Tektronix AWVG1, User Manual

Page: 90 / 116

Appendix C: Zone Plates
C- 2
AWVG1 Wideband Video Generator User Manual
follows from the phase of the cycle at that point. By the definition of a zone
plate, the phase of any point is determined by the following equation:
Φ
xyt
=
k
Φ
+
k
X
( x )
+
k
Y
( y )
+
k
T
( t )
+
1
2
k
X
2
(
x
2
)
+
1
2
k
Y
2
(
y
2
)
+
1
2
k
T
2
(
t
2
)
+
k
XT
( xt )
+
k
YT
( yt )
+
k
XY
( xy )
where x , y , and t are the coordinates of the point in question and
k
Φ
,
k
X
,
k
Y
,
k
T
,
k
XT
,
k
YT
,
k
XY
,
k
X
2
,
k
Y
2
, and
k
T 2
are constants.
Zone Plate Parameters
You define zone-plate patterns in the AWVG1 Generator module using coeffi-
cients of ten parameters that correspond to the constants in the preceding
equation. Although the possibilities are virtually endless, most common zone
plates are defined with only one or two parameters, with the coefficients of the
remaining parameters kept at zero.
The zone-plate parameters are discussed in the order that they appear in the zone
plate Parameters window. The adjustment range of most of the coefficients
depends on the characteristics (sample frequency and lines per field) of the active
video standard.
TG 200 display:
Circle Frequency
Diag. Frequency
Horz. Frequency
H. Sweep Frequency
Vert. Frequency
V. Sweep Frequency
Each standard zone plate signal has a pattern control parameter. The AWVG1
Generator module generates six standard zone plate signals; circle frequency,
diagonal frequency, horizontal frequency, horizontal sweep frequency, vertical
frequency, and vertical sweep frequency. The standard zone plate signals are
discussed in more detail on page C--9.
In the Zone Plate Parameters window, the pattern control parameter appears at
the top of the list, followed by dependent (indented) parameters. The pattern
control parameter controls the basic pattern frequency by adjusting the dependent
parameters. If you adjust one of the dependent parameters individually, the
pattern control parameter will become invalid. In Figure C--2, the zone plate
Parameters window shows the 625 Bullseye signal (selected through the Test
Pattern Control Parameter