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testing, they can be useful in isolating specific faults. Table 5-3 summarizes the modulator port
test modes.
Table 5-3
Modulator port testing modes
Mode
Description
CW test
The RF modulator generates a single CW signal. The signal frequency is exactly the same as
the center frequency of the QPSK-modulated signal. The signal level is equal to the
composite level of the QPSK signal. This mode is useful for rough level setting and for exact
frequency measurements.
2T test
The RF modulator generates two tones 1.024 MHz above and below the carrier frequency.
The level of each tone is 1 dB below the level of the modulated QPSK signal. The composite
RMS level of both tones together is 2 dB above the level of the QPSK modulator signal. This
mode is useful for setting levels using a spectrum analyzer with a 30 to 300 kHz resolution
bandwidth to resolve the two tones. If the level of each tone is set to the desired
QPSK-operating level, the actual QPSK operating level is 1 dB higher, providing 1 dB of extra
margin to the link.
CON test
The RF modulator operates the same as in the Operate mode, except that the digital FIR
filter coefficients are changed. In the Operate mode, the FIR filter frequency-response shape
is rectangular. In the CON Test mode, the FIR filter frequency-response shape is a raised
cosine with an alpha value equal to 0.5. This mode is useful for testing using a constellation
or vector analyzer.
Troubleshooting
OM 1000 Installation and Operation Manual
5-3
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