Concepts and Features
R&S
®
ZNC
93
User Manual 1173.9557.02 ─ 13
Loss" tab. For a lossless transmission line, Loss
DC
= Loss(f
ref
) = 0 dB. In practice, the
frequency-dependent loss often represents the dominant contribution so that Loss
DC
can
be set to zero.
Experimentally, the two loss values Loss
DC
and Loss(f
ref
) are determined in two separate
measurements at a very low frequency (f --> 0) and at f = f
ref
.
3.6.1.3
Auto Length
The "Auto Length" function ("CHANNEL > OFFSET EMBED > Offset > Auto Length")
adds an electrical length offset to a test port with the condition that the residual delay of
the active trace (defined as the negative derivative of the phase response) is minimized
across the entire sweep range. If "Delay" is the selected trace format, the entire trace is
shifted in vertical direction and centered around 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. Select "Auto Length".
The delay is displayed in the "CHANNEL > OFFSET EMBED > Offset > Auto
Length" tab. The cable length, depending on the velocity factor, can be read in the
"Mechanical 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 a 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 accurate
because it uses all sweep points. For non-dispersive cables, aperture and evaluation
range effects are expected to vanish.
Use "Zero Delay at Marker" to set the delay at a special trace point to zero.
Offset Parameters and Embedding