Spectra of OVRO-LWA signals at correlator: predicted vs. observed

The variation with frequency of the power spectral density (PSD) of OVRO-LWA signals is significantly different than expected within the 25-85 MHz observing band, both for the core antennas (coax-connected) and the expansion antennas (fiber-connected). We observe that the peak of the spectrum is at 33 MHz and the minimum is at 85 MHz; this much is as expected. At the antenna (front end output), the ratio of PSDs at these frequencies is predicted to be 8.1 dB. At the correlator, it should be the same for fiber-connected antennas, and it should be 9.6 to 18.2 dB for coax-connected antennas, depending on cable length. We actually observe a much steeper dropoff. The range is 11.1 to 17.7 dB for fiber-connected antennas (median 14.7 dB) and 11.4 to 20.7 dB for coax-connected antennas (median 18.6 dB).