# Is time switching possible with FDM (Frequency Division Multiplexing)?

Your answers should have detailed explanations. Topics: frequency division multiplexing, time division multiplexing, electromagnetic waves, radio-wave propagation, TDM in telephony, FDMA, TDMA access, spread spectrum, frequency-hopping systems, pseudo-random noise sequence, direct-sequence systems, attenuation, transmitting antenna gain, receiving antenna gain.

Questions:

1) A voice signal, has a maximum of 6KHz. How many of this signal will fit into a 1.8MHZ spectrum allocation (If using SSBSC Amplitude modulation)?2) A voice signal, has a maximum of 4KHz. How many of this signal will fit into a 1.2MHz spectrum allocation (If using DSB Amplitude modulation)?3) Explain the idea behind spread-spectrum technique.

4) Is time switching possible with FDM (Frequency Division Multiplexing)? Explain.5) Explain what a PN (Pseudo-random noise) sequence is.

6) Explain what “Spreading gain” is.7) Why is it preferable for all CDMA signals using a given frequency to have orthogonal PN codes?8) When do we use ground-wave propagation for better results?9) What are the advantages of ionospheric propagation?10) Define index of refraction.11) What are the similarities between radio waves and light waves?12) Explain why total reflection is possible when radiation travels from a medium of higher index of refraction to one with lower refractive index, but not when radiation travels in the other direction.13) What is the speed of radio waves in free space?14) What is the “attenuation of free space” due to?

15) In a radio wave, what is the relationship between its polarization and electric field?

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