The applet investigates the pulse threshold triggering characteristics of various receivers.
Signal pulse amplitude is variable, as is receiver threshold level. Artificial sinusoidal noise is added to the signal at a notional level which allows TSS to be visualized.
The oscilloscope-type presentation is continuously signal-normalized in amplitude for clarity, but the time base is user-adjustable.
The upper display shows the detection and fallback probabilities along the pulse corresponding to the threshold setting, signal level, and the hysteresis setting. The hysteresis is set relative to the signal level. These upper curves indicate the cumulative probability along the pulse and clearly demonstrates that, for sub-threshold pulses, the most probable point of detection is towards the end of the pulse. Also, once detection has occurred, the probability of fallback also increases with pulse duration. It is this finite probability of pulse truncation which is responsible for poor pulse width measurement around threshold.
By adjusting the Threshold and Signal Level scrollbars in the lower display, the useful detection probability ranges for the six receiver types in the drop-down menu can be evaluated.
SNRO is the output SNR in the presence of a signal, and TNR is signal-equivalent threshold-to-no-signal ratio.
Default values may be modified and the display updated using the scrollbars or the keyboard Enter/Return key.
Moving the mouse in Signal power-Time space displays the pointer values, whereas in the Probability-Time space the plotted probability values are displayed.
All receiver results assume rectangular-shaped RF and video passbands and sufficient RF gain to ensure that following noise contributions are swamped.

User Notes:
When selecting the compressive receiver, the DDL Delay (Dispersive Delay Line) scrollbar is displayed. Adjustment modifies the processing gain or compression ratio BT where, B is the DDL bandwidth (= RF Band) and T is the DDL delay. The video bandwidth is set at half the RF bandwidth. The signal pulse width should be equal to or greater than the DDL delay to realize the full DDL processing gain. The compressed output pulse is short (1/B) and it may be necessary to adjust the Timebase scrollbar.
For wideband RF amplifier detector video receiving systems, both probability of detection and system false-alarm rate on a pulse detection basis can be controlled by suitable choice of the system threshold setting.
A system threshold of 16 dB (equivalent to a signal level of -68 dBm for the RF amplifier DV receiver example) will ensure around 95% probability of triggering the threshold after 0.2 μs at a 16 dB signal-to-noise ratio with 2% probability of falling back before the end of a 1μs pulse.
There is a negligible probability of false alarms in the absence of signals. A signal 1.5 dB lower has only a 30% probability of triggering by the end of the pulse and could be severely truncated. It is usual therefore to set thresholds somewhat higher than this by some 2 to 3 dB in order to minimize the uncertainty region and to ensure that good parameter measurement accuracy occurs on signals at threshold.