Radio Systems Engineering by Héctor J. De Los Santos Christian Sturm & Juan Pontes

Author:Héctor J. De Los Santos, Christian Sturm & Juan Pontes
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Fig. 6.1Homodyne (zero-IF) receiver architecture

Fig. 6.2Heterodyne receiver

In the homodyne receiver (also referred to as, direct conversion, or zero-IF, i.e., with no intermediate frequency) the desired incoming RF frequency is translated directly to baseband , where it is process and the modulation information recovered. As indicated in an earlier chapter, the baseband signal contains the range of frequencies occupied by the signal before modulation or after demodulation. These signals normally occupy frequencies well below the carrier frequencies, even approaching DC on the low end.

In the heterodyne receiver the desired incoming RF frequency is translated to one or more intermediate frequencies before demodulation. The modulation information, in turn, is recovered from the last IF frequency.

In a dual-conversion superheterodyne receiver, Fig. 6.2, successive mixers translate the RF signal to two IF frequencies. LO signals, tuned at a particular spacing above or below the RF signal, drive the mixer circuits. The RF and LO signals mix to produce a difference frequency known as the IF frequency. The result is a dual-conversion receiver, described as such because of the two down-conversion mixers.

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