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Local oscillators are used in the superheterodyne receiver, the most common type of radio receiver circuit. They are also used in many other communications circuits such as modems, cable television set top boxes, frequency division multiplexing systems used in telephone trunklines, microwave relay systems, telemetry systems, atomic clocks, radio telescopes, and military electronic ...
The IF signal contains the original modulation (transmitted information) that the received radio signal had at f RF. The frequency of the local oscillator f LO is set so the desired reception radio frequency f RF mixes to f IF. There are two choices for the local oscillator frequency because of the correspondence between positive and negative ...
The RF amplifier may not be needed and is often omitted (or switched off) for frequencies below 30 MHz, where the signal-to-noise ratio is defined by atmospheric and human-made noise. A local oscillator (LO) which generates a radio frequency signal at an offset from the incoming signal, which is mixed with the incoming signal.
The incoming RF signal is first mixed with one local oscillator signal in the first mixer to convert it to a high IF frequency, to allow efficient filtering out of the image frequency, then this first IF is mixed with a second local oscillator signal in a second mixer to convert it to a low IF frequency for good bandpass filtering.
LO is the local oscillator - the carrier sine wave being modulated I(t) and Q(t) are the time-series data for the in-phase and quadrature components. S is the signal . IQ data has extensive use in many signal processing contexts, including for radio modulation, software-defined radio, audio signal processing and electrical engineering.
Also, there is no audio local oscillator; the injected video carrier serves that purpose. Analogue television receivers using system B and similar systems: 33.4 MHz for the aural and 38.9 MHz for the visual signal. (The discussion about the frequency conversion is the same as in system M.)
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 ...
In such a radio receiver, a local oscillator (LO) is used to heterodyne or "beat" against the incoming radio frequency (RF), generating sum and difference frequencies. One of these will be at the intermediate frequency (IF), and will be selected and amplified. The radio receiver is responsive to any signal at its designed IF frequency ...