Filter
Top Products
192 Chapter 10
Troubleshooting
RF Output Power Problems
Signal Loss While Working with a Spectrum Analyzer
The effects of reverse power can cause problems with the signal generator’s RF output when the signal
generator is used with a spectrum analyzer that does not have preselection capability.
Some spectrum analyzers have as much as +5 dBm LO feedthrough at their RF input port at some
frequencies. If the frequency difference between the LO feedthrough and the RF carrier is less than the ALC
bandwidth, the LO’s reverse power can cause amplitude modulation of the signal generator’s RF output. The
rate of the undesired AM equals the difference in frequency between the spectrum analyzer’s LO
feedthrough and the RF carrier of the signal generator.
Reverse power problems can be solved by using one of two unleveled operating modes: ALC off or power
search.
Setting ALC Off Mode
ALC off mode deactivates the automatic leveling circuitry prior to the signal generator’s RF output. In this
mode, a power meter is required to measure the output of the signal generator and assist in achieving the
required output power at the point of detection.
Use the following steps to set the signal generator to the ALC off mode:
1. Preset the signal generator: press
Preset.
2. Set the desired frequency: press
Frequency and enter the desired frequency.
3. Set the desired amplitude: press
Amplitude and enter the desired amplitude.
4. Turn the RF off: set
RF On/Off to Off
5. Turn the signal generator’s automatic leveling control (ALC) off: press
Amplitude > ALC Off On to Off.
6. Monitor the RF output amplitude as measured by the power meter.
7. Press
Amplitude and adjust the signal generator’s RF output amplitude until the desired power is
measured by the power meter.
Setting Power Search Mode
Power search mode executes a power search routine that temporarily activates the ALC, calibrates the power
of the current RF output, and then disconnects the ALC circuitry.
Use the following steps to set the signal generator to manual fixed power search mode:
1. Preset the signal generator: press
Preset.
2. Set the desired frequency: press
Frequency and enter the desired frequency.
3. Set the desired amplitude: press
Amplitude and enter the desired amplitude.
4. Turn the signal generator’s automatic leveling control (ALC) off: press
Amplitude > ALC Off On to Off.
5. Turn the RF on: set
RF On/Off to On.
6. Press
Do Power Search.
This executes the manual fixed power search routine, which is the default mode.