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 occuring in the Pittsburgh coal bed, where they are large and numerous, may well obstruct radio waves (especially of horizontal polarization).

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