HP 8414A Operating And Service Manual page 15

Model 8414А
75
е
. n . 7 . ADMITTANCE POINT
9 Е 115 «10.77
x. JN x . > 22. >
|
or- 222224.
|
IMPEDANCE POINT
Figure 3-4. Smith Chart Plot of Admittance Point
ized admittance may be read directly from the
graph. In Figure 3-4 the normalized admittance
value is 1.15 + j0.77.
3-24. Alternate Smith Chart Overlays.
3-25. Twelve different Smith Chart overlay graphs
are furnished with the Polar Display. There are
three graph styles in the Smith Chart overlays; a
standard graph, an expanded graph and a com-
pressed graph (refer to Figure 3-5). There are four
overlays for each of the graph styles, two for view-
ing and two with parallax correction for photo-
graphing. There is a clear overlay and an opaque
overlay for viewing, a clear and an opaque overlay
for photographing. The opaque overlays mask the
internal graticule so only the overlay lines are vis-
ible.
3-26. Standard Smith Chart Overlay. When a
standard Smith Chart overlay is installed on the
face of the CRT, the standard calibration of the
Polar Display provides the correct scaling factor for
the Smith Chart. Scaling factors for the expanded
and compressed chart overlays are computed from
the standard calibration of the Polar Display.
Adjustment of the test channel gain for the
expanded and compressed graphs is explained in
the following paragraphs.
Section III
Operation
3-27. Expanded Smith Chart Overlay. The ex-
panded Smith Chart enlarges the center of the
standard Smith Chart to full scale so that the
region close to 50 ohms can be analyzed in detail.
When the expanded Smith Chart is installed on the
СКТ, the gain of the Network Analyzer test chan-
nel amplifier must be increased by 14 dB to match
the scale of the overlay. This is accomplished by
first noting the calibration setting of the test chan-
nel gain! controls on the Network Analyzer for the
standard Smith Chart. This calibration value is
added to 14 dB and the total value is set at the test
channel gain! controls.
3-28. Compressed Smith Chart Overlay. The
compressed Smith Chart overlay provides a display
in the negative-real impedance region. When the
compressed Smith Chart overlay is installed on the
CRT, the gain of the Network Analyzer test-
channel amplifier must be decreased by 10 dB to
match the scale of the overlay. This is accomp-
lished by first noting the calibration setting of the
test channel gain' controls on the Network Ana-
lyzer for the standard Smith Chart. Ten dB is then
subtracted from this calibration value and the
resultant number is set at the test channel gain
controls! .
3-29. Marking Frequency on the Display.
3-30. A rear-panel marker INPUT connector ac-
cepts dc frequency-marker pulses from the Sweep
Oscillator. Markers appear on the trace as bright
spots. This allows measurements to be made at
specific frequencies on a broadband display.
3-31. Display Blanking.
3-32. Blanking pulses from HP 690 and 8690
series Sweep Oscillators may be applied to a rear-
panel blanking input connector blanking the CRT
during sweeper retrace. A blanking signal is also
obtained from the 8410A Network Analyzer main-
frame. The 8410A Network Analyzer automati-
cally produces a blanking signal whenever it is not
tuned to its input signals. This blanking signal is
fed internally to the 8414A. The 8407A main-
frame does not produce this second form of blank-
ing.
3-33. Increased Accuracy for Reflection Measure-
ments by Minimizing Directivity Errors.
3-34. Directivity errors become significant in the
measurement of small reflection coefficients, but
the error can be calibrated out at single frequen-
lpisplay reference for 8407A
3-5