EKT 358 Sistem Perhubungan [Communication Systems]

Transcription

1 EKT 358 Sistem Perhubungan [Communication Systems] Assignment 2 Question 1 [C5, CO2, PO1, PO2] A radio broadcasting station using AM with its carrier frequency of 500 khz with a peak amplitude of 32 V. This carrier is modulated by a single-tone modulating frequency of 12.0 khz whose amplitude is sufficient to produce a +14 Vp change in the amplitude of the envelope. Calculate the following: i. frequency limits for the upper and lower sidebands.. [2 Marks / Markah] ii. peak amplitude of the upper and lower side frequencies. [2 Marks / Markah] iii. the modulation index, m. [1 Marks / Markah] iv. the percentage modulation. [1 Mark / Markah] v. maximum and minimum positive amplitude of the AM envelope. [2 Marks/ Markah] vi. Illustrate and label the envelope of this AM modulated wave. [3 Mark / Markah] (iv) Explain what will happen if the peak amplitude of the audio signal is higher than the peak amplitude of the carrier signal. [ Terangkan apa akan terjadi sekiranya amplitud puncak bagi isyarat audio lebih tinggi daripada amplitud puncak bagi isyarat pembawa.]

2 ! [2 Marks/Markah] Question 2 [C5, CO2, PO1 and PO2] (a) Given the total power of an amplitude modulated (AM) wave is 2500W. Evaluate the power content of the carrier and the each of the sideband power if the AM signal is 60% modulated. [Diberi jumlah kuasa keseluruhan bagi satu gelombang pemodulatan amplitude sebagai 2500W.sekiranya isyarat AM itu dimodulatkan sebanyak 60%]. [3 Marks/Markah] [C6 CO2, C5, PO1,PO2] (b) In the real world, it is difficult to determine AM power by measuring the output voltage and calculating the power with expression! P = V 2. However, it is easy to measure the R current in the load using Radio Frequency (RF) ammeter. When the antenna impedance is known, the output power is easily calculated. [Di alam nyata adalah sukar untuk mengira kuasa AM dengan hanya mengukur keluaran voltannya dan pengiraan kuasa dengan ungkapan P! = V 2. Walaubagaimana pun, pengukuran arus di beban boleh R dilakukan dengan ammeter RF. Apabila galangan antena di ketahui, kuasa keluaran senang dikira.] (i) Prove that the total current at the transmitting end can be calculated as : [Buktikan indek modulasi boleh dikirakan sebagai :] I T = I c ( 1 + m2 2 ) Where, [di mana,] IT = Total current in the antenna. [Jumlah arus dalam antena] IC = Current produced by the carrier [Arus yang dihasilkan oleh pembawa] M= modulation index

3 ! [Indeks pemodulatan] [3 Marks / Markah] Calculate the modulation index, m and total load power, PT if the given antenna has an impedance of 75 Ω and experiences an antenna current change from 8A unmodulated to 8.4A. [Kirakan indeks pemodulatan, m dan jumlah kuasa beban, PT sekiranya antena yang diberikan mempunyai 75 Ω dan mengalami perubahan arus antena dari 8A tak termodulat kepada 8.4A] Question 3 [C6, CO2, PO1, PO2] (a) Figure 2 shows the Single Side Band (SSB) generation using the phasing method, respectively. Develope the SSB output using mathematical representation. [Rajah 5(a) menunjukkan penjanaan SSB menggunakan kaedah pemfasaan. Binakan keluaran SSB menggunakan perwakilan matematik.] Figure 2 [Rajah 2] [5 Marks/Markah]

4 [C5, CO2, PO1, PO2] (b) AM Single Side Band (AM SSB) was introduced to overcome disadvantages of AM double side band (AM DSB). Justify how this AM SSB is better than AM DSB. [AM SSB diperkenalkan untuk mengatas ikelemahan AM DSB. Berikan justifikasi bagaimana A M SSB adalah lebih baik berbanding AM DSB] [ [5 Marks/Markah] (c ) An antenna transmits a 10kW power at 95% modulation using conventional AM. Calculate the amount of power saving if AM Single Side Band (SSB) transmission is used for the same intelligibility. [5 Marks/Markah] (d)a SSB- SC transmission contains 10kW. This transmission is to be replaced by a standard amplitude-modulated signal with the same power content. Determine the power content of the carrier and each of the sidebands when the percent modulation is 75%. [Satu pemancaran SSB-SC mempunyai 10kW. Pemancaran ini akan digantikan dengan signal pemodulatan amplitud standard dengan nilai kuasa yang sama. Tentukan nilai kuasa dalam pembawa dan setiap jalur sisi apabila peratusan pemodulatan adalah 75% ] [4 Marks/Markah] Question 4 (C4, CO2, PO1 and PO2) (a) An AM transmitter puts a 500 khz carrier of 6A into an antenna whose resistance is 52 Ω. The transmitter is modulated by 60 percent (60%). Evaluate: [Sebuah pemancar AM meletakkan pembawa 500kHz berarus 6A kepada antenna yang mempunyai rintangan 52 Ω. Pemancar tersebut dimodulatkan sebanyak 60%.Nilaikan] (i) The output power. [Kuasa keluaran.] The total sidebands power. [Jumlah kuasa jalur sisi] (4 Marks/Markah) (1 Mark/Markah) (C4, CO2, PO1 and PO2)

5 (b) An AM signal in which the carrier is modulated 70% contains 1500W at the carrier frequency. Determine the power content of the upper and lower sidebands for this percent modulation. Calculate the power at the carrier and the power content of each of the sidebands when the percent modulation drops to 50%. Discuss the effect of the modulation drop on the carrier power and the total transmitted power. [Satu signal AM di mana pembawa telah dimodulatkan sebanyak 70% mempunyai 1500W pada frekuensi pembawa. Nilaikan kandungan kuasa bagi jalur sisi atasan dan bawahan untuk peratusan pemodulatan ini. Kirakan kuasa pembawa dan kandungan kuasa setiap jalur sisi bila peratusan pemodulatan menyusut kepada 50%.Bincangkan kesan penyusutan permodulatan ke atas kuasa pembawa dan jumlah keseluruhan kuasa yang dihantar] (5 Marks/Markah) Question 5 (C2, CO2, PO1 and PO2) (a) Amplitude Modulation (AM) double-sideband full carrier (DSBFC) is the most commonly used and the oldest and simplest form of AM modulation. Sometimes is also called conventional AM or simply AM. [Jalur sisi berganda berpembawa penuh AM ( DSBFC) adalah bentuk modulasi AM yang sering digunakan dan merupakan bentuk yang paling lama dan paling mudah. Kadangkala dikenali sebagai AM konvensional atau hanya AM.] (i) Discuss the relationship between the modulating signal frequency and the bandwidth in a conventional AM. [Bincangkan hubungan di antara frekuensi signal pemodulat dan jalur lebar di dalam AM konvensional.] For 100% modulation, define the relationship between the voltage amplitudes of the side frequencies and the carrier. [Untuk permodulatan 100%, tafsirkan hubungan di antara amplitud frekuensi sisi dan amplitud pembawa.] (C4, CO2, PO1 and PO2) (b) One input to a conventional AM modulator is a 40 Vp amplitude signal at 500 khz frequency, while the other input is a 20 khz signal with sufficient amplitude to cause a change in the output wave of +/- 10Vp. The load resistance is given as 10Ω. Calculate: [Satu masukan kepada pemodulasi AM konvensional adalah signal beramplitud 40 Vp puncak pada frekuensi 500 khz, manakala satu lagi masukan adalah signal 20 khz dengan amplitud yang memadai untuk menyebabkan perubahan kepada gelombang keluaran sebanyak +/- 10V puncak. Beban galangan diberi sebanyak 10 Ω. Kirakan:] (i) Maximum and minimum amplitude of the modulated wave. [Amplitud maksimum dan minimum gelombang termodulat] Modulation coefficient and percentage of modulation

6 [Indeks pemodulatan dan peratusan pemodulatan] (iii) (1 Mark/Markah) Peak amplitude of the modulated carrier and peak amplitudes of the sidebands. [Amplitud puncak isyarat pembawa, dan amplitud puncak jalur sisi] (iv) The total power of the modulated wave. [Jumlah keseluruhan kuasa gelombang termodulat] (3 Marks/Markah) (v) =82.5W Re-calculate the total power if only single sideband full carrier (SSBFC) modulated signal is received. Illustrate the power spectrum received and comment on the power saving for SSBFC. [Kira semula kuasa keseluruhan sekiranya hanya satu isyarat jalursisi (SSBFC) termodulat diterima.gambarkan spectrum kuasa diterima dan beri komen ke atas penjimatan kuasa bagi satu jalursisi pembawa penuh (SSBFC).]