User's Manual

RVP8 User’s Manual

October 2005

TTY Nonvolatile Setups

3–25

The mean power level of the burst is computed within the narrowed set of samples

that are used for AFC frequency estimation. The narrow subwindow will contain

only the active portion of the burst, and thus a mean power measurement is

meaningful. The full FIR window would include the leading and trailing pulse edges

and would not produce a meaningful average power. Since radar peak power tends to

be independent of pulse width, this single threshold value can be applied for all

pulsewidths.

Limits: –60 to +10 dBm.

Design/Analysis Window– 0:Rect, 1:Hamming, 2:Blackman : 1

You may choose the window that is used in 1) the design of the FIR matched filter,

and 2) the presentation of the power spectra for the various scope plots. Choices are

rectangular, Hamming, and Blackman; the Hamming window being the best overall

choice. The Blackman window is useful if you are trying to see plotted spectral

components that are more than 40dB below the strongest signal present. It is

especially useful in the “Pr” plot when a long span of data are available. FIR filters

designed with the Blackman window will have greater stopband attenuation than

those designed with the Hamming window, but the wider main lobe may be

undesirable. The rectangular window is included mostly as a teaching tool, and

should never be used in an operational setting.

Settling time (to 1%) of burst frequency estimator: 5.0 sec

The burst frequency estimator uses a 4

order correlation model to estimate the

center frequency of the transmitted pulses. Each burst pulse will typically occupy

approximately one microsecond; yet the frequency estimate feeding the AFC loop

needs to be accurate to, perhaps, 10KHz. Obviously this accuracy can not be

achieved using just one pulse. However, several hundred of the (unbiased) individual

estimates can be averaged to produce an accurate mean. This averaging is done with

an exponential filter whose time constant is chosen here.

Limits: 0.1 to 120 seconds.

Lock IFD sampling clock to external reference: NO

This question determines the usage of the shared SMA connector that is labeled

“AFC/(CLK)” on the RVP8/IFD. It is generally not necessary to phase lock the IFD

sampling clock to the radar system clock, since very good stability is obtained from

the burst phase measurements during normal operation. However, two cases that

benefit from clock locking are 1) using the RVP8 in a klystron system where an

external trigger is provided, and 2) dual-receiver systems in which computation of

is important.

The following two questions will appear only if you have requested that the IFD

sampling clock be locked to an external clock reference. See Section 2.2.12 for a

description of the hardware setups that must accompany this selection.