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In electronics, a local oscillator (LO) is an electronic oscillator used with a mixer to change the frequency of a signal. This frequency conversion process, also called heterodyning, produces the sum and difference frequencies from the frequency of the local oscillator and frequency of the input signal. Processing a signal at a fixed frequency ...
A direct-conversion receiver (DCR), also known as a homodyne, synchrodyne, zero intermediate frequency or zero-IF receiver, is a radio receiver design that demodulates the incoming radio signal using synchronous detection driven by a local oscillator whose frequency is identical to, or very close to the carrier frequency of the intended signal.
The IC has a front end, mixer, IF and demodulation and provides received audio. In order to suppress local oscillator leakage and provide a slight amount of image rejection, a varactor and a coil provide one stage of tracking bandpass filtering. Typical for single-chip receivers, the dynamic range of this receiver is poor.
IQ imbalance is a performance-limiting issue in the design of a class of radio receivers known as direct conversion receivers. [a] These translate the received radio frequency (RF, or pass-band) signal directly from the carrier frequency to baseband using a single mixing stage.
A new detection system was required and this would rely on detecting leakage signals from the local oscillator used in superheterodyne radio receiver circuits. Transmissions at this time were on the 405-line system and used the Band I (47 to 68 MHz), Band II (87.5 to 108.0, VHF / FM sound-only radio [ ii ] ) and Band III (174 to 240 MHz) VHF bands.
In optical interferometry, homodyne signifies that the reference radiation (i.e. the local oscillator) is derived from the same source as the signal before the modulating process. For example, in a laser scattering measurement, the laser beam is split into two parts. One is the local oscillator and the other is sent to the system to be probed.
Carrier frequency offset often occurs when the local oscillator signal for down-conversion in the receiver does not synchronize with the carrier signal contained in the received signal. This phenomenon can be attributed to two important factors: frequency mismatch in the transmitter and the receiver oscillators; and the Doppler effect as the ...
The Dick effect (hereinafter; "the effect") is an important limitation to frequency stability for modern atomic clocks such as atomic fountains and optical lattice clocks.It is an aliasing effect: High frequency noise in a required local oscillator (LO) is aliased (heterodyned) to near zero frequency by a periodic interrogation process that locks the frequency of the LO to that of the atoms.