Unit 1 Assignment 1 Blank Answer Sheet
Name: Date: Electronics ET2530
1. Define Modulation. The process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that contains information to be transmitted.
2. What is a carrier Frequency? A carrier frequency is a single radio frequency with steady amplitude.
3. Describe two reasons that modulation is used for communications transmissions.
a) Signal integrity
b) Power savings
4. List three parameters of a high frequency carrier that may be varied by a low frequency intelligence signal. Amplitude, frequency and phase v = Vp·sin(ωt + Φ) ω = 2πf (describe which parameters can be varied)

5. What are the frequency ranges included in the following frequency subdivisions: MF (medium frequency)300-3000kHz, HF (high frequency)3-30MHz, VHF (very high frequency)30-300MHz, UHF (ultra-high frequency)300-3000MHz, and SHF (super high frequency)3-30GHz?
7. A microwave transmitter typically requires a +8dBm audio level to drive the input fully. If a +10 dBm level is measured, what is the actual voltage level measured? Assume a 600Ω system. (2.45V)
Hint: Use this equation and solve it for V2 10 dBm = 20 · log10 (V2/0.77459)

9. Convert the following power to their dBm equivalents: (a) p = 1 W = 30.0000dBm (b) p = 0.001 W = 0.00000dBm (c) p = 0.0001W = -10.0000dBm (d) p = 25 μW = dBm Use this formula: dBm = 10 · log10 [P2/(10-3)]

15. Define electrical noise and explain why it is so troublesome to a communications receiver. Noise is a random fluctuation in an electrical signal and is an error or undesired random disturbance of a useful information.

16. Explain the difference between internal and external noise. Internal noise is that which a system generates on its own and external noise comes from an external source.
23. Calculate the S/N ratio for the receiver output of a 4V signal and 0.48 V noise both as a ratio and in decibel form. (69.44, 18.42 dB) For ratio form: S/N = signal power/noise power = Ps/Pn = (Vs2/R)/(Vn2/R) = Vs2/Vn2 =69.44? For decibel form use: = 10·log10(S/N) = 6.94? dB

32. Calculate the noise power at the input of a microwave receiver with an equivalent noise temperature of 45 K. It is fed from an antenna with a 35 K equivalent noise temperature and operates over a 5 MHZ bandwidth. (5.52 x 10-15 W) Teq receiver = 45 K Teq antenna = 35 K Δfeq = 5(106) Use T = Teq receiver + Teq antenna Pn= k·T·Δfeq =

37. Define information theory.
38. What is Hartley’s Law? Explain its significance. The maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise and maximum amount of error-free digital data that can be transmitted with a specified bandwidth in the presence of the noise interference.
40. What is the seventh harmonic of 360 Hz? (2520 Hz) The seventh harmonic f7 = 360,000 Hz × 7 = 2,520,000 Hz = 2520 kHz.
49. Define resonance and describe its use. Resonance is the tendency of a system to oscillate with greater amplitude at some frequencies than at others at these frequencies, even small periodic forces can produce large amplitude oscillations, because the system stores vibration energy.
50. Calculate an inductor’s Q at 100 MHz. It has an inductance of 6 mH and a series resistance of 1.2 kΩ. Determine its dissipation. (3.14 x 10, 0.318 x 10-3) Q = reactance / resistance = ω·L / R ω = 2·π·f Q = 2·π·f·L /R = D = 1 /Q =

55. Define the quality factor (Q) of an LC bandpass filter. Explain how it relates to the “selectivity” of the filter. Describe the major limiting value on the Q of a filter.

65. Draw schematics for Hartley and Colpitts oscillators. Briefly explain their operation and differences.
Hartley Oscillator
Positive feedback to the input is provided by the tapped coil.
Foscillation≈ 1/[2·π·(L1+L2)·C]
Colpitts Oscillator
Positive feedback to the input is provided by capacitors
Foscillation≈ 1/[2·π·(C1·C2)/(C1+C2)·L]