User's Manual

RVP8 User’s Manual
October 2005
TTY Nonvolatile Setups
3–9
Minimum freerunning ray holdoff: 100% of dwell
This parameter controls the rate at which the RVP8 processes free-running rays. This
prevents rays from being produced at the full CPU limit or I/O limit of the processor
(whichever was slower); which could result in highly overlapping data being output
at an unusably fast rate. Note that this behavior will only occur when running
without angle syncing, such as during IRIS Manual and RHI scans.
To make these free-running modes more useful, you may establish a minimum
holdoff between successive rays, expressed as a percentage of the number of pulses
contributing to each ray. Choosing 100% (the default) will produce rays whose input
data do not overlap at all, i.e., whose rate will be exactly the PRF divided by the
sample size. Choosing 0% will give the unregulated behavior in which no minimum
overlap is enforced and rays may be produced very quickly.
Limits: 0 to 100%
Linearized saturation headroom: 4.0 dB
The RVP8 uses a statistical saturation algorithm that estimates the real signal power
correctly even when the IF receiver is overdriven (i.e., for input power levels above
+4dBm). The algorithm works quite well in extending the headroom above the top
end of the A/D converter, although the accuracy decreases as the overdrive becomes
more severe. This parameter allows you to place an upper bound on the maximum
extrapolation that will ever be applied. Choosing 0dB will disable the algorithm
entirely.
Limits: 0 to 5dB
Apply amplitude correction based on Burst/COHO: YES
Time constant of mean amplitude estimator: 70 pulses
The RVP8 can perform pulse-to-pulse amplitude correction of the digital (I,Q) data
stream based on the amplitude of the Burst/COHO input. Please see Section 5.1.7 for
a complete discussion of this feature.
Limits: 10 to 500 pulses
IFD built–in noise dither source: –57.0dBm
This question will only appear if the processor is attached to a Rev.D RVP8/IFD that
includes an out-of-band noise generator to supply dither power for the A/D
converters. The available power levels are { Off, –57dBm, –37dBm, –32dBm,
–27dBm, –22dBm, –19dBm }. The closest available level to your typed-in value will
be used. You can observe the band-limited noise easily in the Pr plot to confirm its
amplitude and spectral properties.
For standard operation, we recommend running at –57dBm. The problem higher
levels of dither level is that, for certain choices of (I,Q) FIR filter, the stopband of the
filter may not give enough attenuation to preserve the RVP8/IFD’s inherent noise
level. For example, the factory default 1MHz bandwidth Hamming filter has a
stopband attenuation near DC of approximately 43dB. You can see this graphically at
the right edge of the Ps menu. The in-band contribution of dither power is therefore
approximately (–37dBm) – 43dB = –80dBm, which exceeds the A/D converter’s
1MHz bandwidth noise of –81.5dBm.