Giga-tronics 2508A, Operation Manual

Page: 60 / 132

Chapter 2: Front Panel Operation
60 2500A Series Operation Manual, 34172 Revision C, March 2008
6. Perform the following loss compensation actions, as desired (both features can be used concur-
rently):
• To compensate for a fixed level of loss , select the “Power Offset” menu item, and enter the
desired loss correction using either the numeric keypad, Step Up/Step Down buttons, or the rotary
knob. Note that when a correction factor is entered,
OFS appears in the upper right corner of the
display.
• To compensate for a loss that varies linearly with frequency , select the “Power Slope” menu
item, and enter the desired correction factor using either the numeric keypad, Step Up/Step Down
buttons, or the rotary knob. Note that when this correction factor is entered,
SLP appears in the
upper right corner of the display.
7. To adjust the phase of the output, select the "Phase Adjust" menu item, and enter the desired phase
shift using either the numeric keypad, Step Up/Step Down buttons, or the rotary knob.
NOTE:
Whenever the frequency of the instrument is changed, the Phase Adjust setting will reset to 0
degrees. The Phase Adjust range is 500 MHz to the maximum frequency of the instrument.
Phase adjust is available for frequencies below 500 MHz; however, the output response time
is increased.
8. If the LED indicator that is above the RF ON button is not lit, press the RF ON button to enable the
signal at the RF output connector.
9. Verify that the Unleveled indicator is not lit.
If the Unleveled indicator is lit, then the combination of output power level, power offset, power
slope, and step attenuator mode (if applicable) is set inappropriately, and the RF output is unleveled.
Adjust the combination of settings until the Unleveled indicator turns off.
2.4.3.2 Generating an External ALC Leveled Signal
The following procedure describes how to set up the instrument to generate an externally level controlled
signal using the External ALC feature. This procedure can be used in CW, Ramp, and Pulse modes only.
The output of the instrument is typically sampled through a directional coupler or power splitter. The sig-
nal is sampled using a positive or negative crystal detector or power meter. External ALC response with
the instrument configured for Pulse Modulation varies according to duty cycle of the signal being sam-
pled. 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 out-
put, it may be necessary to characterize the output of the crystal detector output to a power standard. The
external positive or negative crystal detector ALC procedure follows:
1. Connect the input of the crystal detector to the sample port of the power splitter or directional cou-
pler.