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Agilent E8663B Analog Signal Generator User’s Guide
Optimizing Performance
Using External Leveling
sampling the fast rising edges of pulsed waveforms with high crest factors found in formats such as
802.11b, CDMA, and OFDM. A limited, or narrow bandwidth will result in a longer ALC sample time
and a more accurate representation of the signal’s level.
Using External Leveling
The signal generator can be externally leveled by connecting an external sensor at the point where
leveled RF output power is desired. This sensor detects changes in RF output power and returns a
compensating voltage to the signal generator’s ALC input. The ALC circuitry raises or lowers (levels)
the RF output power based on the voltage received from the external sensor, ensuring constant power
at the point of detection.
To Level with Detectors and Couplers/Splitters
External Leveling the Signal Generator
The signal generator contains 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.
illustrates a typical external leveling setup. The power level feedback to the ALC circuitry
is taken from the external negative detector, rather than the internal signal generator detector. This
feedback voltage controls the ALC system, leveling the RF output power at the point of detection.
To use detectors and couplers/splitters for external leveling at an RF output frequency of
10 GHz and an amplitude of 0 dBm, follow the instructions in this section.
Required Equipment
•
Agilent 8474E negative detector
•
Agilent 87301D directional coupler
•
cables and adapters, as required
Connect the Equipment
Set up the equipment as shown in
.
