Stanford Research Systems SR780, Operating Manual And Programming Reference

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User Math Menu 4-111
SR780 Network Signal Analyzer
View operations ( Mag( ), Mag
2
( ), Phase( ), Real ( ), Imag( ) ) simply convert the
complex operand array into the desired form. Mag( ) and Mag
2
( ) compute the magnitude
(
√
(x
2
+ y
2
)) or magnitude squared (x
2
+ y
2
) with a real result. Phase( ) computes the phase
(tan
-1
( y/x )) unwrapped with a real result. Real( ) simply zeroes the imaginary part.
Imag( ) zeroes the real part.
Conj( ), Ln( ), Exp( ) and Sqrt( ) are defined as follows,
Conj(x + jy) = x - jy
Conj(x - jy) = x + jy
Ln(x + jy) = ln(r) + j
θ
Exp(x + jy) = exp(x) • ( cos(y) + jsin(y) )
Sqrt(x + jy) =
√
r • ( cos(
θ
/2) + jsin(
θ
/2) )
[X/(1-X)] = (x + jy)/(1 - x - jy)
where r =
√
(x
2
+ y
2
) and
θ
= tan
-1
( y/x ). Sqrt computes all angles positive from 0. The
[X/(1-X)]( ) operator is generally used on real arguments only.
The jOmega( ) operator is simply j
ω
and zeroes the real part and fills the imaginary part
with the value of
ω
(2
π
• frequency) at each point in the array. The frequency is
determined by the span of the operand. A measurement operand (FFT(1) or Time(1)) uses
the current frequency span. A Trace operand uses the span of the measurement which is
stored in the Trace.
Not all operations are available in all Measurement Groups. Swept Sine and Octave
measurements have no time records and thus the FFT( ) and IFFT( ) operators are not
available. In addition, the results are always averaged so the Avg( ) and VecAvg( )
operators are also not required. FFT( ), FFTu( ), IFFT( ), Avg( ) and VecAvg( ) are only
available in the FFT Measurement Group.
FFT( ) is the windowed FFT operator. These operations switch the X axis type. The
current window chosen in the [Window] menu is used on the operand before the FFT.
FFTu( ) is the un-windowed FFT operator. The uniform window is always used. The
FFT( ) and FFTu( ) operators do not calibrate their results since their operands are not
necessarily input time records. To use a calibrated FFT, use the measurement operand
FFT(1) or FFT(2).
IFFT( ) is the inverse complex FFT operation. This operation switches the X axis type.
The Avg( ) operator performs averaging on the operand. The [Average] menu turns
averaging Off/On and selects the Mode, Type and Number of Averages. This operator
allows the explicit use of averaging within a User Function. The measurement operands
(FFT(1) or FFT(2)) are NOT already averaged. Use Avg( ) to perform averaging on
operands or operand terms (e.g. Avg( FFT(1) ) or Avg( FFT(2)/FFT(1) ) ).
The VecAvg( ) operator always performs vector averaging on the operand. Averaging is
performed regardless of the Average Off/On selected in the [Average] menu. The menu
still determines the Average Type and Number of Averages.
d/dx( ) is the derivative operator. The derivative is performed with respect to the X-axis
bin number, not the x-axis values. For example, to convert d/dx( ) to d/df( ) for a linear