The applet models the performance of limiting amplifiers across the limiting region. Compression effects on signal and noise, both in-phase and quadrature, are covered.
There are three plot options from the drop-down menu, plot 1 shows Total Power, Signal Power and Noise Power out versus signal Input Power.
Plot 2 shows the more useful SNRO/SNRI versus Input Power.
In the first power plots, the black curve shows the total output noise power resulting from the effective input noise power (kTB_rF) as the signal varies across the dynamic range defined by the Input Power range text boxes. The magenta and orange curves show the in-phase and quadrature output noise components.
At very low input signal levels, the output power is mainly noise, and the two noise components are equal.
At high signal levels, well into compression, the output noise power is largely due to the quadrature component, and the in-phase component is seriously compressed.
In the second drop-down menu plot set, the two main curves are Total SNRO/SNRI (blue curve) and Quadrature SNRO/SNRI (red curve).
At negative (dB) SNRs (signal < noise), the signal is suppressed by an amount dependent upon how hard the noise drives the amplifier into compression up to a maximum of about 1 dB.
At large positive SNRs, the in-phase noise is suppressed and the output SNR shows a 3-dB improvement (note that the output SNR and quadrature SNRs become equal).
The two curves moving from bottom left to top right are the in-phase (cyan) and quadrature (gray) vector SNRs at the video output of an IFM discriminator at the limiter output.
On the upper right hand side of the display, also following the mouse x-axis input power, is listed the IFM video SNR values. Scrollbars control the video bandwidth and line delay. Square-law detector and interferometer performance is modeled when the line delay is zero and 100 ns, respectively.
To retain a mouse reading at a selected input RF power, left-click and drag off screen.
The third drop-down menu option, displays the IFM SNRs as a function of the limiting amplifier gain for a set signal input (bottom scrollbar).
The interesting point to note in this plot is that there appears to be an optimum gain to enhance the quadrature (angle SNR) at useful minimum receiver threshold levels. Moving the mouse in plotted region, displays the plot data referred to the x-axis mouse position.
Out-of-Range is indicated when parameter values are selected which are out of the computable range - usually due to excessively high input SNR.

User Notes:
The limiter maximum output power is 0 dBm. Once the gain and input noise are sufficient to saturate the amplifier, increasing the limiter small-signal gain has little effect on the mean output signal power. It is interesting to note that in this condition, the output signal power becomes a measure of the input SNR.
To analyze how different modulators perform across the limiting region, the demodulator in-phase and quadrature noise responses can be weighted using the plotted noise power compression values.