PMX40 RF Power Meter – INSTRUCTION MANUAL
5-9
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 5-6.
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 5-6):
Item
dBm
mW
Mesial value 10.0
10.0
Sample n
8.0
6.3
Sample n+1
11.0
12.6
The interpolated crossing time, t
x
, is calculated from:
𝑡𝑡
𝑥𝑥
=
𝑡𝑡
𝑛𝑛
+
𝑃𝑃
𝑚𝑚𝑚𝑚𝑠𝑠
− 𝑃𝑃
𝑛𝑛
𝑃𝑃
𝑛𝑛+1
−
𝑃𝑃
𝑛𝑛
where P is in watts and n is the number of the sampling interval, referenced to the trigger event. For this
example
𝑡𝑡
𝑥𝑥
=
𝑡𝑡
𝑛𝑛
+
10.0
−
6.3
12.6
−
6.3
𝑡𝑡
𝑥𝑥
=
𝑡𝑡
𝑛𝑛
+ 0.6
