Upconverter

An upconverter is an electronic device that shifts the frequency of an input signal upward by mixing it with a local oscillator. By translating a signal from a lower frequency to a higher RF band, upconverters enable transmission over higher-frequency links or compatibility with receivers that operate in the target band. They are the opposite of downconverters, which move signals to lower frequencies.

Typical upconverter architecture includes a mixer, a local oscillator, and RF preselection or filtering stages. The input signal is combined with the LO in a mixer, producing sum and difference frequencies. The desired output is isolated by filters or a selective stage to produce an RF signal in the target band. Some designs employ image-reject techniques or two-stage conversion to suppress unwanted image frequencies and LO feedthrough. The LO frequency is chosen to place the desired channel into the intended transmission or reception band, while maintaining adequate isolation from the LO and other spurious responses.

Applications for upconverters include satellite communications uplinks, where baseband or intermediate-frequency signals are raised to the satellite transmit band; cable television and RF front-ends that map baseband or low-IF content to higher RF channels; and various radio, defense, and test equipment that require RF transmission of lower-frequency signals or digital content.

Key design considerations include conversion gain, noise figure, linearity (IP3), LO leakage, spurii, and phase noise. Proper filtering, shielding, and careful LO planning are essential to minimize image frequencies and unwanted emissions.