver? #card
	- [[A.]] The ratio of atmospheric noise to phase noise
	- [[B.]] The ratio of the noise bandwidth in hertz to the theoretical bandwidth of a resistive network
	- [[C.]] The ratio in dB of the noise generated in the receiver to atmospheric noise
	- [[D.]] The ratio in dB of the noise generated by the receiver to the theoretical minimum noise
- [[E4C05]] (B)
What does a receiver noise floor of -174 dBm represent? #card
	- [[A.]] The receiver noise is 6 dB above the theoretical minimum
	- [[B.]] The theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
	- [[C.]] The noise figure of a 1 Hz bandwidth receiver
	- [[D.]] The receiver noise is 3 dB above theoretical minimum
- [[E4C06]] (D)
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor? #card
	- [[A.]] 3 dB
	- [[B.]] 5 dB
	- [[C.]] 10 dB
	- [[D.]] 13 dB
- [[E4C07]] (B)
What does the MDS of a receiver represent? #card
	- [[A.]] The meter display sensitivity
	- [[B.]] The minimum discernible signal
	- [[C.]] The modulation distortion specification
	- [[D.]] The maximum detectable spectrum
- [[E4C08]] (D)
An SDR receiver is overloaded when input signals exceed what level? #card
	- [[A.]] One-half of the maximum sample rate
	- [[B.]] One-half of the maximum sampling buffer size
	- [[C.]] The maximum count value of the analog-to-digital converter
	- [[D.]] The reference voltage of the analog-to-digital converter
- [[E4C09]] (C)
Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF communications receiver? #card
	- [[A.]] Fewer components in the receiver
	- [[B.]] Reduced drift
	- [[C.]] Easier for front-end circuitry to eliminate image responses
	- [[D.]] Improved receiver noise figure
- [[E4C10]] (C)
What is an advantage of having a variety of receiver bandwidths from which to select? #card
	- [[A.]] The noise figure of the RF amplifier can be adjusted to match the modulation type, thus increasing receiver sensitivity 
	- [[B.]] Receiver power consumption can be reduced when wider bandwidth is not required
	- [[C.]] Receive bandwidth can be set to match the modulation bandwidth, maximizing signal-to-noise ratio and minimizing interference
	- [[D.]] Multiple frequencies can be received simultaneously if desired
- [[E4C11]] (D)
Why does input attenuation reduce receiver overload on the lower frequency HF bands with little or no impact on signal-to-noise ratio? #card
	- [[A.]] The attenuator has a low-pass filter to increase the strength of lower frequency signals
	- [[B.]] The attenuator has a noise filter to suppress interference
	- [[C.]] Signals are attenuated separately from the noise
	- [[D.]] Atmospheric noise is generally greater than internally generated noise even after attenuation
- [[E4C12]] (C)
How does a narrow-band roofing filter affect receiver performance? #card
	- [[A.]] It improves sensitivity by reducing front-end noise
	- [[B.]] It improves intelligibility by using low Q circuitry to reduce ringing
	- [[C.]] It improves blocking dynamic range by attenuating strong signals near the receive frequency
	- [[D.]] All these choices are correct
- [[E4C13]] (D)
What is reciprocal mixing? #card
	- [[A.]] Two out-of-band signals mixing to generate an in-band spurious signal
	- [[B.]] In-phase signals cancelling in a mixer resulting in loss of receiver sensitivity
	- [[C.]] Two digital signals combining from alternate time slots
	- [[D.]] Local oscillator phase noise mixing with adjacent strong signals to create interference to desired signals
- [[E4C14]] (C)
What is the purpose of the receiver IF Shift control? #card
	- [[A.]] To permit listening on a different frequency from the transmitting frequency
	- [[B.]] To change frequency rapidly
	- [[C.]] To reduce interference from stations transmitting on adjacent frequencies
	- [[D.]] To tune in stations slightly off frequency without changing the transmit frequency