Keysight EXG and MXG X-Series Signal Generators User’s Guide 115
Optimizing Performance for All Models
Using External Leveling (N5173B/83B Only)
Figure 5-19 ALC Circuity
The external detector outputs a negative voltage to the signal generator’s rear panel ALC INPUT
connector based on the power level at the detector. As the RF power level at the coupler’s/power
splitter input changes, the external detector returns a compensating negative voltage. The ALC
circuit uses this negative voltage to level the RF output power by raising and lowering the signal’s
power, thus ensuring a constant power level at the point of detection (external detector). Since the
point of detection does not occur at the output of the device to which the detector is connected,
there is some power loss that is not compensated for by the external detector. For example on a
coupler, the coupled port siphons some of the signal’s energy to drive the external detector. In
addition the coupler experiences some insertion loss between the coupled port and the output.
Figure 5-21 on page 116 shows the input power versus output voltage characteristics for typical
Keysight Technologies diode detectors. Using this chart, you can determine the leveled power at
the diode detector input by measuring the external detector output voltage. For a coupler, you
must then add the coupling factor to determine the leveled output power.
When using an external detector, the signal generator’s power range may vary from the values
shown in the data sheet. This is primarily due to the efficiency of the detector. Always ensure that
the detector, coupler/power splitter are specified for the power and frequency range of interest. To
determine the signal generator’s actual power range during external leveling, see “Determining the
Signal Generator’s Amplitude Range” on page 119.
With external leveling, the displayed amplitude value can vary significantly from the actual output
power of the coupler/power splitter to which the external detector is connected (see Figure 5-20).
This is because the coupler/power splitter has it own signal characteristics (insertion loss, coupling
factor, and so forth), which are unknown to the signal generator, so it is typically unable to display
an accurate amplitude value. Also components between the signal generator and the external
detector can affect the output power of the coupler/power splitter. You can compensate for this
power display difference by using the
Ext Leveling Amptd Offset softkey or the Amptd Offset softkey. The difference between the two
softkeys is that the Ext Leveling Amptd Offset functions only while external leveling is active. For
more information on using the external leveling offset feature, see “Adjusting the Signal Generator
Display’s Amplitude Value” on page 120.
External Detector
Power Splitter
Component
DUT
RF
Cabling
OUTPUT
ALC INPUT
ALC Modulator
ALC
Internal Detector
Driver
Signal Generator
Leveled Output
(Amp, Filter,
Atten, etc.)
(Negative output)
or Coupler
Opt 1E1 Output
Attenuator
To Next Page
Loading...
Need help?
General
