R&S FSH
Setting the Amplitude Parameters
1145.5973.12 4.7
E-11
Setting the Amplitude Parameters
All R&S FSH settings referred to the level display are made with the AMPT key.
The reference level (REF) is the level represented by the uppermost grid line in the measurement
diagram. The input signal gain up to the display stage is set with the reference level. If the reference
level is low, the gain is high, which means that even weak signals are clearly displayed. If the input
signals are strong, a high reference level must be set to prevent the analyzer signal path from being
overdriven and to keep the signal display within the display range. When displaying the spectrum of a
composite signal, the reference level should be at least high enough to ensure that all the signals are
within the measurement diagram.
The RF attenuation setting at the input of the R&S FSH is directly coupled to the reference level. If the
reference level is high, RF attenuation is switched on in steps of 10 dB according to the following table
so that the input mixer always remains in the linear range.
The R&S FSH has two different modes for the attenuation setting. The modes are selected using the
SETUP key and the GENERAL softkey (see chapter 1). In Low Distortion mode, the R&S FSH sets the
RF attenuation 10 dB higher in line with the table, making the stress of the input mixer 10 dB less at the
specified reference level. If the spectrum is densely occupied with signals, as occurs in a television
cable network, the input mixer reduces the R&S FSH's inherent spurious products. However, the
inherent noise display of the R&S FSH increases due to the increased attenuation before the input
mixer.
In the R&S FSH3 models 1145.5850.03 and 1145.5850.23 and in the R&S FSH6, not only the RF
attenuation, but also the preamplifier, if switched on, is coupled to the reference level setting.
Preamplifier
OFF
Preamplifier
ON
Reference level
RF attenuation
RF attenuation
Preamplifier
Low Noise
Low Distortion
Low Noise
Low Distortion
-25 dBm
0 dB
0 dB
0 dB
0 dB
On
-24 dBm to -20 dBm
0 dB
0 dB
10 dB
10 dB
On
-19 dBm to -15 dBm
0 dB
10 dB
10 dB
10 dB
On
-14 dBm to -10 dBm
0 dB
10 dB
0 dB
10 dB
Off
-9 dBm to 0 dBm
10 dB
20 dB
10 dB
20 dB
Off
1 dBm to 10 dBm
20 dB
30 dB
20 dB
30 dB
Off
11 dBm to 20 dBm
30 dB
30 dB
30 dB
30 dB
Off
The status of the RF attenuation and the preamplifier can be queried in the Status menu (press the
STATUS key).
The reference level is in dBm for the default setting. However, the units dBmV, dB
O
V, Watt and Volt can
also be selected. Unit selection is of most relevance to the marker level display as the marker level is
displayed in the unit of the reference level.
A reference offset (REF OFFSET) can be defined for the reference level. The reference offset is a way
of increasing the reference level by a certain amount. This is useful if, for example, an attenuator or
amplifier has been inserted before the RF input. The R&S FSH automatically takes the loss or gain into
account when the level is displayed and no manual calculations are necessary. A loss introduced at the
RF input must be entered as a positive number and a gain as a negative number.
The measurement range (RANGE) determines the resolution along the level axis in the measurement
diagram. When the PRESET or default setting has been selected, the level axis is scaled in dB. The
measurement range is 100 dB or 10 dB per division (10 dB/DIV). The R&S FSH also provides the level
ranges 50 dB (5 dB/DIV), 20 dB (2 dB/DIV) and 10 dB (1 dB/DIV) which enhance resolution along the
level axis. However, increasing resolution does not increase the accuracy of, for example, the marker
level readout, but only makes it easier to read values off the trace. You can also select a linear level
