A long-distance coincidence radio-pulse experiment

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Abstract
Three radio receiving stations, operating at 45, 70, and 70 MHz center frequencies, have been set up for air shower detection. Separations are 10, 12, and 20 km between stations. Pulses are selected by combinations of antennae pointing towards magnetic west at large zenith angles. In 1 000 hours of operation, about 150 events have been observed in excess of the random expectation over the 10-km distance. Over the 12-km separation, no excess has been observed in 244 hours, but operation is restricted in this case by intervening hills to zenith angles less than 84°. Over the 20-km separation, a small excess is observed, which may be due to chance. In a series of subsidiary experiments, radio pulses have been correlated with night-sky Cerenkov detectors and a scintillation counter, and with receivers at 12, 35, and 500 Mc/s. From these experiments the rate of detection of cosmic-ray showers at a single station is believed to be at least 1 per hour, or about 5–10% of the radio pulses selected. Local radio coincidences at individual stations are in excess of random expectation, and the pulse-height spectrum for local events is steeper than would be expected for cosmic-ray events or interference pulses. The long-distance coincidences have not been established directly as cosmic-ray events, but are consistent with this interpretation.

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