Chapter 5 _______________________________________________________ Plot-Assisted Setups
VAISALA______________________________________________________________________ 149
5.3.4 Recommended Adjustment
Procedures
The burst pulse timing must be calibrated separately for each individual
pulse width. Repeat the following procedure for each pulse width that you
plan to use. Each iteration is independent.
It is first necessary to setup the proper relative timing for all RVP900
triggers that are being used. The various trigger output lines are completely
interchangeable, and each may be assigned to any function within the radar
system. For example, Trigger #1 might be the transmitter pretrigger,
Triggers #3 and #4 might synchronize external displays, and Triggers #2,
#5, and #6 might be unused.
Choose an initial impulse response length of 1.5 times the transmit pulse
width. This length is refined later when the matched filter is designed (See
Section 5.4 Ps — Plot Burst Spectra and AFC on page 148). Adjust the plot
time span to view a small region around the sample window, and set the
initial amplitude zoom to x16. This assures that the plotted waveform is
still noticeable, even if the burst signal strength is very weak.
Verify that the transmitter is radiating, and observe the burst pulse samples
on the display. Use the L and R commands to shift the timing of all six
triggers relative to range zero. This has the effect of moving the burst
sampling window relative to the transmitted pulse. Depending on whether
Pwr Indicates the mean power within the full window of burst
samples. DC offsets in the A/D converter do not affect the
computation of the power, that is, the value shown truly
represents the waveform's (Signal+Noise) energy.
DC Indicates the nominal DC offset of the burst pulse A/D
converter. This is of interest only as a check on the
integrity of the front end analog components. The value
should be in the range ±2.0%.
Trig#1 Indicates the starting time of the first RVP900 trigger
outputs. This number varies as the L and R subcommands
cause the triggers to slew left and right. If the radar
transmitter is directly fired by an external pretrigger, the
pretrigger delay (in the form "PreDly:6.87") is printed
instead.
BPT This shows the present value of timing slew (measured in
microseconds) being applied to track the burst. The slew is
zero initially when the RVP900 is first powered up,
meaning that the normal trigger start times are all being
used.
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