Giga-tronics 2500B Series Microwave Signal Generators
Special Modes
Operation Manual, Part Number 34737, Rev C, June 30, 2011
Page 71
6.2
Use External ALC
One application of this procedure would be a test setup where cables and fixtures connecting to the DUT incur
significant losses, and you want to deliver a precise, known power level to the DUT under dynamic conditions.
With External Automatic Level Control (ALC), the power level close to the DUT is sampled by a power meter or crystal
detector, and the sample is used to generate a signal that is connected to the 2500B. This signal is used to automatically
adjust the RF output power of the 2500B to compensate for the power lost in the cables and fixture. See Figure 36
below.
NOTE:
The example procedures in this section use specific parameters to illustrate how to setup the 2500B. You can use
this procedure for real-life situations by simply changing the parameters to fit your needs.
This section describes two methods for using External ALC:
Use External ALC with a crystal (diode) detector
Use External ALC with a Power meter
Figure 36: Setup for External ALC
Note the following about using external ALC:
ALC can be used in CW, Ramp, and Pulse modes only.
The output of the 2500B is typically sampled through a directional coupler or power splitter. The signal is detected
using a positive or negative crystal (diode) detector or power meter.
External ALC response with the instrument configured for Pulse Modulation varies according to duty cycle of the
signal being sampled. Low duty cycles result in a slower response time for the instrument to level.
Level control for External ALC operation using crystal detectors are described in dBV units.
The crystal detector output may vary for power and frequency. Because of the variability of the crystal detector
output, it may be necessary to characterize the crystal detector output with a power reference standard.
