3-22 Carrier-to-Interference Spectrum Analyzer Measurements
3-112 PN: 10580-00447 Rev. H Spectrum Analyzer MG
3-22 Carrier-to-Interference
To select carrier-to-interference (C/I) measurement go to main menu and press MEASURE >
MEASUREMENT >C/I measurement. The C/I measurement is set up using the “SETUP Menu (C/I)”
on page 3-116.Carrier-to-interference (C/I) measurement is the ratio of the total RF power in the defined
integration bandwidth, including transmitter power, noise, interference and distortion, to the power in the
channel when the transmitter is turned off.
This measurement is commonly required in satellite downlink testing and land mobile radio (LMR) system
testing. In order to complete this measurement the carrier power should be turned off in a controlled way.
The C/I ratio is calculated as:
C/I = Carrier Power – Interference Power
The C/I can be measured by following the instructions below:
1. Select C/I under MEASUREMENT drop-down of MEASURE menu.
2. Select the SETUP menu.
3. Set the center frequency to the wanted transmitter’s center frequency value.
4. Set the span that enables a view of the full carrier channel with some additional margin.
5. Set the integration bandwidth for the measurement. This will typically be the channel bandwidth for the
signal standard under test.
6. Toggle on AUTO TIME to perform a single sweep at the maximum rate for measuring power when the
transmitter is on and off. Toggle off AUTO TIME when the noise, interference and distortion has a
significant time dependency. By setting a slow sweep time, the noise and interference from time variable
signals can be integrated in the measurement.
7. Connect the RF input to the signal under test with the wanted transmitter ON.
8. Start the measurement by selecting START MEAS.
9. When prompted, select CONTINUE to measure the carrier power.
10. To measure noise, interference and distortion over the same integration bandwidth turn off the
transmitter without disconnecting the RF connection.
11. Select CONTINUE to measure the noise, interference and distortion in the channel.
12. Select FINISH to complete the measurement, or CANCEL to stop the measurement.
13. Verify the measurement values such as Carrier power (transmitter ON), Interference power (Noise,
Interference and distortion (transmitter OFF), and the C/I ratio displayed in the C/I table.
Note
The C/I measurement is performed in a single sweep mode. To enable continuous sweep, toggle on
SWEEP Continuously button.
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