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Functions and Measurements
Making Distortion Measurements
Third-Order Intermodulation Distortion
Remote
Standby
On
N O T E
56
Two-tone, third-order intermodulation distortion is a common
specification in communication systems. When two signals are
present in a non-linear system, they may interact and create
third-order intermodulation distortion (TOI) products that are
located close to the original signals. System components such as
amplifiers and mixers contribute to the generation of these
distortion products.
This example will test a device for third-order intermodulation
through the use of markers. Two sources are used, one set to 300
MHz and the other to 301 MHz.
1
Connect the equipment as shown in figure below. This combination
of signal generators, low pass filters, and directional coupler (used
as a combiner) results in a two-tone source with very low
intermodulation distortion. Although the distortion from this setup
may be better than the specified performance of the analyzer, it is
useful for determining the TOI performance of the source/analyzer
combination. After the performance of the source/analyzer
combination has been verified, the device-under-test (DUT) (for
example, an amplifier) would be inserted between the directional
coupler output and the analyzer input.
Signal Generator
FUNCTIONS
N9310A
RF Signal Generator 9 kHz - 3.0 GHz
Frequency
AM
I/ Q
Utility
Preset
Amplitude
FM
Sweep
File
Local
Enter
M
Pulse
Trigger
LF Out
7
8
9
MOD
On/ Off
4
5
6
1
2
3
¡¤
0
RF
On/ Off
LF OUT
RF OUT 50
REVERSE PWR
4W MAX 30VDC
RF OUT
300 MHz low
pass filter
The coupler should have a high degree of isolation between the two input
ports so the sources do not intermodulate each other.
Signal Generator
FUNCTIONS
N9310A
RF Signal Generator 9 kHz - 3.0 GHz
Frequency
AM
I/ Q
Utility
Preset
Amplitude
FM
Sweep
File
Local
Enter
M
Pulse
Trigger
LF Out
7
8
9
MOD
On/ Off
4
5
6
1
2
3
¡¤
0
RF
On/ Off
Remote
Standby
LF OUT
RF OUT 50
On
REVERSE PWR
4W MAX 30VDC
300 MHz
low pass
filter
Directional Coupler
Spectrum Analyzer
N 9320A
SPECTRUM AN ALYZER
9 kHz - 3.0 GHz
Auto
BW /
Sw eep/
Tune
Avg
Trig
Local
View /
Det/
File/
M arker
Trace
Display
Print
Save
Peak
MODE
Meas
M arker
Search
7
8
9
4
5
6
1
2
3
Back
0
·
Enter
Rem ote
50V DC M AX
30dBm 1W M AX
Standby
TG SOURCE
CAL OU T
RF IN 50
On
PROBE POWER
50M Hz 10dBm
CAT Ⅱ
RF IN
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