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Frequency Range, Local Oscillator Frequency, Image Frequency, and Attenuation

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A radio receiver for the AM broadcast band covers the frequency range 550 to 1600 kHz. The IF frequency is 455 kHz and the local oscillator is above the received signal frequency.

a. What is the frequency range for the local oscillator of the AM radio?

b. The AM radio is tuned to a weak signal at 1260 kHz. What is the local oscillator frequency? What is the image frequency?

c. There is a strong signal at the image frequency you found in part (b) above. The image signal is 40 dB stronger than the wanted signal. The image signal must be 40 dB below the wanted signal in the audio section of the receiver so that it is not heard along with the wanted signal. What attenuation (in dB) must the RF image rejection filter in the AM radio achieve at the image frequency?

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Solution Summary

Local oscillator frequency, image frequency, and attenuation are examined.

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Please see the attachment.
A radio receiver for the AM broadcast band covers the frequency range 550 to 1600 kHz.

The IF frequency is 455 kHz and the local oscillator is above the received signal frequency.

a. What is the frequency range for the local oscillator of the AM radio?

Since the local oscillator is above the received AM Broadcast we can say that the fixed IF frequency is produced as the difference between the variable local oscillator frequency, which we call and the frequency of the wanted AM Broadcast which we call . Thus we can write ...

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