A Tuner Circuit Analysis - Report Example

Introduction A tuner circuit is one that allows an output only at a certain input frequency. The circuit is widely used incommunication and its function is channel selection. It normally receives radio frequencies and then converts the selected carrier frequency and the bandwidth associated with it into a fixed frequency that is best suitable for further processing mainly due to the fact that a lower frequency is used on the output (Bertrand, 2002). The least complicated tuner is comprised of an inductor and capacitors which are normally connected either in parallel or series and either the capacitor of the inductor is made variable. This then creates a resonant circuit which is able to respond to the alternating current that has a single frequency. Tuner circuits are used in radios, televisions and all the other devices that require tuning during their operations (Carr, 2004). At any time when the characteristics of the inductance and the capacitance of the circuit are found in the tuned circuit, the process of resonance takes place. In a circuit with alternating current, the inductor normally produces inductive resistance which then results in a lag in the current to a voltage of about 90 degrees. Since the inductor normally reacts to the changing current, it is normally referred to as the reactive component of the circuit (Bertrand, 2002). The opposition that is produced by the inductor to the alternating current is referred to as the reactance. This opposing effect is caused by the reaction of the inductor to the changing current of the alternating current source (Builder, 2002). Both the inductance and the frequency of the circuit determine the magnitude of the reactance that is realized in the circuit. The capacitor usually produces a reactance which then results in the current leading by about 90 degrees (Hassan, 2002). The capacitor usually reacts by changing the voltage of the system and it is thus referred to as the reactive component of the circuit. The opposition on the capacitor is referred to as the capacitive reactance of the circuit. When an inductor produces inductive reactance in an alternating current circuit and the result is lagging, an increase in the frequency will result into an increase in the inductive resistance of the circuit (Hassan, 2002). Therefore, the inductive resistance of the circuit usually varies directly to the frequency of the circuit. The opposition results from the functioning of the capacitor and produces the reactance force. The capacitive reactance of the circuit is inversely proportional to the frequency of the system and decreases with an increase in the frequency of the system (Carr, 2004). A low frequency thus results into a greater capacitive reactance while a high frequency will give a low reactance in a particular capacitor on the circuit (Bertrand, 2002). In this experiment, we are tasked to build a circuit and establish at what frequency of the input signal an output is produced. Figure 1: The set-up of the tuner circuit Objectives a. To determine the operation of the tuner circuit. b. To determine the input frequencies needed for the generation of waveforms. Methods a. The circuit of the tuner system is built as shown in figure 1 above. b. The circuit is then connected to the input of a function generator and the signal input is set to approximately 100 Mv peak-to-peak and 5KHZ. One is allowed to use one channel of the oscilloscope to set the voltage. The voltage of the oscilloscope doesn’t have to be accurate. c. The next step involves the connection of the other channel of the oscilloscope to the output of the system. Little or no output should be seen on the screen of the simulator. d. The next step involves increasing the frequency of the input signal and keeps watching the output signal. At some input frequency an output will be generated. e. Make a note of this frequency and sketch the waveform that is generated. Results At a frequency of 142.0 kHz, the output was generated and the amplitude waveforms of the resulting output are as shown below. Figure 2: The generated waveform at 142.0 kHz Figure 3: The generated waveform at 5.0 kHz Discussion From the waveforms at frequencies of 142.0 KHz and 5.0 KHz, the input waveforms are similar in both shape and appearance but as the frequency decreases, the output waveforms appear to undergo distortion. This is an indication of the increasing capacitive reactance. A decrease in the frequency of the system results into creation of a more complex pattern of the waveform. At 5.0 kHz, the complex pattern can be observed as it appears jagged on the lower phase of the wave. The sine waves of the system can be noted as being aligned to the zero phase angle of the waveform. This implies that the starting point of all the waves is the same at 0o and the cycle of the system increases from a zero magnitude of the amplitude. The highest value of the amplitude on the waveform is experienced at a frequency of 142.0 KHz. The complexity of the system can be increased substantially by decreasing the frequency of the system. Waves at lower frequency are observed to start at 0o and move on with a triangular wave on the lower side of the lower amplitude while the upper amplitude remains with a fixed ratio across the waveform. As the waveform increases infinitely, this results into a triangular waveform as shown in figure 3 above. This complex pattern of the waveform can be explained from the behavioral operations of the tuner circuit. The tuner circuit has the capacity to store energy and it is capable of taking energy that is fed to it from a source of power and store it in an alternate manner in both the inductor and the capacitor (Bertrand, 2002). The output of the system can then be produced as an alternating current waveform. When the voltage is applied across the capacitor, it is able to acquire charge to a potential equivalent to that of the source of power. When the circuit is completed, it circuit creates a path for the flow of electrons on the upper plates of the capacitors to the lower plates and therefore starts to neutralize the already available charges (Hassan, 2002). As the electrons continue flowing through the coil, a magnetic wave is then built up and this energy is then transferred to the electromagnetic field of the inductor. When the capacitor is fully discharged, a maximum magnetic field is created and the energy that is stored in the capacitor is transferred to the magnetic field. With the capacitor being fully discharged, the magnetic field starts to collapse and this causes the flow of current in the same direction hence charging the capacitor again but with a different polarity (Carr, 2004). The inductor is therefore able to produce low impedance to low frequency signals and an increase of the impedance results into a decrease in the frequency. The energy is then fully stored again in the capacitor. When there is one frequency at which the parallel combination of an inductor and capacitor offer maximum impedance and thus the system is tuned to this frequency (Builder, 2002). The oscillator is able to tolerate an action of clipping on its signal unlike the series circuit which results into a degeneration of the signal (Bertrand, 2002). If more time is allowed for the clipping, this comes out as a major advantage and uniform amplitude can be produced. A 10 volts bias signal is created in the circuit and the resistors create a voltage ladder that then results into a voltage bias at a point close to the forward voltage drop of the circuit (Carr, 2004). This allows the process of rectification to take place and thus monitor the output signal on the circuit. A repetition of the process will help to determine the average results. Conclusion From the discussion we can conclude that the tuner circuit operates in the same manner as a water tank where the energy is stored in the liquid. In this analogy, the resonance in the circuit will only occur when the value of both the capacitive and inductive reactance are equal to each other. The total amount of impedance that is in the circuit will approach infinity as the amount of power frequency that is supplied to the circuit approaches the resonance. The trend of the resonance is dependent on the type of connection on the circuit and thus for a parallel circuit, the resonance approaches infinity while a series connection, the resonance will be equal to zero. The relationship between the capacitive reactance, the frequency and the inductive reactance is also very important in the operation of the tuning circuits. As discussed above, an increase in the sections above, an increase in the frequency will result into an increase in the inductive resistance of the circuit and an increase in the capacitive reactance of the circuit decreases the frequency of the system. This way, the process of auto tuning becomes possible in various devices. The main objectives of the experiment have been achieved and the process of operation of the circuit has been determined. The frequencies at which output signals are produced has also been determined and sketched. References [1] Ron Bertrand, Online Radio and electronics course (2002). Retrieved from: http://arcarc.xmission.com/PDF_Electronics/RLC%20circuits%20&%20Resonance.pdf Viewed on 30th march 2015. [2] Hassan K Khalil, Nonlinear Systems, Prentice Hall, (2002) Retrieved from: http://www.eolss.net/sample-chapters/c18/E6-43-21.pdf Viewed on 30th march 2015. [3] Tuned circuits. Retrieved from: http://www.navymars.org/national/training/nmo_courses/nmo1/module9/14181_ch1.pdf Viewed on 30th march 2015. [4] Joseph J. Carr, Secrets of RF Circuit Design, McGraw-Hill, 3rd edition, (2004). Retrieved from: http://www.ik4hdq.net/doc/testi/segr_circ_RF.pdf Viewed on 30th march 2015. [5] Tuned circuits. Retrieved from: http://electronics-lab.info/Files/I3/8.%20Tuned%20circuits.pdf Viewed on 30th march 2015. [6] G. Builder, Tuned Circuits (2002). Retrieved from: http://www.ax84.com/static/rdh4/chapte09.pdf Viewed on 30th march 2015. Read More