Vaisala RVP900, Руководство пользователя

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Figure 37 Linearization of Saturated Signals Above +8 dBm
7.2.7 Amplitude Correction for Tx Power Fluctuations
RVP900 can perform pulse-to-pulse amplitude correction of the digital (
I
,
Q
) data stream
based on the amplitude of the Burst/COHO input. The technique computes a (real valued)
correction factor at each pulse by dividing the mean amplitude of the burst by the
instantaneous amplitude of the burst. The (
I
,
Q
) data for that pulse are then multiplied by
this scale factor to obtain corrected time series. The amplitude correction is applied after the
Linearized Saturation Headroom correction.
Instantaneous amplitude correction is a unique feature of the RVP900 digital receiver.
Bench tests with a signal generator reveal that an amplitude modulated waveform having
2.0 dB of pulse-to-pulse variation is reduced to less than 0.02 dB RMS of (
I
,
Q
) variation
after applying the amplitude correction.
The mean burst amplitude is computed by an exponential average whose (1/e) time
constant is selected as a number of pulses. See
5.2.4 Mp — Processing Options (page 107) .
A short time constant settles faster, but is not be as thorough in removing amplitude
variations (since the mean itself varies). Longer time constants do a better job, but require a
few seconds before valid data is available when the transmitter is first turned on. The default
value of 70 gives excellent results in almost all cases.
RVP900 User Guide M211322EN-J
182