Dealing with Radio Frequency Interference

Fig. 1: Power level in the 1.5-2.0 GHz band for antenna 3 in the direction of strongest RFI. The black curve is the band power spectrum with noise diode turned off. The black horizontal line is the median power over the band (taken to be representative of the non-RFI power level). The gray curve is the band power spectrum with the noise diode turned on. The gray horizontal line is the corresponding median power.

Fig. 2: Power level in the 1.5-2.0 GHz band for antenna 3 in the direction of weakest RFI. The curves are the same as in Fig. 1.

The EOVSA system has been designed to work over the entire range 1-18 GHz. However, the cell-phone band near 2 GHz has gotten worse over time in the valley, and when testing of the new front ends began, we immediately found serious problems with Radio Frequency Interference (RFI) causing non-linearities in the system, particularly the optical link. This was especially problematic when pointing in the SW direction in the afternoon, but was basically unacceptable over the entire sky. Although we were aware of the problems between 1940-1980 MHz (see Figures 1 and 2),