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# Itt Unit 1 Elec Comm

In: Science

Words 483
Pages 2
1. Define modulation.
Impressing a low-frequency intelligence signal onto a higher-frequency carrier signal
2. What is carrier frequency?
The higher frequency that carries the modulation(Intelligience)
3. Describe the two reasons that modulation is used for communications transmissions.
To transfer information, such as voices, images, or data. Also, the frequencies employed by the modulated signal are high enough to permit the use of antennas of reasonable length. 4. List the three parameters of a high-frequency carrier that may be varied by a low-frequency intelligence signal. amplitude, frequency, and phase
5. What are the frequency ranges included in the following frequency subdivisions: MF (medium frequency), HF (high frequency), VHF (very high frequency), UHF (ultra high frequency), and SHF (super high frequency)?
MF:300 kHz–3 MHz, 3-30MHz: HF, 30–300 MHz: VHF, 300 MHz–3 GHz: UHF, 3–30 GHz: SHF
7. A microwave transmitter typically requires a +8-dBm audio level to drive the input fully. If a +10-dBm level is measured, what is the actual voltage level measured? Assume a 600- sys- tem. (2.45 V)
9. Convert the following powers to their dBm equivalents:
(a) p = (b) p = (c) p = (d) p =
1 W (30 dBm) 0.001 W (0 dBm) 0.0001 W (-10 dBm) 25mW (-16 dBm)
15. Define information theory.
16. What is Hartley’s law? Explain its significance.
23. A triangle wave of the type shown in Table 1-3(e) has a peak-to-peak amplitude of 2 V and f = 1 kHz. Write the expression v(t), including the first five harmonics. Graphically add the harmonics to show the effects of passing the wave through a low-pass filter with cutoff fre- quency equal to 6 kHz.
27. Explain the difference between external and internal noise. Internal noise is that which a system generates on its own and external noise comes from an external source.
32. Determine the noise current for the resistor in Problem 29. What happens to this noise current
37. A three-stage amplifier has an input stage with noise ratio (NR) = 5 and power gain (PG) = 50. Stages2and3haveNR = 10andPG = 1000. Calculate the NF for the overall system. (7.143dB)
38. A two-stage amplifier has a 3-dB bandwidth of 150 kHz determined by an LC circuit at its input and operates at 27°C. The first stage has PG = 8 dB and NF = 2.4 dB. The second stage has PG = 40 dB and NF = 6.5 dB. The output is driving a load of 300 . In testing this system, the noise of a 100-k resistor is applied to its input. Calculate the input and output noise voltage and power and the system noise figure. (19.8mV, 0.206 mV, 9.75 * 10-16 W, 1.4 * 10-10 W, 3.6 dB)
40. List and briefly describe the four basic troubleshooting techniques.