Receiver gain calibration for radio observations at the Waseda Nasu Pulsar Observatory

We have started programs at the Waseda Nasu Pulsar Observatory to identify EGRET γ-ray sources and to search for radio transients. The observed frequency was 1.4 ± 0.01 GHz, and eight-element spherical dish antennas were used as four pairs of interferometers, with each element 20 m in diameter. The observable region was ±5° from zenith, covering a region of sky 32° ≤ δ ≤ 42° in declination. For accurate flux measurement, we developed a receiver gain calibration system using Johnson-Nyquist noise; the system was compact, inexpensive, and easily maintained. We describe the system and recent results of radio source monitoring.