Bird Technologies VPM3 - Manual (Page 53)

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Example - If a source with a 1.50:1 VSWR with the Terminating
Power Sensor was used, which has a max VSWR of 1.20:1, the mis-
match uncertainty would be calculated as follows:

s
1.50 1 –
  1.50 1
+
  
0.200 = =

1
1.20 1 –
  1.20 1
+
  
0.091 = =
MU 1 0.200 0.091

+
  2
1 –
  100
3.67

=

=
If a source with a 1.30:1 VSWR was used instead, the mismatch uncertainty
would be:

s
1.30 1 –
  1.30 1
+
  
0.130 = =

1
1.20 1 –
  1.20 1
+
  
0.091 = =
MU 1 0.130 0.091

+
  2
1 –
  100
2.39

=

=
Using a lower VSWR source can drastically reduce the mismatch uncertainty.
Keep in mind that the typical VSWR of the Model 5011 is 1.03:1, which gives a
much lower mismatch uncertainty.
Example - With the 1.50:1 source, the mismatch uncertainty would
be:

s
1.50 1 –
  1.50 1
+
  
0.200 = =

1
1.03 1 –
  1.03 1
+
  
0.015 = =
MU 1 0.200 0.015

+
  2
1 –
  100
0.59

=

=
To determine the total uncertainty of the measurement, combine the RSS
uncertainty with the mismatch uncertainty using the RSS method. Square the
RSS uncertainty, add it to the square of the mismatch uncertainty, and take the
square root.
Using Example 1 in Table
3 with a source VSWR of 1.50 and a TPS VSWR of 1.20,
the total uncertainty would be:
5.00
2
3.67
2
+ 6.20 percent
 
=
For example 2, the total uncertainty would be 6.82 %.