R&S FSQ Signal Analyzer - Rohde & Schwarz

R&S FSQ Instrument Functions
Analyzer Mode
The level of the intermodulation products depends on the level of the useful signals.
If the two useful signals are increased by 1 dB, the level of the intermodulation products
increases by 3 dB, which means that spacing aD3 between intermodulation signals
and useful signals is reduced by 2 dB. This is illustrated in Fig. 4.15
Dependence of intermodulation level on useful signal level.
Output
level
Compression
Useful signal
1
1 1
Intermodulation
product
Intercept point
Fig. 4.15 Dependence of intermodulation level on useful signal level
Input level
The useful signals at the two port output increase proportionally with the input level
as long as the two port is in the linear range. A level change of 1 dB at the input
causes a level change of 1 dB at the output. Beyond a certain input level, the two
port goes into compression and the output level stops increasing. The intermodulation
products of the third order increase three times as much as the useful signals.
The intercept point is the fictitious level where the two lines intersect. It cannot be
measured directly since the useful level is previously limited by the maximum two
port output power.
It can be calculated from the known line slopes and the measured spacing aD3 at a
given level according to the following formula.
IP3 =
aD3 -------- + P
2 N
The 3 rd order intercept point (TOI), for example, is calculated for an intermodulation
of 60 dB and an input level PU of -20 dBm according to the following formula:
60
IP3 – ----- +
( – 20dBm)
– 10dBm
2
TOI The TOI softkey enables the measurement of the 3rd order intercept point.
A two-tone signal with equal carrier levels is expected at the R&S FSQ input.
MARKER 1 and MARKER 2 (both normal markers) are set to the maximum of the
two signals. MARKER 3 and MARKER 4 (both delta markers) are placed on the
intermodulation products. When the function is enabled, the frequency entry is activated
for the delta markers. They can be set manually.
Operating Manual 1313.9681.12 - 01 4.123
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