HP 8340b Operating Instructions

UNLEVELED
RF
Figure 3-29. ALC Loop Block Diagram
POWER dBm Display
If the requested power is greater than can be provided, the level control loop will provide maximum
available power and light the UNLEVELED annunciator. When unleveled, the output power does not
equal the value shown in the ENTRY DISPLAY. The internal detector is monitoring the actual power,
however, and its output voltage controls the POWER dBm display. The detector voltage is interpreted
to give ALC level, and the attenuator setting is subtracted to yield actual output power, even when
unleveled.
The AM input is DC coupled, and a DC input will change the output power. This change does not
appear in the ENTRY DISPLAY, but the POWER dBm display accurately indicates the real output.
When the instrument is internally leveled, the UNLEVELED annunciator is off, and AM is off, the
POWER dBm display simply repeats the value shown in the ENTRY DISPLAY. When externally lev¬
eled, or the UNLEVELED annunciator is on, or AM is on, the POWER dBm display indicates the ALC
level and reflects the true output power. This might not agree with the ENTRY DISPLAY value, which
shows the desired level in the absence of modulation.
HP 8340B/41B
Operating Information
3-99

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English