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Detection of Blink or Off Air

Detection of Blink or Off Air. Requirements Detect OOT warning to meet 10 sec time to alarm Retain present blink system to allow CG watchstander to bring station on air & then verify signal is within tolerance Questions Can present blink system meet time to alarm requirements?

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Detection of Blink or Off Air

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  1. Detection of Blink or Off Air • Requirements • Detect OOT warning to meet 10 sec time to alarm • Retain present blink system to allow CG watchstander to bring station on air & then verify signal is within tolerance • Questions • Can present blink system meet time to alarm requirements? • If not, how long of an off air is required before bringing station back on air w/blink? • Propose approx 10 sec so that receiver knows not to use signal when it returns • If being brought back w/o blink, no minimum off air time. However, if off air time exceeds some threshold (5 sec?), receivers will not be able to use signal until they verify it is not blinking. • No minimum blink time.

  2. Detection of Blink or Off Air • Analysis • Test statistic is I^2 + Q^2 re nominal • Statistics are chi square with 2 degrees of freedom • Non centrality parameter for normal on-air condition • x 1/16 for blinking condition • No non centrality parameter for off-air condition • Rectangular vice exponentially decaying window • Threshold set for specified Probability of False Alarm • Probability of False Alarm (Pfa) is continuity issue • Would like to do analysis at Pfa = 1e-7 or 1e-8, but numerical problems in MatLab algorithms for chi square distributions do not allow. • SNR in 30 kHz NEBW, after credit for clipping, before credit for antenna directionality • May look at narrower band channel for blink/off-air detection

  3. Detection of Blink or Off Air • Conclusions • Off-air can be detected in sufficient time, blink cannot • 8 dB SNR difference for same Pfa & integration time • Narrower band RF channel for blink detection could recover some of this difference, but not enough • Need to specify Pfa to meet continuity requirement • May need to do approximations for lower Pfa • It appears to go from 1e-6 to 1e-7 is about 0.5dB, etc. • Need to retain present blink system to permit CG to bring station on air & then verify signal in tolerance

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