National Radio Astronomy Observatory
نویسنده
چکیده
As part of an initiative to reduce the size, weight, and complexity of radio astronomy receivers and to place the conversion from analog to digital signals as close to the telescope feed as possible, a prototype single-conversion, sideband-separating mixer receiver with a tunable local oscillator (LO) between 5 and 9 GHz has been built and tested. After straightforward gain and phase calibration in digital signal processing, unwanted sideband suppression better than 50 dB is achieved throughout an IF band of ±27 MHz (limited by the sampling speed of the available 14-bit digitizer) and over the full tuning range of the LO. No special phase matching in the analog electronics is required. Calibration vectors can be parameterized in a way that avoids the need for a full two-dimensional (LO and intermediate frequency) measurement matrix. Quantization errors introduced by the digitizer do not degrade sensitivity and sideband suppression as long as the random noise rms voltage is at least 5 sample intervals. The spurious response from the first LO harmonic is about 30 dB down from the fundamental so a switchable low-pass filter at the signal input may be required for operation of the mixer over an LO tuning range greater than about a 1.8:1.
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