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Aims, objectives and specifications: The aim of this project is to simulate a complete superhetrodyne receiver using Pspice. The specifications set out at the beginning of the project were to take the basic block diagram for the superhetrodyne receiver, shown below in Fig.1, design and simulate each section separately using the MicroSim Pspice program Version8. With this completed use the Pspice Top-down approach with hierarchical design methods to simulate the entire superhetrodyne receiver. Fig. 1:The block diagram of the Superheterodyne receiver. Ref [8] Appendix B Materials and information provided by the supervisor at the start of the project included Ref. [1] “Communication Engineering Theory Notes” and Ref. [2] “Pspice Lab Manual” by Paul Tobin for third year degree in Applied Electronics (SEE3). Reference texts advised: Ref. [3] “Electronic Communication Techniques, Fourth Edition” by Paul Young (Publ. Prentice Hall), Ref. [4] “Pspice for Windows, A Circuit Simulation Primer” by Roy W. Goody (Publ. Prentice Hall), Ref. [5] “Pspice for Windows, Volume 2, Operational Amplifiers & Digital Circuits” by Roy W. Goody (Publ. Prentice Hall). See Appendix B Background theory: The basic requirement for any communications receiver is to have the ability to select a signal of desired frequency, while rejecting closely adjacent frequencies (Selectivity) and provide sufficient amplification to recover the 4
modulating signal (Sensitivity). A receiver with good selectivity will isolate the desired signal in the RF spectrum and eliminate all other signals. This can be achieved using tuned LC circuits resonating at the desired frequency. LC circuits with a high Q value have narrower bandwidths and hence have better selectivity. However it must be noted the bandwidth must be sufficiently large such that it passes the carrier as well as the sidebands to avoid attenuation and hence distortion of the transmitted information. The sensitivity of a communications receiver is a function of the overall receiver gain. In general, higher gain means better the sensitivity. This can be achieved by multiple stages of amplification. There are two types of communications receiver; the Tuned Radio Frequency (TRF) receiver and the Superheterodyne receiver. Although the TRF system is a straightforward concept at high frequencies it becomes difficult to build, is less efficient, has small gain and suffers bandwidth changes. For these reasons among others the Superheterodyne receiver has become the model for all receivers; AM, FM, television, satellite, radar etc. It was developed during WW1 by Edwin Armstrong but did not become popular until the 1930s. Following the block diagram Fig. 1 above, the incoming signal is picked up on the antenna and fed to an RF amplifier. The RF amplifier provides some initial gain and selectivity and minimises radiation of the Local Oscillator (LO) signal through the receiving antenna by isolating the Mixer from the antenna. However, the most important function of the RF amplifier is to eliminate what is known as the image signal. The frequency of this signal is greater than the LO and will mix to give a mixer output at the IF frequency. This will cause problems as after down conversion to IF it will appear at the same frequency as the desired signal and cause interference. Therefore, signals at the image frequency must be eliminated before the mixer stage. The value of the image frequency is: f = f + 2 f image RF IF 5
Page 1 and 2: SIMULATION OF A SUPERHETERODYNE REC
Page 3: CHAPTER 1: PROJECT ORGANISATION. Th
Page 7 and 8: amplitude of the carrier wave varie
Page 9 and 10: Fig. 3: Amplitude Modulator. Settin
Page 11 and 12: This is a quite high value, which m
Page 13 and 14: R Total IN IN 5 = R1 R2 R = 80k 50k
Page 15 and 16: was assumed that the drain-source r
Page 17 and 18: A V = g m R L = 5.56X10 −3 X1X10
Page 19 and 20: 1 Substituting for ω 2 = . LC T β
Page 21 and 22: −3 3 VD = VDD − I DRD = 20V −
Page 23 and 24: Ref. [6] Appendix B Fig. 21: Mixer
Page 25 and 26: Values for the second LC tuned circ
Page 27 and 28: Fig. 24: Double tuned IF amplifier.
Page 29 and 30: Fig. 28: Enlarged section of diode
Page 31 and 32: Fig. 30: AGC and audio signals. The
Page 33 and 34: I C 22.02mA BJT Q12 (pnp transistor
Page 35 and 36: The middle section of the hierarchy
Page 37 and 38: Fig. 40: Block 4 - Local oscillator
Page 39 and 40: Fig. 44: Block 8 - Audio amplifier.
Page 41 and 42: The first major test for the superh
Page 43 and 44: spectrum. However, as long as the I
Page 45 and 46: Fig. 50: Modulating frequency in AM
Page 47 and 48: * Working on the IF stages of the d
Page 49 and 50: are very important) combated this p
Page 51: Fig. 18: Local Oscillator (Amplifie

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