Solving Problems
If You Encounter a Problem
Chapter 480
Signal Loss Occurs While Working with Spectrum Analyzers
The effects of reverse power, when using the signal generator with a spectrum analyzer that
does not have preselection capability, can cause problems with the signal generator’s RF
output.
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 (typically 10 kHz CW and 100 kHz for modulated signals), 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
mode or power search mode.
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.
To set the signal generator to the ALC off mode, follow these steps:
1. Press
Preset.
2. Press
Frequency, enter the required frequency, and terminate the entry with the
appropriate terminator softkey.
3. Press
Amplitude, enter the required amplitude, and terminate the entry with the
appropriate terminator softkey.
4. Press
RF On/Off.
5. Press
Amplitude > ALC Off On.
This deactivates the signal generator’s automatic leveling control.
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.
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