| 摘要 |
A low frequency air-to-air and air-to-ground communication system is described. The propagation characteristics of low frequencies and very low frequencies are such that less signal attenuation is encountered at intercontinental ranges when the system is operating in the TE mode as compared to the TM mode. The TE mode is defined as having a dominant vertical magnetic field component and the TM mode is defined as having a dominant vertical electric field. Also, the receiver in an aircraft is subjected to less ambient noise when it is positioned to receive the TE mode. However, ground transmitters are inefficient at transmitting and receiving the TE mode because the ground image tends to cancel out the transmitted and received signals. The apparatus described herein comprises a transmitter and receiver having horizontal electric current loop or linear horizontal antennas to generate and receive TE mode transmissions, said antenna being mounted on aircraft at an altitude of at least one quarter of a wave length above the earth's surface to enable efficient transmission and reception. A noise cancelling circuit for removing undesired signals at the receiver is also described.
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