Concept Flashcards

Concept Flashcards#

1. What are the four main types of communication media?

  • Transmission lines

  • Waveguides

  • Optical fibers

  • Wireless

2. What is the relationship between wavelength and frequency?
\[ \lambda = \frac{c}{f} \]
3. What happens to wavelength as frequency decreases?

Wavelength increases as frequency decreases.

4. What are the advantages of transmission lines?

  • Reliable

  • Easy to repair

  • Secure

5. How do transmission lines behave at high frequencies?

They act like a low-pass filter.

6. What type of filter does a waveguide behave like?

High-pass filter

7. What is the waveguide cutoff frequency equation?
\[ f_{c/o} = \frac{c}{2a} \]
8. Why do waveguides block low frequencies?

Low frequencies have long wavelengths that cannot propagate in the structure.

9. What are the advantages of optical fibers?

  • Very high bandwidth

  • Low loss

  • Multiple signals (WDM)

10. What is the main disadvantage of optical fibers?

Difficult to install and repair

11. What are the advantages of wireless communication?

  • Flexible

  • Low infrastructure cost

12. What are the disadvantages of wireless communication?

  • Limited bandwidth

  • Less reliable

13. What are the four RF propagation methods?

  • Line-of-sight (LOS)

  • Surface wave

  • Sky wave

  • Forward scatter

14. What limits line-of-sight communication?

Earth curvature and antenna height

15. What propagation method allows signals to follow the Earth's surface?

Surface wave propagation

16. How does frequency affect surface wave propagation?

Higher frequency → more attenuation → shorter range

17. What is sky wave propagation?

Reflection/refraction of RF signals from the ionosphere back to Earth

18. What is skip distance?

Distance between transmitter and first point where sky wave returns

19. What is a quiet zone?

Region where neither surface wave nor sky wave is received

20. What is forward scatter propagation?

Signal scattering off atmospheric irregularities beyond the horizon

21. What is the LOS range equation?
\[ r = \sqrt{2h} \]
22. What units are used in the LOS equation?

  • \(h\) in feet

  • \(r\) in miles

23. What are the four steps of a communication system?

  1. Prepare message

  2. Transmit

  3. Receive

  4. Recover message

24. What causes electromagnetic waves in an antenna?

Changing electric and magnetic fields from moving charges

25. What is the length of a half-wave dipole?
\[ L = \frac{\lambda}{2} \]
26. What is the length of a quarter-wave monopole?
\[ L = \frac{\lambda}{4} \]
27. Why does a monopole require a ground plane?

To reflect the field and act like a full dipole

28. What is antenna gain?

Ability of an antenna to focus energy in a direction

29. What is the gain of a parabolic dish antenna?
\[ G = \frac{(2\pi r)^2}{\lambda^2} \eta \]
30. What is the key advantage of phased array antennas?

Electronic beam steering without mechanical movement