Rohde & Schwarz EMI Test ReceiverESCI - Page 312

MEAS - Analyzer R&S ESCI
1166.6004.12 4.180 E-1
Output
level
Intercept point
Intermodulation
product
Useful signal
Input level
Compression
1
1
1
3
Fig. 4-20 Dependence of intermodulation level on useful signal level
The useful signals at the twoport output increase proportionally with the input level as long as the
twoport 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 twoport 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 twoport output power.
It can be calculated from the known line slopes and the measured spacing a
D3
at a given level
according to the following formula.
IP
a
P
D
N
3
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:
IP dBm dBm3
60
2
20 10=+− =() .(4)
TOI
The TOI softkey enables the measurement of the 3
rd
order intercept point.
A two-tone signal with equal carrier levels is expected at the R&S ESCI 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.
The R&S ESCI calculates the third order intercept from the level spacing
between normal markers and delta markers and outputs it in the marker info
field.
IEC/IEEE-bus command:
CALC:MARK:FUNC:TOI ON;
CALC:MARK:FUNC:TOI:RES?