Boonton 4500B Peak Power Meter Manual do Utilizador descarregar pdf (Página 330)

Boonton 4500B RF Peak Power Analyzer

Application Notes

6-20

The sensor calfactor uncertainty is due to uncertainties encountered while performing this frequency calibration (due

to both standards uncertainty, and measurement uncertainty), and is different for each frequency. Both worst case

and RSS uncertainties are provided for the frequency range covered by each sensor, and are listed on the sensor

datasheet and in the Boonton Electronics Power Sensor Manual.

If the measurement frequency is between sensor calfactor entries, the most conservative approach is to use the

higher of the two corresponding uncertainty figures. It is also be possible to estimate the figure by linear

interpolation.

If the measurement frequency is identical to the AutoCal frequency, a calfactor uncertainty of zero should be used,

since any absolute error in the calfactor cancels out during AutoCal. At frequencies that are close to the AutoCal

frequency, the calfactor uncertainty is only partially cancelled out during AutoCal, so it is generally acceptable to

take the uncertainty for the next closest frequency, and scale it down.

6.5.3 Sample Uncertainty Calculations. The following example shows calculations for a peak power sensor, Model

56518. The figures used in this example are meant to show the general technique, and does not apply to all

applicat

is not an exact science, and requires some understanding of your specific measurement conditions.

Typical Example: Model 56518 Peak Power Sensor

Model 4500B measurement conditions:

Source Frequency: 900 MHz

Source Power: 13 dBm (20mW)

Source SWR : 1.12 (reflection coefficient = 0.057) at 900 MHz

AutoCal Source: Internal 1GHz Calibrator

AutoCal Temperature: 38C

Current Temperature: 49C

In this example, we will assume that an AutoCal was performed on the sensor earlier in the day, so time and temperature drift

may play a role in the uncertainty.

Step 1: The Instrument Uncertainty figure for the Model 4500B is ±0.20%. Since it has been a while 

use the published figure.

Instrument

= ±0.20%

Step 2: The Calibrator Level Uncertainty for the Model 4500B internal 1GHz calibrator may be calculated from the

. To this figure, we must add 0.03dB or 0.69% per

5dB step from 0dBm. 13dBm is 2.6 5dB steps (13/5) away from 0dBm. Any fraction must always be rounded to the next



CalLevel

= ±(1.51% + (3 × 0.69%))

= ±3.11%

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