simulation of a superheterodyne receiver using pspice - School of ...

More documents

Recommendations

Info

Fig. 46: AM signal in superhetrodyne receiver. Taking a look at the Fourier transform in Fig. 47 displays the two signals going into the mixer and the sum and difference frequencies in the mixer output. Fig. 47: Mixer spectrum. Although the mixer load is tuned to 455kHz the spectrum above shows spectral peaks decreasing in amplitude at 910kHz, 1MHz, 1.455MHz, 1.91MHz, 2MHz, 2.455MHz etc. There is also an unwanted spectral peak at 555kHz. The only possible reason for this is that the image frequency is causing distortion in the 42
spectrum. However, as long as the IF stages are correctly tuned and have sufficient gain the difference frequency will be selected and amplified while the other frequencies attenuated. This is viewed in the IF spectra below in Fig. 48. Fig. 48: IF spectra. The difference frequency (i.e. the desired frequency) has an amplitude of 40mV at the output of the mixer. This is now applied to the two IF amplifiers. The output of the first IF stage shown in the second plot of Fig. 48, it is noted that the difference frequency lies at 600mV at this stage. This implies that IF1 has a gain of 15. The third plot of Fig. 48 displays the output of the second IF stage. At this point the difference frequency is now at 12.6V. The second IF stage has a larger gain than the first stage (i.e. 12.6V/600mV = 21). A very important feature that can be seen from Fig. 48 is that all other frequencies apart from the selected one are greatly attenuated by the IF amplifiers. The AM detector has the function of detecting this highly amplified IF signal. As can be seen from the sixth plot of Fig. 46 previously the AM detector begins to trace or “detect” the IF signal. The detector has diode rectification at its input and the first plot on Fig. 49 below shows the rectification of the signal at 455kHz with 43
Page 1 and 2: SIMULATION OF A SUPERHETERODYNE REC
Page 3 and 4: CHAPTER 1: PROJECT ORGANISATION. Th
Page 5 and 6: modulating signal (Sensitivity). A
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: The first major test for the superh
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

simulation of a superheterodyne receiver using pspice - School of ...

Create successful ePaper yourself

Delete template?

Save as template?