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The term downconverter refers to a device that takes an input signal (typically electronic) and outputs a signal at a lower frequency that preserves some signal characteristics (downconversion). Radio telescopes generally include such a device, lowering the frequency of the received signal (from the antenna, often amplified) with the intention of preserving the relevant information within a particular band of interest. The observed frequencies-of-interest may be very high (in the MHz or GHz range, which are within the frequency range of radio, i.e., radio frequency or RF). A sufficiently lower frequency can more easily be carried by cable and/or can be low enough to be digitized and processed using digital techniques, which offer the flexibility to extract additional information of interest.
Such downconverters are also commonly used in radio-based communication and radar. Conventional downconverters are heterodyne circuits, forming a (lower) beat frequency to serve as the output.