| 摘要 |
<p>Existing single channel radio teletype circuits employing single frequency shift, i.e. mark/space, are prone to interference from static, impulse type noise, and selective fading. The present invention provides time diversity which improves the error rates of such circuits. A stream of binary coded data is divided into first and second identical data streams. The data in the second stream is delayed by a predetermined number of frames. Subsequently, a comparison of the data in the two streams is made and one-of-four digital signals are produced dependent on the results of the comparison. The one-of-four signals are used to produce corresponding audio tones which are transmitted. At the receiving end, the audio tones are used to produce one-of-four voltages which are processed to produce third and fourth data streams corresponding to the first data stream and the delayed second stream. The third data stream is delayed by the same amount as the second data stream was delayed during transmissions, bringing the third and fourth data streams into correspondence. The better of the two data streams is then selected for use.</p> |
