HP 8642A Operation And Calibration Manual page 284

Performance Tests
4-34
Model 8642A/B
PERFORMANCE TESTS
7. Low Level SWR, Return Loss Calculation
In each row in the preceding table compute the "Actual" return loss
using the following formula:
"Ref." - "Reflected"
=
"Actual"
Verify that "Actual"
is
greater than the specified Min.
NOTE
It
you wish to compute the actual SWR from the
return loss at each frequency, you may use the
following formula:
SWR
1
+
[lO-(Retum
Lo •• (20)]
1 [lO-(Retum
Los.(20)]