Boonton 4500B Peak Power Meter - Manual (Page 319)

Boonton 4500B RF Peak Power Analyzer
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):