RF Electronics BasicsRF Cafe Quiz #69

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.

This RF Electronics Basics quiz targets those of you who are newcomers to the world of radio frequency (RF) electronics, but seasoned vets are welcome to give it a go as well. Please report any suspected errors to me via e-mail.

1. What comprises radio frequency signals?

a)  A stream of photons.
b)  Electromagnetic waves.
c)  Alpha rays (protons).
d)  Beta rays (electrons).

2. How does an antenna achieve gain when it has no active signal amplification?

a)  Excess electrons within the antenna structure increase the signal power.
b)  Gain is achieved by directing (concentrating) a majority of the signal in a preferred direction rather than equally in all direction.
c)  By varying the diameter of the radiating elements.
d)  Antennas do not provide any sort of gain.

3. Why do RF people often speak of power in units of dBm and dBW rather than milliwatts and watts, respectively?

a)  They are equivalent and therefore are interchangable.
b)  Using Latin words makes them appear intelligent.
c)  Scientific calculators and computer algorithms handle dBm and dBW more efficiently.
d)  Using dBm or dBW (decibels relative to a milliwatt or watt, respectively) allows multiplication and division of gains and losses to be performed as addition and subtraction, respectively.

4. Why do coaxial (coax) cables specify a minimum bend radius?

a)  Too tight of a bend alters the internal physical dimension to where the impedance change profoundly affects the internal signal.
b)  To prevent breakage.
c)  The outer insulation might split if the bend is too tight.
d)  Coaxial cables do not have a minimum bend radius.

5. Why do discrete components - resistors, capacitors, and inductors - eventually not work as frequencies increase beyond some point?

a)  Quantum mechanical tunneling dominates at high frequencies.
b)  Brownian motion randomizes the electron "walk,' and thereby limits the frequency.
c)  Parasitic resistance and reactance progressively dominates the component impedance as the frequency increases.
d)  There is no frequency dependence in discrete components.

6. What can cause a poorly shielded AM or FM radio to change its audio level as you vary your distance from it?

a)  Your body creates half of a capacitor (the radio and/or antenna is the other half) that can alter the resonant frequency of the radio's local oscillator(s).
b)  Your fingers act like windings an inductor and detune the circuit.

7. What does the "S" in S-Parameters stand for?

a)  Splattering.
b)  Scintillation.
c)  Stability.
d)  Scattering.

8. What is the phase shift at the shorted end of a coaxial cable?

a)  0°
b)  90°
c)  180°
d)  360°

9. At what rate does the power of an RF signal attenuate in free space?

a)  2 dB for every doubling of distance.
b)  4 dB for every doubling of distance.
c)  6 dB for every doubling of distance.
d)  8 dB for every doubling of distance.

10. What is the name of the frequency band occupied by license-free devices such as WiFi routers and Bluetooth headphones?

a)  ISM (Industrial, Scientific, and Medical)