HP 416A - Page 34

3. On the Model 416A, set the RANGE switch at 0 DB 100%.
There is a short across the line , and therefore there now exists a
condition of 100% reflection. Essentially , the following signals are
entering the Model 416A : at the REFLECTED/PROBE input, a volt-
age proportional to the 100% reflection; at the INCIDENT /REFERENCE
input: ( 1) a voltage proportional to the incident power, and (2) an
error signal proportional to the reflection from the load.
4. Adjustment of the Model X920A adjusts the phase of the reflection
from the short and therefore the phase of the error signal.
Adjust the Model X920A to obtain ( 1) a maximum indication on the
Model 416A meter, and (2) a minimum indication.
Referred to the reflected detector , the change in phase of the error
signal may be considered to be adding to or subtracting from the re-
flected voltage to give a maximum and a minimum reflection coef -
ficient reading.
5. Note the maximum and minim.um readings, and determine the differ-
ence between the two .
For example, if the maximum indication is 99% and the minimum is
95%, there is a 4% difference.
6. To calibrate the system for 100% reflection , so adjust the SET TO
FULL SCALE control on the Model 416A that the midpoint of the max-
mm difference would be a 100% meter indication.
For example, for the readings given above , the minimum indication
should be 98% and the maximum , 102%. Though the adjustment
may be made at either the max or min end, since 102% is off the scale
and would have to be approximated , it is suggested that the adjustment
of the SET TO FULL SCALE control be made when the short is in the
position where the minimum reading occurs.
a. Adjust the Model X920A to obtain the minimum indication, 95%.
b . On the Model 416A, adjust SET TO FULL SCALE to bring this
minimum indication up to 98% .
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