Tektronix SPG8000A, User Manual

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114 SPG8000A User Manual
All instrument zone plate patterns are defined with coefficients of ten
parameters that correspond to the constants in the above equation. While the
possibilities are virtually endless, most common zone plates are defined with
only one or two parameters, while the coefficients of the remaining parameters
are kept at zero.
The instrument generates six standard zone plate signals: circle frequency,
diagonal frequency, horizontal sine frequency, horizontal sweep frequency,
vertical sine frequency, and vertical sweep frequency. Each standard zone
plate signal has a pattern control parameter. (See Table 41 .) This pattern
control parameter is unique to the zone plate signal it is associated with.
When you first enter the zone plate parameters menu for a signal, the pattern
control parameter for that signal is displayed. The pattern control parameter
controls the basic pattern frequency by adjusting the dependent parameters.
For example, if you change the Circle Frequency, the generator adjusts four of
the dependent parameters to keep the circle round.
Table 41: Zone plate pattern control parameters
Zone plate
signal Pattern control parameter Parameter definition
Circle Circle Frequency (maximum c/aph) The circle frequency is actually the equivalent of the
maximum vertical sinusoid frequency at the very top
and bottom of the screen (see the discussion of the K
Y
2
parameter). Adjusting the circle frequency has the simple
effect of increasing or decreasing the maximum frequency
at the outer edges of the pattern. However, this adjustment
actually changes the coefficients of four of the zone plate
parameters to keep the pattern round and centered on the
screen.
Diagonal
Diagonal Frequency (equivalent c/aph)
The diagonal frequency is times the vertical and
horizontal frequencies (c/aph). Adjusting the diagonal sine
frequency changes both the KX and KY coefficients.
H Sine Horizontal Frequency (MHz) The horizontal frequency reported on the display is the real
time frequency of the sine wave that causes the vertical
bar pattern. The maximum frequency is half of the clock
frequency used by the generator for the active video
standard (for example, 74.25 MHz/2 = 37.125 MHz).
H Sweep H Sweep Frequency (maximum MHz, or For horizontal sweep frequencies up to half of the video
multiple) standard’s sampling frequency, f
s
, the displayed value is the
maximum (or swept to) frequency of the sine wave. For
numbers greater than f
s
/2, dividing the displayed value by
the sampling frequency will give the number of complete
DC–(f
s
/2)–DC cycles per line. For example, in a standard
with sampling frequency of 74.25 MHz, a horizontal sweep
frequency of 148.5 MHz will result in approximately two
complete frequency sweeps across the picture.