Radio signals from air showers at 22 MHz

Abstract

Radio pulses from extensive air showers (EAS) have been observed with a 4 × 4 array of dipoles polarized E–W at a center frequency of 22.25 MHz and an effective bandwidth of 4 MHz. Observations were made simultaneously with antenna beams centered 30 °N and 30 °S of the zenith. The magnetic dip angle being 72°, the north beam faced across the geomagnetic field lines whereas the south beam faced along the field lines. In 600 hours of observation, 1 100 showers were recorded. Two 1-m2 plastic scintillators placed 30 m apart, in coincidence, triggered the cathode-ray-oscillograph recording system.Traces were scanned for 1 μs on either side of the expected location of the radio signals. Background levels were determined by scanning an interval of 0.75 μs, 3.5 μs after the beginning of the trace. Pulses were recorded on both antenna beams. Those on the north-pointing antenna were, on the average, twice as large as those on the south-pointing one. The results suggest that while charge separation in the earth's field is more important than charge excess in generating showers, it is not dominant.