# General RF KnowledgeRF Cafe Quiz #1

All RF Cafe quizzes would make perfect fodder in 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.

Note: Some material based on books have quoted passages.

1. What is the impedance of free space?

a) 50 Ω
b) 120π  Ω
c) 75 Ω

2. What happens to the noise figure of a receiver when a 10 dB attenuator is added at the input?

a) Noise figure increases by 10 dB
b) Noise figure decreases by 10 dB
c) Noise figure doesn't change

3. An RF system has a linear throughput gain of +10 dB and an output 3rd-order intercept point (OIP3) of +30 dBm. What is the input 3rd-order intercept point (IIP3)?

a) +20 dBm
b) +40 dBm
c) +30 dBm

4. Which filter type has the greatest selectivity for a given order (i.e., N=5)?

a) Bessel
b) Chebyshev (ripple=0.1 dB)
c) Butterworth

5. Which mixer spurious product is a 5th-order product?

a) 1*LO + 5*RF
b) 6*LO - 1*RF
c) 3*LO - 2*IF

6. A 2.8 GHz oscillator is phase-locked to a 10 MHz reference oscillator that has a single-sided phase noise of -100 dBc at 1 kHz offset. What is the single-sided phase noise of the 2.8 GHz oscillator at 1 kHz offset?

a) -48.6 dBc
b) -100 dBc
c) -51.1 dBc

7. What is the power of a 2 Vpk-pk sine wave across a 50 ohm load?

a) -20.0 dBm
b) +10.0 dBm
c) +19.0 dBm

8. Which 2-port S-parameter is commonly referred to as "reverse isolation" in an amplifier?

a) S21
b) S22
c) S12

9. What are the minimum and maximum combined VSWR limits at an interface characterized by a 1.25:1 VSWR and a 2.00:1 VSWR?

a) 1.75:1 (min), 2.25:1 (max)
b) 1.60:1 (min), 2.50:1 (max)
c) 0.75:1 (min), 3.25:1 (max)

10. An ideal directional coupler has a directivity of 25 dB and an isolation of 40 dB. What is its coupling value?
a) 65 dB
b) 40 dB
c) 15 dB