4-16
Setup and Operation
4
Observe the measured signal power and apply the appropriate correction factors from
Table 4-7 to obtain the true signal power:
Table 4-7
Correction factors for modulator output power measured in OPERATE mode
Criteria Correction
Factor
Comments
300 kHz resolution
bandwidth
4 dB
Because the RF-modulator output is a QPSK-modulated
waveform, its signal power is spread throughout the entire signal
bandwidth. The power measured in a 300 kHz portion of the
signal represents only a portion of the true power. At 300 kHz
resolution bandwidth, a correction factor of 4 dB is required for
compensation.
Spectrum analyzer with
sampled or
average-responding
detector
4 dB
Because different spectrum-analyzers detectors respond
differently to noise-like signals, the measured signal power can
vary. Sampled or averaged-responding detectors indicate a
lower power level than peak detectors. A correction factor of
4 dB is required to compensate for the difference in
measurement when using a sampled or average-responding
detector.
5
Adjust the RF-modulator output level relative to the analog-carrier level as necessary by
incrementing or decrementing the signal-level value on the modulator setup menu.
Spectrum Analyzer Procedure
⎯
Setting the Modulator Output Signal Level in 2T Test Mode
In the
2T TEST
mode, the RF modulator generates two test tones, one 1.024 MHz higher and one
1.024 MHz lower than the specified RF-modulator output frequency. These tones are CW
carriers whose signal level is equal to the level of the QPSK-modulated signal normally output
in OPERATE mode. By adjusting the signal level of these tones, you can accurately set the
RF-modulator output signal.
To set the RF-modulator output-signal level with the modulator in 2T Test mode:
1
Measure and record the analog-carriers signal level by observing the level of the carriers
during sync tip. During sync tip, the full signal power is concentrated in the carrier.
2
Connect the
RF OUT
of the OM 1000 to a spectrum analyzer and measure the power of the
modulator-output signal using a 300 kHz resolution bandwidth. Because this test mode
generates CW carriers, no correction factor need be applied to the measured power level.
3
Adjust the output level of the tone signal to approximately 15 dBmV below the
analog-carriers level. Change the signal level by incrementing or decrementing the signal
level value on the INTFC 6 (modulator setup) menu ranging from 0 through 40. This range
corresponds to an actual output-level range from +30 t50 dBmV. The default level
setting is 35, approximately 45 dBmV.
4
Reset the RF-modulator mode to OPERATE enabling normal operation after you adjust the
output level of the tone signals.
5
Select UP to display the MAIN menu if this is your final setup step.
OM 1000 Installation and Operation Manual
