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The Spectrum Application (RF Measurements)
R&S
®
FPL1000
382
User Manual 1178.3370.02 ─ 03
7.5.1 Impact of the Vertical Axis Settings
Some background knowledge on the impact of the described settings is provided here
for a better understanding of the required configuration.
7.5.1.1
Reference Level
The reference level value is the maximum value the AD converter can handle without
distortion of the measured value. Signal levels above this value will not be measured
correctly, which is indicated by the "IF Overload" status display.
Internally, the reference level is also used to determine the optimum hardware settings
for the R&S
FPL1000. The defined reference level should correspond with the maxi-
mum expected RF input level.
When determining the expected input level, consider that the power from
all
input sig-
nals contribute to the total power. The reference level must be higher than the total
power from all signals.
The optimum reference level for the current measurement settings can be set automat-
ically by the R&S
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
on page 386), the mea-
surement is restarted.
In general, the R&S
FPL 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 impedance,
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.
Amplitude and Vertical Axis Configuration