Spectrum Measurements
R&S
®
ESRP
303
User Manual 1175.7445.02 ─ 08
Figure 6-10: Dependency of intermodulation level on useful signal 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.
Calculation method
It can be calculated from the known line slopes and the measured spacing a
D3
at a
given level according to the following formula:
N
D
P
a
IP
2
3
3
The 3
rd
order intercept point (TOI), for example, is calculated for an intermodulation of
60 dB and an input level P
U
of -20 dBm according to the following formula:
dBm
dBm
IP
10
)
20
(
2
60
3
Measurements
