Operation
Manual 20791, Rev. C, June 2001
2-103
softkey. Turn averaging ON by pressing the [
AVGON/OFF
] softkey. Use the spin knob or numeric
entry keypad to select the desired number of averages. To restart the averaging, turn the averaging OFF
then ON again.
2.13.2.2
Swept Mode with AC Detection
If you are making swept measurements, ac detection mode will tend to give you better low level
measurements than dc detection. The reason is that in ac detection mode, the sweeper output is
chopped, and the analyzer constantly compares the RF ON level to the RF OFF level. Because the
analyzer is always measuring the RF OFF level, the effects of drift are effectively canceled. The
disadvantage of the swept-ac mode compared to the CW mode is that it takes much longer to average to
a stable reading since only one average is made per sweep.
To use ac detection, first make sure that you are in the swept measurement mode. Press
[MEAS]
and
select the [
ALL SWEPT
] softkey, or press
[DEFINE]
and select the [
CW/SWEPT
] softkey. Select ac
detection by pressing
[CONFIG]
and selecting the [
SENSORSAC/DC
] softkey. Then, either press the
[
ALLAC
] softkey or the [
SENSRXAC/DC
] softkey - where X is the desired sensor letter. This will put
the analyzer in the ac detection mode. Make sure that the AC MOD OUTPUT BNC connector on the
8003 Analyzer’s rear panel is connected to the sweeper PULSE MOD or AM input (see Section B.3.3.1
for the sweeper configuration instructions). If the sweeper is not GPIB supported, make sure that it’s
AM or PULSE modulation function is also enabled.
To make the best measurements in swept-ac detection mode, first zero the sensor using the method
described in the CW mode in Section 2.13.2.1. Although frequent re-zeroing is not required since the
ac detection is eliminating drift, an initial zero is required for accurate absolute power displays. Use a
slow sweep (1 second) to ensure adequate resolution. Turn on averaging to reduce signal noise. To use
averaging, first press
[DISPLAY]
and select the [
AVG
] softkey. Turn averaging on by pressing the
[
AVG ON/OFF
] softkey. Then select the appropriate averaging number using the spin knob or numeric
entry keypad. To restart the averaging, turn the averaging OFF then ON again.
2.13.2.3
Swept Mode with DC Detection
There may be occasions when swept low level measurements cannot be made in ac detection mode. An
example may be testing an amplifier with an AGC control that cannot handle ac modulation. In these
cases, the dc detection mode can be used. However, it may be difficult to adequately average out noise
quickly enough to avoid the effects of drift. This will typically be the case for measurements below
-60 dBm. To use dc detection, first make sure that the analyzer is in swept mode using the instructions
for ac detection given previously. Then press
[CONFIG]
and select the [
SENSORS AC/DC
] softkey.
Either press the [
ALL DC
] softkey, or toggle the desired [
SENSRXAC/DC
] softkey until DC is in light
blue. Note that dc detection is the default mode of the analyzer.
To make the best swept low level measurements in dc detection mode you should first make sure that
the analyzer has reached a very stable operating temperature to minimize the drift. Then, frequently re-
zero the analyzer using the instructions given in the CW Mode in Section 2.13.2.1. Turn on averaging
to reduce signal noise using the instructions given in the Swept Mode With AC Detection in
Section 2.13.2.2.
Содержание 8003
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