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Two-port measurements with the tracking generator
R&S FSH
1145.5973.12 4.94
E-14
Measuring the group delay when measuring transmission
The R&S FSH can calculate the GROUP DELAY from the phase difference and frequency difference
(aperture) of two test points and display it over the frequency. The group delay is defined as the
negative derivation of the phase
Z
over the angular velocity . This yields
g
= -(d
/ 360
o
df) for the
group delay, where d
is the change in phase in degrees within the frequency increment df (df is also
designated as aperture). The aperture most favorable for a concrete measurement task must be set on
a case-by-case basis by using the phase characteristic, where the fastest speed of phase shift in the
frequency range in question is the deciding factor. If the value is too large, details will be lost; if it is too
small, the influence of result-value noise will be too great.
Press the MEAS MODE softkey.
Using the rotary knob or the cursor keys, select
GROUP DELAY from the menu and confirm by
pressing either the MEAS MODE softkey or the
ENTER key.
A field for entering the aperture will open and indicate
the aperture value currently selected. The default
setting is an aperture width of ten
test points.
Acceptable entry values are whole numbers from 1 to
300. For example, an entry of APERTURE
= 5 tells the
system to use the phase values of test points n-3 and
n+2 when performing the calculation at test point n.
You can enter a suitable aperture value by using
the numeric keys. To confirm, press the ENTER
key or one of the units keys.
Alternatively, you can adjust the aperture value
using the rotary knob or cursor keys and confirm
with the ENTER key.
The R&S FSH will now show the group delay trace.
The upper right-hand corner of the display will indicate
Group Delay transm. .
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