Waveform analysis
R&S
®
RTO6
270
User Manual 1801.6687.02 ─ 05
Cut-off frequency for lowpass FIR filter
The cut-off frequency depends on the horizontal resolution and the filter characteris-
tics. The frequency for the lowpass filter can only be set in this range:
f_g_3dB = (0.001 ... 0.2)* f_a_in
for Gaussian FIR filter
f_g_3dB = (0,001 ... 0.4)* f_a_in
for rectangular FIR filter
Where:
f_g_3dB
= cut-off frequency to be set for the lowpass filter, and
f_a_in
= recip-
rocal of the resolution, or sample rate.
Cut-off frequency for highpass FIR filter
To check limit frequency for the highpass filter, convert it to an equivalent lowpass fre-
quency:
f_LP = f_a_in/2 - f_HP
Where f_HP is the requested highpass limit frequency and f_LP the equivalent lowpass
frequency that has to comply with the limits given above.
Bandpass and bandstop FIR filter: CSV file
To define a bandpass or bandstop, you need a CSV file that contains the comma-sepa-
rated filter coefficients. The maximum number of filter coefficients is 2
048
000
taps. No
other parameters are allowed in the file.
To create the CSV file, we recommend using the Matlab Filter Design & Analysis tool.
In the tool, enter the filter type, filter order and filter frequencies. Make sure to set the
sample frequency in Matlab and the sample rate at the oscilloscope to the same value.
If the values differ, the filter is shifted in frequency.
In R&S
RTO6, in the "Math" > "Setup" > "Filter", select the filter "Type" = "User
defined", and load the CSV file.
7.3.5.2
FIR filter in the formula editor
You can type the FIR filter formula directly in the "Equation" tab, or open the formula
editor and use the buttons to create the formula.
Highpass and lowpass FIR filter
The general syntax for highpass and lowpass filters is:
Mathematics
