Ronde & Schwarz 1304.0004K03, Руководство пользователя

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The Spectrum Application (RF Measurements)
R&S
®
FPL1000
311 User Manual 1178.3370.02 ─ 11
The optimum reference level for the current measurement settings can be set automat-
ically by the R&S
FPL1000 (see "Reference Level" on page 313).
The reference level determines the amplitude represented by the topmost grid line in
the display. When you change the reference level, the measurement is not restarted;
the results are merely shifted in the display. Only if the reference level changes due to
a coupled RF attenuation (see
"Attenuation Mode / Value" on page 315), the measure-
ment is restarted.
In general, the R&S FPL1000 measures the signal voltage at the RF input. The level
display is calibrated in RMS values of an unmodulated sine wave signal. In the default
state, the level is displayed at a power of 1 mW (= dBm). Via the known input impe-
dance, conversion to other units is possible.
Reference level offset
If the signal is attenuated or amplified before it is fed into the R&S FPL1000, you can
define an (arithmetic) offset to the reference level so the application shows correct
power results. All displayed power level results are shifted by this value, and the scal-
ing of the y-axis is changed accordingly.
To determine the required offset, consider the external attenuation or gain applied to
the input signal. For attenuation, define a positive offset so the R&S
FPL1000 increa-
ses the displayed power values.
If an external gain is applied, define a negative offset so the R&S FPL1000 decreases
the displayed power values.
Note, however, that the internal reference level (used to adjust the hardware settings to
the expected signal optimally) ignores any "Reference Level Offset". Thus, it is impor-
tant to keep in mind the actual power level the R&S
FPL1000 must handle, and not to
rely on the displayed reference level.
internal reference level = displayed reference level - offset
Example
1. The initial reference level is 2 dBm with no offset.
Both the displayed reference level and the internal reference level are 2 dBm.
2. An offset of 3 dB is defined.
The displayed reference level is adjusted to 5 dBm.
The internal reference level remains at 2 dBm.
(5 dBm (displayed ref level) - 3 dB (offset) = 2 dBm)
3. Now the user decreases the reference level to 1 dBm.
The displayed reference level is adjusted to 1 dBm.
The internal reference level is adjusted to:
1
dBm (displayed ref level) - 3 dB (offset) = -2 dBm.
Amplitude and Vertical Axis Configuration