RF ELECTRICAL PROPERTIES OF BITUMINOUS COAL SAMPLES

Abstract

In order to estimate the transparency of coal in place to radio waves in the VHF range, some preliminary measurements were made on freshly collected samples of two bituminous coals. A capacitance test cell and an RF impedance bridge were used. The dielectric constant was found to be fairly uniform, ranging between about 2 and 4 for all frequencies. The RF losses were equivalent to a resistivity in the range of 500 to 2000 ohm‐m at 100 Mhz. Equivalent resistivities at lower frequencies were greater, roughly inversely proportional to frequency. These coals would carry 100 Mhz waves over distances of the order of 50 m with 60 db of attenuation, and 1 Mhz waves, for 1 to 10 km. However, the clay and pyrite veins occurring in the Pittsburgh coal bed, where they are large and numerous, may well obstruct radio waves (especially of horizontal polarization).