ETTC'2003 - SEE

1. INTRODUCTION
The gain versus frequency measurement allows to check the flatness of the
frequency response in the channel bandwidth.
It consists basically in sweeping the channel bandwidth by even frequency steps
and measuring the gain for each of these steps.
The functional test combined with the various configurations of the payload
channel allows to verify the good operating of nominal and redundant
equipment. This requirement is checked for each Receiving chain, and for each
Transmit chain.
This test is done in Fixed Gain Mode (FGM) with sufficient TWTA input back
off (IBO) so as to be in linear condition.
2. CONVENTIONAL METHOD
2.1 Measurement processing
This measurement is performed at small input power (close to 10 dB IBO) in
FGM mode to ensure that the TWTA’s work in linear mode.
First, the uplink carrier is set at its specified input power and at Channel center
frequency (CCF). The level tuning is made with a power meter (PM) and takes
into account the calibration factor of the relevant frequency.
For each frequency step, the input power level and output power level is
measured with a spectrum analyzer (ASA). Gain value is determined by
subtracting output level from input level.
Figure 1 and Figure 2 provide the results of a measurement of a channel with
SAW filter. The following parameters are applicable :
• Frequency range: channel bandwidth (2.7 MHz) and out of band
(± 0.6 MHz),
• Frequency step: 100 kHz.
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