Frequency Sources and Control

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Communication receivers are seldom single-channel devices, but more often cover wide frequency ranges. In the superheterodyne receiver, this is accomplished by mixing the input signal with an LO signal. The LO source must meet a variety of requirements: a) It must have high spectral purity, b) It must be agile so that it can move rapidly (jump) between frequencies in a time frame that can be as short as a few microseconds, and c) the increments in which frequencies can be selected must be small. Frequency resoultion between 1 and 100 Hz is generally adaequate below 30MHz; however, there are a number of systems that provide 0.001-Hz steps. At higher frequencies, resolution is generally greater than 1 kHz. In most modern receivers, such a frequency source is typically a synthesizer that generates all individual frequencies as needed over the required frequency band. The modern synthesizer provides stable phase-coherent outputs. The frequencies are derived from a master standard, which can be a high precision crystal oscillator, a secondary atomic standard (such as a rubidium gas cell), or a promary standard using a cesium atomic beam. The following charteristics must be specified for the synthesizer: frequency range, frequency resolution, frequency indication, maximum frequency error, settling time, reference frequency, output power, harmonic distortion, SSB phase noise, Discrete spurs, wide-band noise, control interface, power consumption, mechanical size, envirinmental conditions.

In this talk, speaker will discuss design of synthesizer for the applications in moderm communication systems

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2:00PM-3:00PM: Talk You don't have to be IEEE member to attend the talk.

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