Tektronix SPG8000 Technical Reference page 124

SDI button menu (Option SDI only)
To use a zone plate signal
To modify a zone plate
signal
112
Zone plate signals can be accessed from the SDI button TEST SIGNAL submenu.
(See page 72, SDI TEST SIGNAL submenu.) Here is an example of how you can
use zone plate signals to simplify a common task.
One common task is measuring the horizontal frequency response of a system.
With a typical swept-frequency generator you would apply a signal such as a
1 MHz to 30 MHz sweep with markers every 5 MHz. Then you try to estimate the
frequency of the 3 dB roll-off point by interpolating the position of the 3 dB point
between the markers.
The instrument's adjustable zone plate signal provides a better way:
The H Sweep Zoneplate pattern control parameter is the H Sweep Frequency,
which controls the upper frequency limit of the sweep (the swept-to
frequency).
Simply adjust the H Sweep Frequency until the system roll-off is at –3 dB.
Read the frequency directly from the instrument display.
The H Sine Zoneplate, which provides a constant frequency horizontal sine
signal instead of a swept signal, can be used to reduce error in measuring
attenuation at a given frequency.
Set the Horz. Frequency parameter to a low value and measure the
amplitude of the entire line.
Next, calculate the –3 dB point (0.707 × the low frequency amplitude).
Finally, increase the Horz. Frequency parameter until the system response
for the whole line is at the calculated –3 dB level, and read the –3 dB
frequency directly from the instrument display.
Since the ZP Amplitude parameter is adjustable for each of these signals, you
can measure the response at 100%, 60%, or any other level as needed.
These same techniques can be used to measure vertical or diagonal response, by
selecting the appropriate zoneplate signal.
There are times when a specific test case requires a modified zone plate signal.
By making and saving changes to the zone plate parameters you can create a new
signal that is based on the selected signal, and then save that new signal. Changes
you make affect only the new signal; the standard zone plate signal used as a
basis for the new signal is not changed.
Before making changes, make sure you are familiar with both the zone plate
pattern control parameters and zone plate pattern dependent parameters. (See
page 114, Zone plate pattern control parameters.) (See page 116, Zone plate
dependent parameters.)
SPG8000 Technical Reference