Given that the hopper’s frequency spacing is known from searching the frequency range, a receiver can be fixed tuned to one of the hop channels. The FH transmitter is then detected when its instantaneous frequency coincides with the set receive frequency. For a hop to be detectable its duration must be Th > Ti. In wait mode (hopper trap) the time required for synthesizer setting and signal processing does not influence probability of intercept, so Td = Ti applies in this case.
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