Boonton 4530 Peak Power Meter User Manual - Manual (Page 162)

Chapter 5 Boonton Electronics
Making Measurements 4530 Series RF Power Meter
5-20
Typical Example #2: Model 57518 Peak Power Sensor
Measurement conditions:
Source Frequency: 900 MHz
Source Power: 13 dBm (20mW)
Source SWR : 1.12 (reflection coefficient = 0.057) at 900 MHz
AutoCal Source: External 2530 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 4530 Series is ±0.20%. Since it has been a while since AutoCal, we’ll
use the published figure.
U
Instrument
= ±0.20%
Step 2: The Calibrator Level Uncertainty for the Model 2530 1GHz external calibrator may be calculated from the
calibrator’s specification. The 0dBm uncertainty is 0.065dB, or 1.51%. 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
highest whole number, so we’re 3 steps away.
U
CalLevel
= ±(1.51% + (3
0 0.69%))
= ±3.11%
Step 3: The Calibrator Mismatch Uncertainty is calculated using the formula in the previous section, using the 2530
calibrator’s published figure for
,
CAL
and calculating the value
,
SNSR
from the SWR specification on the 57518’s
datasheet.
,
CAL
= 0.091 (external 2530 calibrator’s reflection coefficient at 1GHz)
,
SNSR
= (1.15 - 1) / (1.15 + 1) = 0.070 (calculate reflection coefficient of 57518, max SWR = 1.15 at 1 GHz)
U
CalMismatch
= ±2
0 ,
CAL
0 ,
SNSR
0 100 %
= ±2
0 0.091 0 0.070 0 100 %
= ±1.27%
Step 4: The Source Mismatch Uncertainty is calculated using the formula in the previous section, using the DUT’s
specification for
,
SRCE
and calculating the value
,
SNSR
from the SWR specification on the 57518’s datasheet.
,
SRCE
= 0.057 (source reflection coefficient at 900 MHz)
,
SNSR
= (1.15 - 1) / (1.15 + 1) = 0.070 (calculate reflection coefficient of 57518, max SWR = 1.15 at 0.9 GHz)
U
SourceMismatch
= ±2
0 ,
SRCE
0 ,
SNSR
0 100 %
= ±2
0 0.057 0 0.070 0 100 %
= ±0.80%
Step 5: The uncertainty caused by Sensor Shaping Error for a 57518 peak sensor is 4% at all levels, from the sensor’s
datasheet. But since we’re measuring at 900MHz, which is very close to the 1GHz AutoCal frequency, we’ll assume
that the frequency-dependent portion of the shaping error becomes very small, and we’ll estimate that 2% remains.
U
ShapingError
= ±2.0 %