Mode | Symbol Rate | Typing Speed | Bandwidth |
RTTY 45 | 45.45 baud | 6.0 cps (60 wpm) | 270 Hz |
RTTY 50 | 50.0 baud | 6.6 cps (66 wpm) | 280 Hz |
RTTY 75 | 75.0 baud | 10.0 cps (100 wpm) | 370 Hz |
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W1AW on air signal | AFSK signal | Spectrum |
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Image A Transceiver operated in FSK mode Power: 100 W |
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Image B Transceiver in USB, fldigi AFSK audio drive Space at 2125, Mark at 2295 Hz Power: 100 Watts, ALC just extinguished |
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Image C Transceiver in USB, fldigi AFSK audio drive Space at 2125, Mark at 2295 Hz Power: reduced to 80 Watts (-1 dB) |
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Image D - 2 K span Transceiver in USB, fldigi AFSK audio drive Space at 2125, Mark at 2295 Hz Power: reduced to 70 Watts (-1.5 dB) |
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Image F - 10 K span Transceiver in USB, fldigi AFSK audio drive Space at 830 Hz, Mark at 1000 Hz Power: 70 Watts. The LSB leakage is clearly seen at approximately -55 dB |
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Image G - 5 K span Transceiver in USB, fldigi AFSK audio drive Space at 830 Hz, Mark at 1000 Hz Power: 70 Watts. The LSB leakage is clearly seen at approximately -55 dB. |
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Image H - 2 K span Transceiver in USB, fldigi AFSK audio drive Space at 830 Hz, Mark at 1000 Hz Stop Bits set to 2 vice 1.5 Power: 70 Watts. Compare this to image D |
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The mark and space signals are
converted to base band and then filtered in a low pass filter.
Each filter is a variant of Chen's enhanced Nyquist filter. It is
implemented using a Fast Overlap-and-Add Fourier Transform. Each time the baud rate is selected the program must "rebuild" the digital RTTY filter. The filter parameters are optimized for the baud rate. The detector is an optimized Automatic Threshhold Correcting (ATC) type described in Chen's paper. |