Stanford Research Systems SR780, Руководство по эксплуатации и программированию, Страница: 291 / 497

User Math Menu 4-109
SR780 Network Signal Analyzer
Octave Measurement Group
Swept Sine Measurement Group
Operands are arrays of complex values (real and imaginary). They may be measurement
results (such as FFT(1), Time(1) or Oct(1)), a Trace, or a Constant. An array which is real
simply has zero for its imaginary parts. The array length of an Operand is determined by
the measurement length (number of FFT lines, length of time record, number of octaves,
etc.) or Trace length (length of the data which is stored in the Trace). Constants assume
the length of the user function.
Operands which are measurement results, such as FFT(1) or Oct(1), are exactly the same
as the normal measurements. They are computed from the input data (real time Analog or
capture Playback) and use the frequency and windowing parameters from the menus.
Frequency domain measurements are amplitude calibrated, time records are not. FFT and
Time record measurements are also triggered just like the normal measurements.
FFT(1) and FFT(2) are the FFT of the Ch1 and Ch2 inputs. These operands use the
window chosen in the [Window] menu for the display which is measuring the function.
FFTa(1) is the FFT of the Ch1 input using the window for Display A, regardless of which
display is measuring the function. FFTb(2) is the FFT of the Ch2 input using the window
for Display B. This allows a function to be defined which uses both input channels, each
with a different window. Force-exponential transfer function for example.
FFTu(1) and FFTu(2) are un-windowed FFT’s of the Ch1 and Ch2 inputs.
Octave and Swept Sine measurements are always averaged measurements. Use the
[Average] menu to set the averaging parameters.
Auto_Corr(1), Auto_Corr(2), X_Corr, <F2>/<F1> and Coherence are all averaged FFT
measurements, regardless of whether averaging is On or Off in the [Average] menu. The
Averaging Mode is determined by the definition of the measurement. The Averaging
Type (linear or expo) and the Number of Averages are set in the [Average] menu.
All basic FFT measurements, Time, X_Spec and FFT2/FFT1 are NOT averaged results.
Use the Avg() or VecAvg() operators to perform explicit averaging on these operands.