The Spectrum Application (RF Measurements)
R&S
®
FPL1000
309
User Manual 1178.3370.02 ─ 09
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.
7.5.1.2
RF Attenuation
The attenuation is meant to protect the input mixer from high RF input levels. The level
at the input mixer is determined by the set RF attenuation according to the formula:
"level
mixer
= level
input
– RF attenuation"
The maximum mixer level allowed is -13 dBm.
Mixer levels above this value may lead to incorrect measurement results, which is indi-
cated by the "RF Overload" status display. Furthermore, higher input levels may dam-
age the instrument. Therefore, the required RF attenuation is determined automatically
according to the reference level by default.
High attenuation levels also avoid intermodulation. On the other hand, attenuation
must be compensated for by re-amplifying the signal levels after the mixer. Thus, high
Amplitude and Vertical Axis Configuration
