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Super heterodyne receiver

Super heterodyne receiver. Prepared by : Abdullah Ba-Sulaiman & Yasser Badahdah, EE370, Sec# 1, Edited by : Dr. Ali Muqaibel. What is the intermediate frequency f if ? It is fixed frequency located at 455 kHz

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Super heterodyne receiver

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  1. Super heterodyne receiver Prepared by : Abdullah Ba-Sulaiman & Yasser Badahdah, EE370, Sec# 1, Edited by : Dr. Ali Muqaibel

  2. What is the intermediate frequency fif? • It is fixed frequency located at 455 kHz • The IF filter is band-pass with center frequency of 455 kHz and bandwidth equal to the bandwidth of one AM channel approximately =10 kHz. -Fc -Fif Fif Fc

  3. Why do we need the IF Stage? • It is too difficult to design a tunable and sharp filter. So we design sharp & fixed filter. • The channel to be filtered out should first be frequency shifted to the IF frequency by a frequency converter as shown in the super heterodyne Figure -Fc -Fif Fif Fc

  4. Up conversion Fc+Fif -Fc -Fif Fif Fc -2Fc-Fif -Fif Fif 2Fc+Fif Second Image Subtract Fc+Fif First Image Add Fc+Fif

  5. Down conversion Fc-Fif -Fc -Fif Fif Fc -2Fc+Fif -Fif Fif 2Fc-Fif Second Image Subtract Fc-Fif First Image Add Fc-Fif

  6. Why up conversion is better than down conversion? The range of radio station on AM is: 550kHz→1600kHz Up (Fc+Fif): 1005kHz→2055kHz ratio frequency is 1:2 down (Fc-Fif): 95kHz→1155kHz ratio frequency is 1:12 We see the ratio frequency in up conversion is smaller than in down conversion which means it is easier to design.

  7. Why we filter at RF stage? Image station -Fc-2 Fif -Fc -Fif Fif Fc Fc+2 Fif After up conversion Now the signal is not clear -Fif Fif The image station is a station that is spaced by 2*Fif from the desired station as shown in the figure

  8. The image station will be canceled RF filter -Fc-2 Fif -Fc -Fif Fif Fc Fc+2 Fif After up conversion Now the signal is clear -Fif Fif

  9. For example: we takeFc=882kHz(the Holy Quran station ) -1792kHz -882kHz -455kHz 455kHZ 882kHz 1792kHz After up conversion Now the signal is clear -455kHz 455kHz

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