:SPRocess:FFT:DISPlay
Specifies the output format of an FFT operator (:FUNCtion:FOPerator FFT) to be one of the following types:
- Linear Magnitude (
MAGNitude) - dBV (
DBV) - dBm (
DBM) - Phase (
PHASe) - Unwrapped Phase (
UPHase) - Group Delay (
GDELay)
When phase (PHASe), unwrapped phase (UPHase), or group delay (GDELay) is selected, use the :FFT:PREFerence command to set the FFT phase reference to left, center, or manual. If you select manual, use the :FFT:PREFerence:TORigin command to enter the FFT origin in seconds.
If the input is an optical signal and dBV (Electrical) is selected, use the :FFT:TFACtor command to enter the voltage conversion factor (V/W).
To ensure that enough data is available to construct a useful FFT, set FlexDCA's timebase scale equal to the waveform's period. This will display 10 waveform cycles. For example, for a 5 GHz (200 ps) reference clock, enter a scale setting of 200 ps/division.
Content Windows
The FFT waveform is automatically displayed in the appropriate type of content window, which is listed in the following table and displayed in the above picture. For the MAGNitude, PHASe, and GDELay arguments, you can optionally move the waveform to an additional content window of the same type using the :FUNCtion{1:64}:CWINDdow command. For example,
:FUNCtion1:FOPerator FFT // Create an FFT function. :FUNCtion1:OPERand1 CHAN1A // Assign input waveform. :SPRocess1:FFT:DISPlay GDELay // Select output waveform type. Waveform is automatically assigned to content window GDELay1. :FUNCtion1:CWINdow GDELay2 // Display content window GDELay2 (Delay 2) and re-assign output waveform from GDELay1 to GDELay2.
When MAGNitude is selected, the waveform is displayed in a Waveform waveform content window. To view the FFT waveform, turn on pattern lock (:TRIGger:PLOCk ON) so that a single-valued waveform is provided as the function's input. In Eye mode, if the entire pattern is acquired (:ACQuire:EPATtern ON), additionally turn waveform wrapping off (:ACQuire:WRAPping OFF).
| Argument | Equivalent GUI Selection |
Displayed Content Window |
Number of Available Windows |
Scale Units | |
|---|---|---|---|---|---|
| Via Front Panel |
Programmatically | ||||
| MAGNitude | Linear Magnitude | Waveform | 1 | 1 | Y-Axis: Volts or Watts (linear scale) X-Axis: seconds |
| DBV | dBV | Magnitude | 1 | 4 | Y-Axis: dB (logarithmic scale) X-Axis: Hertz |
| DBM | dBm | ||||
| PHASe | Phase | Phase | 1 | 4 | Y-Axis: phase (°) X-Axis: Hertz |
| UPHASe | Unwrapped Phase | ||||
| GDELay | Group Delay | Delay | 1 | 4 | Y-Axis: seconds X-Axis: Hertz |
The ability to use waveform content windows was added starting with FlexDCA revision A.03.00.
Example Command Sequence
:FUNCtion2:FOPerator FFT :SPRocess2:FFT:DISPlay DBM :SPRocess2:FFT:WINDow HANNing :FUNCtion2:COLor TCOLor4 :FUNCtion2:DISPlay ON *OPC? … // Your code to synchronize execution timing.