User`s guide

130 Chapter 4
Performance Tests
5. 3 dB Bandwidth
Performance Tests
5. 3 dB Bandwidth
Description
The preselector peak digital-to-analog converter (DAC) is used to tune the center
frequency of the preselector filter until the input signal is 3 dB down on the skirts of the
filter. The 3 dB bandwidth is calculated from the DAC values.
Procedure
1. Connect an SMA cable from the 1ST LO OUTPUT of the spectrum analyzer to the
INPUT of the 11975A Amplifier. Connect a second SMA cable to the OUTPUT of the
amplifier.
2. Connect the 8481A Power Sensor to the power-meter sensor cable, then zero and
calibrate the 436A Power Meter.
3. Set the spectrum analyzer controls as follows:
SHIFT ⇑ ⇑ ⇑ ⇑ (selects U Band)
FREQUENCY SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz
CENTER FREQUENCY (sets the LO frequency to 5.0 GHz) . . . . . . 50.3 GHz
CAUTION When you are using an 11975A Amplifier with an 11974, you must set the
amplifier rear-panel ALC switch to ON before you connect the amplifier to the
test setup. If the ALC switch is left in the OFF position, the amplifier output
power is high enough to destroy the mixer diodes.
4. On the 11975A Amplifier, set the rear-panel ALC switch to ON, then connect the 8481A
Power Sensor to the free end of the cable installed on the OUTPUT connector of the
amplifier. Set the 436A Power Meter Cal Factor % to the appropriate value for a
frequency of 5 GHz.
5. Adjust the amplifier OUTPUT POWER LEVEL for a reading of +15.2 dBm
±0.1 dBm on
the power meter.
6. Connect the equipment as shown in Figure 4-1 on page 106.
CAUTION Turn off the ac power on the 8349B Amplifier prior to connecting or
disconnecting the source module interface cable.
Turn off the ac power on the 11974-60028 Preselector Power Supply prior to
connecting or disconnecting it from the 11974.
On the 11974 rear panel, set the instrument select switches to the
appropriate settings before applying power to the 11974.