Boonton 4540 Peak Power Meter User Manual - Manual (Page 237)

Boonton 4540 Series RF Power Meter
Application Notes 6-9
7. The process locates the bottom amplitude (baseline) using the IEEE histogram method. A histogram is
generated for all samples in the lowest 12.8 dB range of sample values. The range is subdivided into 64
power levels of 0.2 dB each. The histogram is scanned to locate the power level with the maximum number
of crossings. This level is designated the baseline amplitude. If two or more power value have equal counts,
the lowest is selected.
8. The process follows a similar procedure to locate the top amplitude (top line). The power range for the top
histogram is 5 dB and the resolution is 0.02 dB, resulting in 250 levels. The level-crossing histogram is
computed for a single pulse, using the samples which exceed the transition threshold. If only one transition
exists in the buffer (Types 2 and 3), the process uses the samples that lie between the edge of the screen and
the transition threshold (See Figure 6-6). For a level to be designated the top amplitude, the number of
crossings of that level must be at least
1 ¤16 the number of pixels in the pulse width; otherwise, the peak
value is designated the top amplitude.
9. The process establishes the proximal, mesial, and distal levels as a percentage of the difference between top
amplitude and bottom amplitude power. The percentage can be calculated on a power or voltage basis. The
proximal, mesial, and distal threshold values are user settable from 1% to 99%, with the restriction that the
proximal < mesial < distal. Normally, these values will be set to 10%, 50% and 90%, respectively.
Figure 6-6.
Time Interpolation
10. The process determines horizontal position, in pixels, at which the signal crosses the mesial value. This is done
to a resolution of 0.1 pixel, or 1/5000 of the screen width. Ordinarily, the sample values do not fall precisely on
the mesial line, and it is necessary to interpolate between the two nearest samples to determine where the mesial
crossing occurred. This process is demonstrated in the example above (Figure 6-6):