5-17.
RF OUTPUT POWER FLATNESS ADJUSTMENT (Cont’d)
Procedure
1. Calculate a correction factor for the HP 8485A Power Sensor as follows:
Find the CAL FACTOR end points (0.05 GHz and the maximum OUT RF Output frequency) by
either using a calculator to find
the best straight line approximation to the CAL FACTOR curve in
percent or by using a straight edge for the best
straight line approximation on the CAL FACTOR
curve located on the body of the power sensor.
Convert both end points to dB using the following equation:
Endpoint (dB)
=
—1 Olog(endpoint(%)/1 00)
Calculate the slope as follows:
HP 8340B:
Slope
(dB/GHz)
[26.5
GHz Endpoint (dB)
—
0.05 GHz Endpoint (dB)]/26.45
HP 8341 B:
Slope (dB/GHz)
=
[20GHz Endpoint (dB)
—
0.05
GHz Endpoint (dB)]/19.95
2. Connect the HP 8485A power sensor to the power meter and then turn the OUT’s and the power
sensor s LINE switches ON. Connect the oscilloscope as shown in Figure
5-61. Allow 30 minutes
for the equipment to warm up.
3. Calibrate and zero the power meter. On the OUT, press [INSTRPRESET] [CW] [4]
[.]
[5] [GHz]
and then
[RF]to turn the RF off. Zero the power meter. To ensure that the power meter is properly
zeroed, select WATT mode, and press the ZERO button until the power meter indicates <0.02 on
the most sensitive range. Select the dBin MODE on the power meter.
4. On the OUT, press [INSTRPRESET] [START][2]
[.] [4]
[GHz].Press [POWERLEVEL] [0] [dBm]
[SWEEPTIME] [5] [sec]. Press [SLOPE],enter the slope calculated in step 1, and terminate the
entry by pressing
[dBm].Save this instrument state by pressing [SAVE][1].
5. Set the oscilloscope to A vs B. Set the horizontal sensitivity (CHAN B) for 1 V/Div and the vertical
sensitivity (CHAN A)
for
0.1 V/Div. Adjust the
oscilloscope’s vertical position control to center the
trace on the oscilloscope. Adjust the horizontal position control to display the entire trace.
6. On the OUT, press [INSTRPRESET] [CW] [1] [4] [GHz] [SHIFT][POWERLEVEL]
[.]
[0] [5]
[dBm][POWER LEVEL]
[-]
[1][dBm].
Press RANGE HOLD on
the power meter and set the CAL
FACTOR % dial
for the 14 GHz CAL
FACTOR indication on
the power sensor.
7. Using the OUT’s front panel rotary knob (RPG),
increase
the power level until the power meter
indicates 0 dBm. The output power sensitivity on the OUT is 0.05 dBin so adjust the power level
for the closest reading to 0 dBin
if you cannot adjust
for exactly 0 dBm.
8. Adjust the oscilloscope’s CHAN A position control to
place
the dot on the center horizontal
graticule. Determine the dB/Oiv sensitivity of the oscilloscope by rotating the OUT’s
rotary knob
until the dot is 1 major graticule above the center graticule. Determine the sensitivity by reading the
power level on the power meter. Repeat this process and determine the sensitivity for the second
major graticule above the center graticule and the two major divisions below the center graticule.
Once the oscilloscope is calibrated in this manner, you can use the oscilloscope’s display to
determine the power flatness of the trace. The scope should now be set up for
2.4 GHz/Div (X-
Axis) and approximately 0.4 dB/Oiv (Y-Axis).
5-116
Adjustments
HP 8340B/41B