RFI Environment at the OVRO LWA: Quantitative Measurements

Abstract

Measurements of the power spectral density of signals received by a few selected OVRO LWA antennas were collected for at least 24 hours over the frequency range 0 to 165 MHz. The objective was to quantify the RFI environment, concentrating primarily on the signals outside the target observing band of 25 to 85 MHz. Those out-of-band signals are subject to suppression by filtering. Significant filtering is practical only after the signals are delivered to the processing shelter, so these results can be used to set the dynamic range requirements for the RF-over-fiber links from outer antennas and for the pre-filtering analog signal processing at the shelter, as well as the amount of filtering needed to keep the signals within the dynamic range of the digitizers. It is found that the total power below 20 MHz (HF communication) is highly variable with peaks about 16 dB above the total power in the observing band, and that the total power above 88 MHz (primarily FM radio) is very stable at about 29 dB above the minimum power in the observing band. Sporadic in-band RFI is also seen.

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