Measurements and Results
R&S
®
FSVA3000/ R&S
®
FSV3000
294
User Manual 1178.8520.02 ─ 01
Figure 7-46: Dependency of intermodulation products on level of useful signals
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 quickly 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
However, the intercept point 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 third 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
Third Order Intercept (TOI) Measurement
