Vaisala RVP900, User Manual

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Table 29 Analysis Window Options
Option Recommended Use
Rectangular Included as a teaching tool.
Do not use for operation.
Hamming Best overall choice.
Blackman Useful for seeing plotted spectral components more than 40 dB below the strongest
signal present.
Useful in the
Pr
plot when a long span of data are available.
FIR filters designed with the Blackman window have a greater stopband attenuation
than those designed with the Hamming window, but the wider main lobe may be
undesirable.
Design/Analysis Window– 0:Rect , 1:Hamming, 2:Blackman : 1
The burst frequency estimator uses a fourth-order correlation model to estimate the center
frequency of the transmitted pulses. Each burst pulse typically occupies approximately 1
µsec. The frequency estimate feeding the AFC loop must be accurate to, perhaps, 10 KHz.
The accuracy for the question
Design/Analysis Window– 0:Rect , 1:Hamming,
2:Blackman : 1 cannot be achieved with only 1 pulse. However, several hundred
(unbiased) individual estimates can be averaged to produce an accurate mean. This
averaging is done with an exponential filter with the time constant chosen here.
Limits: 0.1 ... 120 s
Settling time (to 1%) of burst frequency estimator: 5.0 sec
AFC and MFC Parameters
AFC is required in magnetron systems to maintain the fixed intermediate frequency
difference between the transmitter and the STALO.
AFC is not required in klystron systems because the transmitted pulse is inherently at the
correct frequency.
Enable AFC and MFC functions: YES
The following AFC parameters appear only if you enable AFC and MFC functions.
You can configure the AFC servo loop to operate with an external Motor/Integrator
frequency controller, rather than the usual direct–coupled FM control.
Chapter 5 – TTY Non-volatile Setups
95