EMC — Reference Tool
Four separate plots corresponding directly to Appendix A, Figures A-5 through A-8. They compare a traditional scanning receiver with an FFT receiver for the standard's example signal: one 10 µs, 0.1 V pulse every second.
A 1 Hz pulse train has a one-second repetition period. A traditional receiver moves its narrow bandpass through the spectrum, so individual pulses are caught only at the frequencies inside the bandpass when each pulse occurs. A longer scan catches the pulse at many more frequency positions. An FFT receiver observes a complete frequency block at once: if its time record catches the pulse, it produces the continuous spectral profile; if not, the whole acquisition can miss it.
For 10 kHz to 150 kHz, MIL-STD-461G Table II specifies a 1 kHz, 6 dB resolution bandwidth, a 15 ms dwell for a stepped-tuned receiver and a 1 s dwell per FFT measurement bandwidth. The longer FFT record is deliberate: the Appendix example shows that 15 ms gives only a 1.5% chance of intercepting a pulse that occurs once per second.
Minimum scan example used by the Appendix.
Several isolated responses are captured. The bandpass crosses only a small part of the spectrum when each one-second pulse occurs, leaving gaps between detected portions.
The slower scan samples the pulse at far more frequency positions.
The responses overlap into the spectral profile. The additional scan time improves the chance of intercept at every part of the span, but at a large time cost.
A complete frequency block is observed for only 0.015 s.
The pulse is missed in this acquisition. The receiver has frequency coverage, but not enough time coverage for a once-per-second event.
The time record covers a complete pulse repetition period.
The continuous spectral profile is captured. One compliant time record covers the entire frequency block and includes at least one event from a periodic 1 Hz source.
These are original, illustrative recreations of the behaviour described by MIL-STD-461G Appendix A, not copied standard figures and not simulated receiver calibration data. The CE102 115 V limit is included for orientation. Use the controlled standard and the verified settings of the actual measurement receiver for formal work.