- Heterodyne detection
Heterodyne detection is a method of detecting radiation by non-linear mixing with radiation of a reference frequency. It is commonly used in
telecommunications andastronomy for detecting and analysing signals.The radiation in question is most commonly either radio waves (see
superheterodyne receiver ) or light (seeOptical heterodyne detection orinterferometry ). The reference radiation is known as thelocal oscillator . The signal and the local oscillator are superimposed at a mixer. The mixer, which is commonly a (photo-)diode , has a non-linear response to the amplitude, that is, at least part of the output is proportional to the square of the input.Let the electric field of the received signal be
:
and that of the local oscillator be
:
For simplicity, assume that the output of the detector "I" is proportional to the square of the amplitude::
:
::
:::
::
The output has high frequency ( and ) and constant components. In heterodyne detection, the high frequency components and usually the constant components are filtered out, leaving the intermediate (beat) frequency at . The amplitude of this last component is proportional to the amplitude of the signal radiation. With appropriate
signal analysis the phase of the signal can be recovered as well.ee also
*
Heterodyne
*Homodyne detection
*Optical heterodyne detection
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