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General RF/Microwave Electronics
RF Cafe Quiz #3

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All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job.

Some of these books used in quizzes are available as prizes in the monthly RF Cafe Giveaway.

Note: Many answers contain passages quoted in whole or in part from the text.

 

 

1. What is a primary advantage to using 90° (quadrature) hybrid couplers in amplifier designs?

a) Wider bandwidth possible
b) Low noise figure
c) Input/output impedance not dependent on devices as long as device impedances are equal

 

 


2. Why is there a frequency term in the equation for free-space path loss?

a) There is no frequency term
b) Atmospheric absorption
c) Antenna geometry requires it

 

 


3. If an amplifier has a noise temperature of 60K, what is its noise figure for an ambient
    temperature of 290K?

a) 8.0 dB
b) 80 dB
c) 0.82 dB

 

 


4. What is a primary advantage of offset-quadrature-phase-shift-keying (OQPSK)
    over standard QPSK?

a) Greater data rates possible
b) Greater spectral efficiency
c) More constant envelope power

 

 


5. A mixer has the following input frequencies:  RF = 800 MHz, LO = 870 MHz. The desired output
   frequency is 70 MHz. What is the image frequency?

a) 940 MHz
b) 1670 MHz
c) 140 MHz

 

 


6. What is the spurious-free dynamic range of a system with IP3 = +30 dBm and a minimum
    discernible signal (MDS) level of -90 dBm?

a) 80 dB
b) 120 dB
c) 60 dB

 

 


7. A spectrum analyzer displays a component at 10 MHz @ 0 dBm, 30 MHz @ -10 dBm, 50 MHz @ -14 dBm, 70 MHz @ -17 dBm, and all of the other odd harmonics until they disappear into the noise. What was the most likely input signal that caused the spectrum?

a) A 10 MHz square wave (0 Vdc bias)
b) A 10 MHz triangle wave (0 Vdc bias)
c) A 10 MHz cosine wave (0 Vdc bias)

 

 


8. On which side of a rectangular waveguide is an E-bend made?

a) The long dimension
b) The short dimension
c) The inside

 

 


9. During a network analyzer calibration, why are both a short circuit and an open circuit used?

a) They average to 50 ohms in an RF system
b) To determine the characteristic impedance of the measurement system
c) Both are easy to produce to at high accuracy

 

 


10. What is the first harmonic of 1 GHz?

a) 1 GHz
b) 2 GHz
c) 10 GHz

 

 

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