Concepts and features
R&S
®
ZNB/ZNBT
204
User Manual 1173.9163.02 ─ 62
In practice, the frequency-dependent part ist often dominant, so that
Loss
DC
can be set
to zero. Experimentally, the loss value at DC can be determined in a separate mea-
surement at a very low frequency (f --> 0).
4.6.1.3
Auto Length
The "Auto Length" function adds an electrical length offset to the active trace's receive
port, such that the residual delay of the active trace (defined as the negative derivative
of the phase response) is minimized across a configurable frequency range. If "Delay"
is the selected trace format, the entire trace is shifted in vertical direction and centered
on zero. In phase format, the "Auto Length" corrected trace shows the deviation from
linear phase.
Length and delay measurement, related settings
"Auto Length" is suited for length and delay measurements on transmission lines.
1. Connect a (non-dispersive) cable to a single analyzer port no. n and measure the
reflection factor S
nn
.
2. In the Channel – [Offset
Embed] > "Offset" softtool tab, select "Auto Length".
The delay is displayed in the "Delay" field, the cable length (depending on the
"Velocity Factor") in the "Mech. Length" field.
It is also possible to determine cable lengths using a transmission measurement. Note
that "Auto Length" always provides the
single
cable length and the delay for propaga-
tion in
one
direction.
The analyzer provides alternative ways for delay measurements:
1. Measure the reflection factor and select Trace – [Format] > "Delay".
This yields the delay for propagation in forward and reverse direction and should
be approx. twice the "Auto Length" result. For transmission measurements, both
results should be approx. equal.
2. Measure the reflection factor and select Trace – [Format] > "Phase". Place a
marker to the trace and activate Trace – [Trace
Config] > "Trace Statistics" >
"Phase/El Length".
This yields the delay in one direction and should be approx. equal to the "Auto
Length" result.
The measurement results using trace formats and trace statistics functions depend on
the selected delay aperture and evaluation range. "Auto Length" is particularly accu-
rate because it uses all sweep points. For non-dispersive cables, aperture and evalua-
tion range effects are expected to vanish.
Offset parameters and de-/embedding
