Concepts and Features
R&S
®
ZNB/ZNBT
197
User Manual 1173.9163.02 ─ 38
The harmonic grids can not be calculated for any set of sweep points. If the minimum
number of sweep points is smaller than 5, then the interpolation/extrapolation algorithm
for additional sweep points will not work. The same is true if the number of sweep
points or stop frequency exceeds the upper limit. Besides, the ratio between the sweep
range and the interpolation range between f = 0 and f = f
min
must be large enough to
ensure accurate results. If the sweep range for the harmonic grid exceeds the fre-
quency range of the current system error correction, a warning is displayed.
Finding the appropriate algorithm
The three types of harmonic grids have different advantages and drawbacks. Note that
for a bandpass transformation the grid parameters have the following effect:
●
A wider sweep range (i.e. a larger bandwidth) increases the time domain resolu-
tion.
●
A smaller frequency gap extends the unambiguous range.
●
A larger number of points increases the sweep time.
With default analyzer settings, the difference between the grid types are small. The fol-
lowing table helps you find the appropriate grid.
Table 4-19: Properties of grid types
Grid type: Keep
Sweep
time
Time
domain
resolution
Unambig-
uous
range
Algorithm fails if...
Stop freq. and no. of
points
–
Freq. gap and no. of
points
Stop frequency beyond upper fre-
quency limit
Stop freq. and approx.
freq. gap
Number of sweep points beyond limit
4.7.2.5
Time Gates
A time gate is used to eliminate unwanted responses that appear on the time domain
transform. An active time gate acts on the trace in time domain as well as in frequency
domain representation.
The properties of the time gates are analogous to the properties of the frequency
domain windows. The following table gives an overview:
Table 4-20: Properties of time gates
Window
Sidelobe
suppression
Passband
ripple
Best for...
Steepest Edges
(Rectangle)
13 dB
0.547 dB
Eliminate small distortions in the vicinity of the
useful signal, if demands on amplitude accu-
racy are low
Steep Edges
(Hamming)
43 dB
0.019 dB
Good compromise between edge steepness
and sidelobe suppression
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