Rohde & Schwarz RTE Series - Page 308

Waveform analysis
R&S
®
RTE
308User Manual 1326.1032.02 ─ 20
Math expression Description
Step2FreqRespNormMag(x,points)
Where:
●
x is the waveform (channel, math, reference)
●
points is the number of points in the resulting
math waveform (min. 1000 points)
Normalized magnitude of transfer function in fre-
quency domain
Example:
Step2FreqRespNormMag(Ch1,2000)
Step2FreqRespNormPhi(x,points,time offset)
Where:
●
x is the waveform (channel, math, reference)
●
points is the number of points in the resulting
math waveform (min. 1000 points)
●
time offset in s
Normalized phase of transfer function in frequency
domain
Example:
Step2FreqRespNormPhi(Ch1,2000,2e-9)
The calculation of transfer functions has several steps:
●
Calculate the frequency domain representation of a step-like signal. A detailed
description is given in: A. M. Nicolson, „Forming the fast Fourier Transform of a
step response in Time-Domain Metrology,“ in Electronic letters, Bd. 9, Nr. 14, p.
317, 1973.
●
Calculate the derivative to convert the result to the transfer function.
●
Normalize the result at DC to a magnitude of 1 V and subtract specified time offset
from phase.
The step-like signal to be analyzed is a time domain waveform, and the result is a math
waveform in the frequency domain.
To get useful results, check and adjust the following settings:
1. Place the analyzed step of the signal in the left half of the time domain diagram.
Use the "Reference point" or the horizontal "Position" of the trigger to move the sig-
nal.
See also: Chapter 5.2, "Horizontal settings", on page 176.
2. Adjust the record lengths of the source signal and the math signal. The "Record
length" of the step-like source signal must be shorter than the number of points in
the resulting math function, which is set in the formula. See also: "Record length"
on page 178.
3. If the resulting math waveform is noisy, increase the "Average count" for the source
signal until the waveform is clear.
See also: Chapter 5.2.2, "Acquisition", on page 181.
The resulting math waveforms are specific FFT waveforms, thus only chosen FFT set-
tings in the "Math" dialog are supported:
●
"Setup" tab:
– "Arithmetic Mode" = Off
– "Vertical Scale"
●
"FFT Gating" tab: all settings
●
"FFT Y-Units" tab:
– "Magnitude unit": recommended units are dBV and Linear
Mathematics