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The EXT indicator is activated in the AMPLITUDE area of the display. NOTE For signal generators with Option 1E1, notice that the ATTN HOLD (attenuator hold) annunciator is displayed. During external leveling, the signal generator automatically uncouples the attenuator from the ALC system for all external leveling points. While in this mode, the RF output amplitude adjustment is limited to -20 to +25 dBm, the adjustment range of the ALC circuitry. For more information, see “External Leveling with Option 1E1 Signal Generators” on page 133. 6. Observe the coupling factor printed on the directional coupler at the detector port. Typically, this value is -10 to -20 dB. Enter the positive dB value of this coupling factor into the signal generator. 7. Press More (1 of 2) > Ext Detector Coupling Factor > 16 (or the positive representation of the value listed at the detector port of the directional coupler) > dB. Leveled output power is now available at the output of the directional coupler. NOTE While operating in external leveling mode, the signal generator’s displayed RF output amplitude is affected by the coupling factor value, resulting in a calculated approximation of the actual RF output amplitude. To determine the actual RF output amplitude at the point of detection, measure the voltage at the external detector output and refer to Figure 4-3 or measure the power directly with a power meter. Determining the Leveled Output Power Figure 4- 3 shows the input power versus output voltage characteristics for typical Agilent Chapter 4 131 Optimizing Performance Using External Leveling Technologies diode detectors. Using this chart, you can determine the leveled power at the diode detector input by measuring the external detector output voltage. You must then add the coupling factor to determine the leveled output power. The range of power adjustment is approximately -20 to +25 dBm. Figure 4-3 Typical Diode Detector Response at 25° C 132 Chapter 4 Optimizing Performance Creating and Applying User Flatness Correction External Leveling with Option 1E1 Signal Generators Signal generators with Option 1E1 contain a step attenuator prior to the RF output connector. During external leveling, the signal generator automatically holds the present attenuator setting (to avoid power transients that may occur during attenuator switching) as the RF amplitude is changed. A balance must be maintained between the amount of attenuation and the optimum ALC level to achieve the required RF output amplitude. For optimum accuracy and minimum noise, the ALC level should be greater than -10 dBm. For example, leveling the CW output of a 30 dB gain amplifier to a level of -10 dBm requires the output of the signal generator to be approximately -40 dBm when leveled. This is beyond the amplitude limits of the ALC modulator alone, resulting in an unleveled RF output. Inserting 45 dB of attenuation results in an ALC level of +5 dBm, well within the range of the ALC modulator. NOTE In the example above, 55 dB is the preferred attenuation choice, resulting in an ALC level of +15 dBm. This provides adequate dynamic range for AM or other functions that vary the RF output amplitude. To achieve the optimum ALC level at the signal generator RF output of -40 dBm for an unmodulated carrier, follow these steps: 1. Press Amplitude > Set Atten > 45 > dB. 2. Press Set ALC Level > 5 > dBm. This sets the attenuator to 45 dB and the ALC level to +5 dBm, resulting in an RF output amplitude of -40 dBm, as shown in the AMPLITUDE area of the display. To obtain flatness-corrected power, refer to “Creating and Applying User Flatness Correction” on page 133. To Level with a mm-Wave Source Module Millimeter-wave source module leveling is similar to external detector leveling. The power level feedback signal to the ALC circuitry is taken from the millimeter-wave source module, rather than the internal signal generator detector. This feedback signal levels the RF output power at the mm-wave source module output through the signal generator’s rear panel SOURCE MODULE interface connector. For instructions and setups, see Chapter 12, “ Peripheral Devices,” on page 239. Creating and Applying User Flatness Correction User flatness correction allows the digital adjustment of RF output amplitude for up to 1601 frequency points in any frequency or sweep mode. Using an Agilent E4416A/17A or E4418B/19B power meter (controlled by the signal generator through GPIB) to calibrate the measurement system, a table of power level corrections is created for frequencies where power level variations or losses occur. These frequencies may be defined in sequential linear steps or arbitrarily spaced. To allow different correction arrays for different test setups or different frequency ranges, you may save individual user flatness correction tables to the signal generator’s memory catalog and recall them on demand. Use the steps in the next sections to create and...

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