HP 416A - Page 33

NOTE : If greater accuracy is desired , at this time follow the procedure
described under Adjustment of Slide Screw Tuner , below,
6. On the Model 416A :
b .
In single - frequency operation , wit h a short across the line , SET TO
FULL SCALE may be adjusted to obtain a meter indication of
exactly 100%.
Calibration at Single Frequency with Slid i ng Short
By using a sliding short which varies the phase of the 100% reflection
during calibration , it is possible to detect the magnitude of an error signal which is
proportional to the reflected voltage. By calibrating while using a sliding short, the
possibility of doubling the error is avoided
0
(Since the error being compensated
for is in proportion to the reflecte d voltage . if a fixed short happened to be so
placed that the phase of the reflected voltage was 180° out of phase with that of
the incident voltage while SET TO FULL SCALE is being adjusted, the error
could be doubled o)
When a reflectometer system is calibrated while using a sliding short,
and the directivity error signal also is canceled (by use of a slide screw tuner and
moving load) , the reflectome ter system will be adjusted for measurements of
maximum accuracy . At the frequency at which the system is calibrated , meas -
urements will be accura t e within ±0 005 for reflection c oefficients below 0 , 3.
To calibrate with a sliding short , such as a Hewlett - Packard Model X902A
Adjustable Short , proceed as follows :
1. On the Model 670H (or HM)
a. Se t the FREQUENCY - KMC d ia l for the desired frequency .
b .
Set the SELECTOR switch at the MANUAL position .
c. Adjust the ATTENUATION control whi le watching the tuning eye
on the Model 416A. The ATTENUATION control should be ad -
justed to obtain an approximately 1 /8
11
gap in the tuning eye
shutter .
NOTE : For maximum accuracy, at th i s time follow the procedure de -
scribed under Adjustment of Slide Screw Tuner, below.
2. Disconnect the load , an d in its place connect a sliding short such as
a Model X920A Adjustable Sho rt.
NOTE : If a slide screw tuner has been adjusted to cancel the directivity
error, connect the sliding short to the slide screw tuner, as in -
dic ated in Fig . 12 - 1. DO NOT DISTURB the adjustment of the
slide screw tuner.
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