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# General RF/Microwave ElectronicsRF Cafe Quiz #3

All RF Cafe Quizzes make great 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. Bonne chance, Viel Glück, がんばろう, buena suerte, удачи, in bocca al lupo, 행운을 빕니다, ádh mór, בהצלחה, lykke til, 祝你好運. Well, you know what I mean: Good luck!

Note: Some material based on books have quoted passages.

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

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