Although operation on wavelengths shorter than 200 meters was technically illegal ( but tolerated as the authorities mistakenly believed at first that such frequencies were useless for commercial or military use ), amateurs began to experiment with those wavelengths using newly available vacuum tubes shortly after World War I.

Although operation on wavelengths shorter than 200 meters was technically illegal ( but tolerated as the authorities mistakenly believed at first that such frequencies were useless for commercial or military use ), amateurs began to experiment with those wavelengths using newly available vacuum tubes shortly after World War I.

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