Changing Axis Units - Tektronix 11801C User Manual

Changing Axis Units

11801C User Manual
Usually, the graticule axis labels are units of time on the horizontal axis and
units of voltage on the vertical axis. For some tasks these axis labels are
more meaningful if expressed in other units. Horizontal units of distance are
appropriate for TDR and TDT measurements. The 11801C allows you to
specify the horizontal axis units to be feet, meters or inches. You can also
specify the propagation delay, which is the fraction of the speed of light at
which signals travel through your transmission line.
The vertical axis units most appropriate to TDR measurements are either
units of rho (r) or of impedance (Z). The 11801C lets you specify units of rho
for the vertical axis. Rho values can be converted to impedance values by
using the following equation (where Z0 is usually 50 W):
1 + r
Z = Z0
1 r
Changing axis units on one graticule also changes the axis units of
all graticules displayed.
However, readout of impedance is available from the Cursors menu whenev
er the vertical axis is scaled in rho units.
The status area of the Graticules selector in the Waveform major menu
always shows the number of graticules and the axis units of measure.
Rho is not selectable for vertical axis units unless the selected trace is dis
played in Volts units and TDR is turned on.
Vertical Axis Units
To change the vertical axis units, use the Graticules pop up menu in the
Waveform major menu. The section of this pop up menu labeled Y Units
governs the vertical axis units.
You can touch either the Volts or Rho selectors to set the vertical axis labels
to those units. The current setting is highlighted.
Rho is not selectable unless the following are true:
H The selected trace can be displayed in Volts units, as opposed to U or N
units. Traces such as Log (M1)" or M1/M2" are not scaled in Volts and
therefore cannot be scaled in Rho. Any linear combination of channels
and stored traces can be displayed in Volts or Rho.
H TDR must be on in all channels in the selected trace.
NOTE
Graticules
3 87