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Model 8902A
Operation
Tuned RF Level
FUNCTIONS
Synchronoiis and Average TUNED RF LEVEL, CALIBRATE, SET REF, Special Functions 38 and
39 (Display and Enter Tuned R F Level Calibration Factors), Special Function
4
(Tuned RF Level
Selection and Display Averaging)
DESCRIPTION
The Measuring Receiver can accurately measure the absolute or relative level of extremely low-
level, continuous wave (CW), R F signals. At each measurement frequency, the instrument must
be calibrated to correct for frequency-dependent measurement variations. Calibration over the full
dynamic range requires calibration at three different levels. The calibration remains valid for any
CW signal at that frequency
f5%
(or
&IO
MHz, whichever is smaller).
Requirements for the Tuned
RF
Level Measurement
Before an absolute Tuned R F Level measurement can be made, the following 3 requirements must
be met. Before a relative Tuned RF Level measurement can be made, only requirements 2 and 3
must be met (since no power sensor is used during relative measurements):
1. The R F Power measurement must be calibrated.
The accuracy of the Tuned RF Level measurement depends o n a calibrated RF Power
measurement made with an external power sensor. (RF Power calibration is discussed in
detail in R F Power on page 3-75.)
2. The Measuring Receiver must be properly tuned.
The Measuring Receiver can be tuned manually or automatically. When manually tuning,
enter a frequency value into the Measuring Receiver within
f2.5
kHz for frequencies
12.5
MHz. within k 2 kHz for frequencies between 2.5 MHz and 10 MHz, and within
f50
kHz for frequencies
2
10
MHz. When automatically tuning, select FREQ and ensure
that the initial input signal level is greater than -20 dBm. (RF Freqircncy Tuning on page
3-141 has more details on the different types of tuning available.)
3. The Tuned R F Level calibration factors for the frequency being measured must be in place.
To calibrate the Tuned RF Level measurement (and allow the Measuring Receiver to
create calibration factors), step the input signal down and select the CALIBRATE key
(while keeping the signal level constant) each time RECAL is displayed. Each time the
CALIBRATE key is pressed, the Measuring Receiver creates a calibration factor from a
comparison of the two measured levels.
Up to three calibration factors will be created. These three Tuned RF Level calibration
factors remain valid regardless of power level as long as the signal frequency is the same.
Each individual calibration factor is tagged with the frequency at which it is valid, and
the status of the first three filters in the front of the instrument (Special Function 3 and
Special Functions 1.0 and 1.9).
If
any of these conditions change, the calibration factor
becomes invalid.
The Tuned RF Level measurement must be recalibrated if the frequency is changed.
Tuned R F Level calibration can be performed during the actual measurement. Tuned
R F Level calibration factors can be entered (using the Store/Recall function or Special
Functions 38 and 39) if you have measured that frequency before.
rcv. I h1.4 Y86
3-95
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