Baron Services DSSR-250C Pulsar Digital Solid-State Radar System User Manual

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RVP8 User’s Manual
March 2006
1.
Introduction and Specifications
Introduction and Specifications
The RVP8 Lineage
SIGMET Inc. has a 20-year history of supplying innovative, high-quality signal processing
products to the weather radar community. The history of SIGMET products reads like a history
of weather radar signal processing:
Year
Model
Units
Sold
1981
FFT
10
First commercial FFT-based Doppler signal processor for weather radar applications. Featured Simultaneous Doppler and intensity processing.
1985
RVP5
161
First single-board low-cost Doppler signal processor. First commercial application of dual PRF velocity unfolding algorithm.
1986
PP02
12
First high-performance commercial pulse pair processor with
18.75-m bin spacing and 1024 bins.
1992
RVP6
150
First commercial floating-point DSP-chip based processor. First
commercial processor to implement selectable pulse pair, FFT or
random phase 2nd trip echo filtering.
1996
RVP7
>200
First commercial processor to implement fully digital IF processing for weather radar.
2003
RVP8
Major Technical Milestones
First digital receiver/signal processor to be implemented using an
open hardware and software architecture on standard PC hardware under the Linux operating system. Public API’s are provided so that customers may implement their own custom processing algorithms.
Much of the proven, tested, documented software from the highly-successful RVP7 (written in
C) is ported directly to the new RVP8 architecture. This allows SIGMET to reduce
time-to-market and produce a high-quality, reliable system from day one. However, the new
RVP8 is not simply a re-hosting of the RVP7. The RVP8 provides new capabilities for weather
radar systems that, until now, were not available outside of the research community.
Advanced Digital Transmitter Option
For example, the RVP8 takes the next logical step after a digital receiver- a digitally synthesized
IF transmit waveform output that is mixed with the STALO to provide the RF waveform to the
transmitter amplifier (e.g., Klystron or TWT). The optional RVP8/Tx card opens the door for
advanced processing algorithms such as pulse compression, frequency agility and phase agility
that were not possible before, or done in more costly ways.
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Introduction and Specifications
Open Hardware and Software Design
Compared to previous processors that were built around proprietary DSP chips, perhaps the most
innovative aspect of the RVP8 is that it is implemented on standard PC hardware and software
that can be purchased from a wide variety of sources. The Intel Pentium/PCI approach promises
continued improvement in processor speed, bus bandwidth and the availability of low–cost
compatible hardware and peripherals. The performance of an entry level RVP8 (currently dual
2.4 GHz Pentium processors) is 6 times faster than the fastest RVP7 ever produced (with two
RVP7/AUX boards).
Aside from the open hardware approach, the RVP8 has an open software approach as well. The
RVP8 runs in the context of the Linux operating system. The code is structured and public API’s
are provided so that research customers can modify/replace existing SIGMET algorithms, or
write their own software from scratch using the RVP8 software structure as a foundation on
which to build.
The advantage of the open hardware and software PCI approach is reduced cost and the ability
for customers to maintain, upgrade and expand the processor in the future by purchasing
standard, low cost PC components from local sources.
SoftPlane High–Speed I/O Interconnect
There are potentially many different I/O signals emanating from the backpanel of the RVP8.
Most of these conform to well-known electrical and protocol standards (VGA, SCSI, 10–BaseT,
RS-232 Serial, PS/2 Keyboard, etc.), and can be driven by standard commercial boards that are
available from multiple vendors. However, there are other interface signals such as triggers and
clocks that require careful timing. These precise signals cannot tolerate the PCI bus latency. For
signals that have medium–speed requirements (~1 microsec latency) for which the PCI bus is
inappropriate; and others that require a high–speed (~ 1 ns latency) connection that can only be
achieved with a dedicated wire, the RVP8 Softplanet provides the solution.
Physically, the Softplanet is a 16-wire digital “daisy-chain” bus that plugs into the tops of the
RVP8/Rx, RVP8/Tx, and I/O boards. The wires connect to the FPGA chips on each card, and the
function of each wire is assigned at run–time based on the connectivity needs of the overall
system. The Softplanet allocates a dedicated wire to carry each high-speed signal; but groups of
medium-speed signals are multiplexed onto single wires in order to conserve resources. Even
though there are only 16 wires available, the Softplane is able to carry several high-speed signals
and hundreds of medium–speed signals, as long as the total bandwidth does not exceed about
600MBits/sec.
The Softplanet I/O is configured at run–time based on a file description rather than custom
wiring such as wirewrap. Neither the PCI backplane nor the physical Softplanet are customized
in any way. Since there is no custom wiring, a failed board can be replaced with a generic
off–the–shelf spare, and that spare will automatically resume whatever functions had been
assigned to the original board. Similarly, if the chassis itself were to fail, then simply plugging
the boards into another generic chassis would restore complete operation. Cards and chassis can
be swapped between systems without needing to worry about custom wiring.
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Introduction and Specifications
Standard LAN Interconnection for Data Transfer or Parallel Processing
For communication with the outside world, the RVP8 supports as standard a 10/100/1000 Base T
Ethernet. For most applications, the 100 BaseT Ethernet is used to transfer moment results (Z, T,
V, W) to the applications host computer (e.g., a product generator). However, the gigabit
Ethernet is sufficiently fast to allow UDP broadcast of the I and Q values for the purpose of
archiving and/or parallel processing. In other words, a completely separate signal processor can
ingest and process the I and Q values generated by the RVP8.
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RVP8 User’s Manual
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1.1
Introduction and Specifications
System Configuration Concepts
The hardware building blocks of an RVP8 system are actually quite few in number:
RVP8/IFDt IF Digitizer Unit- This is a separate sealed unit usually mounted in the
receiver cabinet. The primary input to the IFD is the received IF signal. In addition, the
IFD has channels to sample the transmit pulse and to take in an external clock to phase
lock the A/D conversion with the transmit pulse (not used for magnetron systems).
RVP8/Rxt Card- A PCI card mounted in the chassis. It connects to the IFD by a
CAT-5E cable which can be up to 25m long. In addition, there are two BNC trigger
outputs and four RS-422 programmable I/O signals.
I/O-62t Card and Connector Panel- These handle all of the various I/O associated
with a radar signal processor, such as triggers, antenna angles, polarization switch
controls, pulse width control, etc. The Connector Panel is mounted on either the front or
rear of the equipment rack and a cable (supplied) connects the panel to the I/O-62.
Optional RVP8/Txt card- This supplies two IF output signals with programmable
frequency, phase and amplitude modulation. In the simplest case it might merely supply
the COHO which is mixed with the STALO to generate the transmit RF for Klystron or
TWT systems. More interesting applications include pulse compression and frequency
agility scanning. This card is not necessary for magnetron systems.
PC Chassis and Processor with various peripherals- a robust 4U rack mount unit with
a dual-Xeon mother board, diagnostic front panel display, disk (mechanical or flash),
CDRW, keyboard, mouse and optional monitor for local diagnostic work. Redundant
power supplies are used, and there are redundant fans as well.
This modular hardware approach allows the various components to be mixed and matched to
support applications ranging from a simple magnetron system to an advanced dual polarization
system with pulse compression. Typically SIGMET supplies turn-key systems, although some
OEM customers who produce many systems purchase individual components and integrate them
by themselves. This allows OEM customers to put their own custom “stamp” on the processor
and even their own custom software if they so choose.
For the turnkey systems provided by SIGMET, the basic chassis is a 6U rack mount unit as
described above. A 2U chassis can be provided for applications for which space is limited. A
very low cost approach is to use a desk side PC, but this is not recommended for applications
that require long periods of unattended operation.
To illustrate various RVP8 configurations, some typical examples are shown below. For clarity,
all the examples show the single–board computer approach. A mother board approach is
equivalent.
Example 1: Basic Magnetron System
The building blocks required to construct the basic system are:
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Introduction and Specifications
RVP8 Configuration Example: Basic Magnetron System
Optional
Digital STALO
DAFC
Triggers
IF Signal
IF Magnetron Burst
IFD
COAX Uplink
Fiber Downlink
RVP8/Rx
ËËËËË
ËËËËË
ËËËËË
14-Bit
SBC
RS232C Antenna Angles
10/100 BaseT LAN Interface
Mouse
Utilities
Monitor
Keyboard
IFD- IF Digitizer installed in the radar receiver cabinet. This can be located up to 100 meters
from the RVP8 main chassis (fiber optic connection). The DAFC (Digital AFC) is an option to
interface to a digitally controlled STALO. Like the RVP7, the RVP8 provides full AFC with
burst pulse auto-tracking.
RVP8/Rx- The digital receiver collects digitized samples from the IFD and does the processing
to obtain I/Q. It also provides two trigger connections configurable for input or output.
SBC Card- Single Board Computer with dual SMP processors (PC) running Linux.
The figure above shows a basic magnetron system constructed with an IFD, and two PCI cards.
A standard RS-232 serial input (included with the SBC) is used for obtaining the antenna angles
and the output/input trigger is provided directly from the Rx card. This system has 5 times the
processing power of the fastest version of the previous generation processor (RVP7/Main board
plus 2 RVP7/AUX boards) so that it is capable of performing DFT processing in 2048 rangebins
with advanced algorithms such as random phase 2nd trip echo filtering and recovery.
Example 2: Klystron System with Digital Tx
In this case, the IFD can receive a master clock from the radar system (e.g., the COHO). This
ensures that the entire system is phase locked. As compared to the previous example there are
two additional cards shown in this example:
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Introduction and Specifications
RVP8 Configuration Example: High Performance Klystron
IF Signal
Reference Clock
IF Tx Waveform
IFD
14-Bit
RVP8/Rx
COAX Uplink
Fiber Downlink
Digitally Synthesized COHO
IF Tx Waveform
Pulse width
Triggers
Parallel or Synchro AZ
Connector Panel
Parallell or Synchro EL
10/100/1000 Base T
Mouse
Utilities
Monitor
ËËËË
I/OĆ62
ËËËË
SBC
ËËËË
ËËËË
RVP8/Tx
Keyboard
RVP8/Tx- The digital transmitter card provides the digital Tx waveform. A second output can be
used to provide a COHO in the event that the RVP8 is used to provide the system master clock.
In any case, the IF transit waveform and the A/D sampling are phase locked.
SIGMET I/O-62 card for additional triggers, parallel, synchro or encoder AZ and EL angle
inputs, pulse width control, spot blanking control output, etc. These signals are brought in via the
connector panel.
The figure shows the SIGMET SoftPlanet which carries time-critical I/O such as clock and
trigger information which is not appropriate for the PCI bus. These signals are limited to the
cards provided by SIGMET, i.e., the SoftPlanet is not connected to any of the standard
commercial cards.
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Introduction and Specifications
RVP8 Configuration Example: Dual Polarization Magnetron System
Optional
Digital STALO
Horizontal IF Signal
DAFC
IFD
COAX Uplink
14-Bit
IF Magnetron Burst
Horz
Fiber Downlink
Synch Clock
COAX Uplink
IFD
14-Bit
Vertical IF Signal
Fiber Downlink
Vert
Polarization Control
Pulse Width Control
Triggers
Connector Panel
Parallel or Synchro AZ
Parallell or Synchro EL
RVP8/Rx
ËËËË
I/OĆ62
ËËËË
SBC
ËËËË
ËËËË
RVP8/Rx
10/100/1000 BaseT LAN
Mouse
Utilities
Monitor
Keyboard
Example 3: Dual Polarization Magnetron System
In this system 2 IFD’s and two RVP8/Rx cards are used for the horizontal and vertical channels
of a dual-channel receiver. The legacy RVP7 technique of using a single IFD and two IF
frequencies for the horizontal and vertical channels (e.g., 24 and 30 MHz) is also supported by
the RVP8. In the case of either dual or single IFD’s, there is a synch clock provided by either the
STALO reference frequency (e.g., 10 MHz) or by the RVP8 itself.
The RVP8 supports calculation of the complete covariance matrix for dual pol, including ZDR,
PHIDP (KDP), RHOHV, LDR, etc. Which of these variables is available depends on whether the
system is a single–channel switching system (alternate H and V), a STAR system (simultaneous
transmit and receive) or a dual channel switching system (co and cross receivers). Note that for
the special case of a single channel switching system, only one IFD is required.
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Introduction and Specifications
COTS Accessories
Aside from the basic PCI cards required for the radar application, there are additional cards that
can be installed to meet different customer requirements, e.g.,
10/100–BaseT Ethernet card for additional network I/O (e.g., a backup network).
RS-232/RS-422 serial cards for serial angles, remote TTY control, etc.
Sound card to synthesize audio waveforms for wind profiler applications.
GPS card for time synch.
IEEE 488 GPIB card for control of test equipment.
The bottom line is that the PCI open hardware approach provides unparalleled hardware
flexibility. In addition, the availability of compatible low-cost replacement or upgrade parts is
assured for years into the future.
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March 2006
1.1.1
Introduction and Specifications
IFD IF Digitizer
The IFD 14-bit IF digitizer is a totally sealed unit for optimum low-noise
performance. The use of digital components within the IFD is minimized
and the unit is carefully grounded and shielded to make the cleanest
possible digital capture of the input IF signal. Because of this, the IFD
achieves the theoretical minimum noise level for the A/D convertors.
There are 4 inputs to the IFD:
IF video signal.
A secondary IF video signal, used for dual polarization or very
wide dynamic range applications.
IF Burst Pulse for magnetron or IF COHO for Klystron.
Optional reference clock for system synchronization. For a
Klystron system, the COHO can be input. Magnetron systems do
not require this signal. This clock can even come from the
RVP8/Tx card itself.
All of these inputs are on SMA connectors. The IF signal input is made
immediately after the STALO mixing/sideband filtering step of the
receiver where a traditional log receiver would normally be installed.
The required signal level for both the IF signal and burst is +6.5 dBm for
the strongest expected input signal. A fixed attenuator or IF amplifier
may be used to adjust the signal level to be in this range.
Digitizing is performed for both the IF signal and burst/COHO channels
at approximately 72 MHz to 14-bits. This provides 92 to 105 dB of
dynamic range (depending on pulse width) without using complex AGC,
dual A/D ranging or down mixing to a lower IF frequency.
All communication to the main RVP8 chassis goes over a special CAT5E
type cable. The major volume of data is the raw time series samples sent
down to the RVP8 Rx card. Coming back up is trigger timing and AFC
information to the IFD.
The RVP8 provides comprehensive AFC support for tuning the STALO of a magnetron system.
Alternatively, the magnetron itself can be tuned by a motorized tuning circuit controlled by the
RVP8. Both analog (+–10V) and digital tuning (with optional DAFC to 24 bits) are supported.
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RVP8 User’s Manual
March 2006
1.1.2
Introduction and Specifications
Digital Receiver PCI Card (RVP8/Rx)
The RVP8/Rx card receives the digitized IF samples from the IFD via the fiber optic
link. The advantage of this design is that the receiver electronics (LNA, RF mixer,
IF preamp, and IFD) can be located as far as 100–meters away from the RVP8 main
chassis. This makes it possible to choose optimum locations for both the IFD and the
RVP8, e.g., the IFD could be mounted on the antenna itself, and the processor box
in a nearby equipment room.
The RVP8/Rx is 100% compatible with the 14-bit RVP7/IFD, but it also includes
hooks for future IFD’s operating at higher sampling clock rates. Two additional BNC
connectors are included on the board’s faceplate. These can be used for trigger input,
programmable trigger output, or a simple LOG analog ascope waveform.
A remarkable amount of computing power is resident on the receiver board, in the
form of an FIR filter array that can execute 6.9 billion multiply/accumulate cycles
per second. These chips serve as the first stage of processing of the raw IF data samples. Their job is to perform the down–conversion, bandpass, and deconvolution
steps that are required to produce (I,Q) time series. The time series data are then transferred over the PCI bus to the SBC for final processing.
The FIR filter array can buffer as much as 80 microsec of 36MHz IF samples, and then compute
a pair of 2880–point dot products on those data every 0.83 microsec. This could be used to
produce over-sampled (I,Q) time series having a range resolution of 125–meters and a
bandwidth as narrow as 30Khz. The same computation could also yield independent 125–meter
time series data from an 80 microsec compressed pulse whose transmit bandwidth was
approximately 1MHz.
Finer range resolutions are also possible, down to a minimum of 25–meters. A special feature of
the RVP8/Rx is that the bin spacing of the (I,Q) data can be set to any desired value between 25
and 2000 meters. Range bins are placed accurately to within +2.2 meters of any selected grid,
which does not have to be an integer multiple of the sampling clock. However, when an integer
multiple (N x 8.333–meters) is selected, the error in bin placement effectively drops to zero.
Dual polarization radars that are capable of simultaneous reception for both horizontal and
vertical channels can be interfaced to the RVP8 using a separate RVP8/Rx and IFD for each
channel. Note that the multiplexed dual IF approach used for the RVP7 with a single IFD can
also be used.
One of the primary advantages of the digital receiver approach is that wide linear dynamic range
can be achieved without the need for complex AGC circuits that require both phase and
amplitude calibration.
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Introduction and Specifications
Calibration Plot for RVP8/IFD
The figure above shows a calibration plot for a 14-bit IFD with the digital filter matched to a 2
microsecond pulse. The performance in this case is >100 dB dynamic range.
The RVP8 performs several real time signal corrections to the I/Q samples from the Rx,
including:
Amplitude Correction- A running average of the transmit pulse power in the magnetron burst
channel is computed in real-time by the RVP8/Rx. The individual received I/Q samples are
corrected for pulse–to–pulse deviations from this average. This can substantially improve the
“phase stability” of a magnetron system to improve the clutter cancelation performance to near
Klystron levels.
Phase Correction- The phase of the transmit waveform is measured for each pulse (either the
burst pulse for magnetron systems or the Tx Waveform for coherent systems). The I/Q values
are adjusted for the actual measured phase. The coherency achievable is better than 0.1 degrees
by this technique.
Large Signal Linearization- When an IF signal saturates, there is still considerable information
in the signal since only the peaks are clipped. The proprietary large signal linearization
algorithm used in the RVP8 provides an extra 3 to 4 dB of dynamic range by accounting for the
effects of saturation.
The RVP8/Rx card provides the same comprehensive configuration and test utilities as the
RVP7, with the difference that no external host computer is required to run the utilities. These
utilities can be run either locally or remotely, over the network! Some examples are shown
below:
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Introduction and Specifications
Digital IF Band Pass Design Tool
The built–in filter design tool makes it easy for
anyone to design the optimal IF filter to match
each pulse width and application. Simply specify
the impulse response and pass band and the filter
appears. The user interface makes it easy to widen/narrow the filter with simple keyboard commands. There is even a command to automatically search for an optimal filter.
This display can also show the actual spectrum
of the transmit burst pulse for quality control and
comparison with the filter.
Burst Pulse Alignment Tool
The quality assessment of the transmit burst
pulse and its precise alignment at range zero
are easy to do, either manually using this tool
and/or automatically using the burst pulse
auto-track feature. This performs a 2D search
in both time and frequency space if a valid
burst pulse is not detected. The automatic
tracking makes the AFC robust to start–up
temperature changes and pulse width changes
that can effect the magnetron frequency.
AFC alignment/check is now much easier
since it can be done manually from a central
maintenance site or fully automatically.
Received Signal Spectrum Analysis Tool
The RVP8 provides plots of the IF signal versus
range as well as spectrum analysis of the signal
as shown in this example.
In the past, these types of displays and tools required that a highly-skilled engineer transport
some very expensive test equipment to the radar
site. Now, detailed analysis and configuration
can all be done from a central maintenance facility via the network. For a multi-radar network
this results in substantial savings in equipment,
time and labor.
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1.1.3
Introduction and Specifications
Mother Board or Single-Board Computer (SBC)
The dual-CPU Pentium mother board or single-board computer (SBC) acts as the host
to the Linux operating system and provides all of the compute resources for processing
the I/Q values that are generated by the RVP8/Rx card. Standard keyboard, mouse and
monitor connections are on the Rx backpanel, along with a 10/100/1000 BaseT Ethernet port. The system does not require that a keyboard, mouse or monitor be connected
which is typically the case at an unattended site. An SBC example is shown on the left.
Motherboards and SBC’s are available from many vendors, at various speeds Typically the SBC is equipped with 128 MB RAM. The RVP8 chassis has a front bay for either
a >20 GB hard disk or a Flash Disk. The Flash Disk approach is well suited to applications where high–reliability is important. CDRW is also provided for software maintenance. Note that the latest versions of the RVP8 software and documentation can always be down-loaded from SIGMET’s web site for FREE.
The SBC also plays host for SIGMET’s RVP8 Utilities which provide test, configuration, control and monitoring software as well as built–in on-line documentation.
1.1.4
Digital Transmitter PCI Card (RVP8/Tx)
Many of the exciting new meteorological applications for the RVP8 are made possible
by its ability to function as a digital radar transmitter. The RVP8/Tx PCI card synthesizes an output waveform that is centered at at the radar’s intermediate frequency. This
signal is filtered using analog components, then up–converted to RF, and finally amplified for transmission. The actual transmitter can be a solid state or vacuum tube device. The RVP8 can even correct for waveform distortion by adaptively “pre–distorting” the transmit waveform, based on the measured transmit burst sample.
The Tx card has a BNC output for the IF Tx waveform. In addition, there is a second
output for an auxiliary signal or clock, or for a clock input. At the bottom of the card
is a 9–pin connector for arbitrary I/O (e.g., TTL, RS422, additional clock).
The RVP8 digital transmitter finds a place within the overall radar system that exactly
complements the digital receiver. The receiver samples an IF waveform that has been
down–converted from RF, and the transmitter synthesizes an IF waveform for up–conversion to RF. The beauty of this approach is that the RVP8 now has complete control
over both halves of the radar, making possible a whole new realm of matched Tx/Rx
processing algorithms. Some examples are given below:
Phase Modulation- Some radar processing algorithms rely on modulating the phase of the
transmitter from pulse to pulse. This is traditionally done using an external IF phase modulator
that is operated by digital control lines. While this usually works well, it requires additional
hardware and cabling within the radar cabinet, and the phase/amplitude characteristics may not
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Introduction and Specifications
be precise or repeatable. In contrast, the RVP8/Tx can perform precise phase modulation to any
desired angle, without requiring the use of external phase shifting hardware.
Pulse Compression- There is increasing demand for siting radars in urban areas that also
happen to have strict regulations on transmit emissions. Often the peak transmit power is
limited in these areas; so the job for the weather radar is to somehow illuminate its
targets using longer pulses at lower power. The problem, of course, is that a simple long
pulse lacks the ability (bandwidth) to discern targets in range. The remedy is to increase
the Tx bandwidth by modulating the overall pulse envelope, so that a reasonable range
resolution is restored. The exceptional fidelity of the RVP8/Tx waveform can accomplish
this without introducing any of the spurious modulation components that often occur
when external phase modulation hardware is used.
Frequency Agility- This has been well studied within the research community, but has
remained out of the reach of practical weather radars. The RVP8/Tx changes all of this,
because frequency agility is as simple as changing the center frequency of the
synthesized IF waveform. Many new Range/Doppler unfolding algorithms become
possible when multiple transmit frequencies can coexist. Frequency agility can also be
combined with pulse compression to remedy the blind spot at close ranges while the long
pulse is being transmitted.
COHO synthesis- The RVP8/Tx output waveform can be programmed to be a simple
CW sine wave. It can be synthesized at any desired frequency and amplitude, and its
phase is locked to the other system clocks. If you need a dedicated oscillator at some
random frequency in the IF band, this is a simple way to get it.
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1.1.5
Introduction and Specifications
I/O-62 PCI Card and I/O Panel
The SIGMET I/O-62 is a short format PCI card that provides extensive I/O capabilities
for the RVP8. A typical installation would have one I/O-62 and an RVP8 Connector
Panel shown above. The Softplanet is used to interconnect the I/O 62 with other SIGMET PCI cards. Note that the identical card is used in the SIGMET RCP8 radar/antenna control processor which in general does not use the Softplanet connection. The
I/O-62 has a single 62-position, high-density “D” connector. This is attached to the
RVP8 Connector Panel (typically mounted on the front or back of the rack which holds
the RVP8). A standard 1:1 cable connects the remote panel to the I/O-62 card in the
RCP8 chassis. The standard connector panel provided by SIGMET meets the needs of
most radar sites.
The best part is that the I/O-62 is configurable in software, i.e., there is no need to open
the chassis to configure jumpers or switches. This means that when a spare board is
added, there is no need to perform hardware configuration or custom wiring.
The physical I/O lines are summarized in the system specifications section.
ESD Protection Features
Since the I/O lines are connected to the radar system, there is a potential for lightning or other
ESD type damage. This is addressed aggressively by the I/O-62 in two ways:
Every wire is protected by a Tranzorbt diode which transitions from an open to a full
clamp between ±27 to ±35 VDC. Additionally, the Connector Panel uses Tranzorbt
diodes on every I/O line for double protection.
High-voltage tolerant front-end receivers/drivers are used. All components connected to
the external pins can tolerate up to ±40V. For example, the TTL and wide range inputs
use protectors that normally look like 100 Ohm resistors, but open at high voltage.
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Introduction and Specifications
Run Time FPGA Configuration
The SIGMET I/O-62 card is built around a 100K–Gate FPGA which, in addition to driving the
I/O signals on the 62-position connector, also coordinates the PCI and Softplanet traffic. These
chips are SRAM–based, meaning that they are configured at run time. This allows the FPGA
code to be automatically upgraded during each RVP8 code release without needing to physically
reprogram any parts.
The board’s basic I/O services use up only 40% of the complete FPGA. The leftover space
makes it possible to add smart processing right on the I/O-62 board to handle custom needs. For
example the 16–bit floating–point (I,Q) data in the previous example could be reformatted into a
32–bit fixed–point stream. Other examples include generating custom serial formats, data
debouncing, and signal transition detection. In general, I/O functions that would either be
tedious or inappropriate for the host computer SBC can likely be moved onto the I/O-62 card
itself.
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Introduction and Specifications
1.2
Comparison of Analog vs Digital Radar Receivers
1.2.1
What is a Digital IF Receiver?
A digital IF receiver accepts the analog IF signal (typically 30 MHz), processes it and outputs a
stream of wide dynamic range digital “I” and “Q” values. These quantities are then processed to
obtain the moment data (e.g., Z, V, W or polarization variables). Additionally, the digital
receiver can accept the transmit pulse “burst sample” for the purpose of measuring the
frequency, phase and power of the transmit pulse. The functions that can be performed by the
digital receiver are:
IF band pass filtering
“I” and “Q” calculation over wide dynamic range
Phase measurement and correction of transmitted pulse for magnetron systems – from
burst sample
Amplitude measurement and correction of transmitted pulse – from burst sample
Frequency measurement for AFC output – from burst sample
The digital approach replaces virtually all of the traditional IF receiver components with flexible
software-controlled modules that can be easily adapted to function for a wide variety of radars
and operational requirements.
The digital receiver approach made a very rapid entry into the weather radar market. Up until
the about 1997 weather radars were not supplied with digital receivers. Today in 2003 nearly all
new weather radars and weather radar upgrades use the digital receiver approach. Much of this
rapid change is attributed to the previous generation RVP7 which is the most widely sold
weather radar signal processor of all time.
The number one advantage of a digital receiver is that it achieves a wide linear dynamic range
(e.g., >95dB depending on pulse width) without having to use AGC circuits which are complex
to build, calibrate and maintain. However, there are other advantages as well:
Lower initial cost by eliminating virtually all IF receiver components.
Lower life cycle cost do to reduced maintenance.
Selectable IF frequency.
Software controlled AFC with automatic alignment.
Programmable band pass filter
Dual or multiple IF multiplexing
Improved remote monitoring down to the IF level.
The following sections compare the digital receiver approach to the analog receiver approach.
This illustrates the advantages of the digital approach and what functions are performed by a
digital receiver.
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1.2.2
Introduction and Specifications
Magnetron Receiver Example
A typical analog receiver for a magnetron system is shown in the top portion of Figure 1–1. The
received RF signal from the LNA is first mixed with the STALO (RF–IF) and the resulting IF
signal is applied to one of several bandpass filters that match the width of the transmitted pulse.
The filter selection is usually done with relays. The narrow band waveform is then split. Half is
applied to a LOG amplifier having a dynamic range of 80–100dB, from which a calibrated
measurement of signal power can be obtained. The LOG amplifier is required because it is
almost impossible to build a linear amplifier with the required dynamic range. However, phase
distortion within the LOG amplifier renders it unsuitable for making Doppler measurements;
hence, a separate linear channel is still required.
The linear amplifier is fed from the other half of the bandpass filter split. It may be preceded by
a gain control circuit (IAGC) which adjusts the instantaneous signal strength to fall within the
limited dynamic range of the linear amplifier. The amplitude and phase characteristics of the
IAGC attenuator must be calibrated so that the “I” and “Q” samples may be corrected during
processing.
The IF output from the linear amplifier is applied to a pair of mixers that produce “I” and “Q”.
The mixer pair must have very symmetric phase and gain characteristics, and each must be
supplied with an accurate 0-degree and 90-degree version of the Coherent Local Oscillator
(COHO). The later is usually obtained by sampling a portion of the transmitted pulse, and then
phase locking an oscillator (COHO) that continues to “ring” afterward. Phase locked COHO’s
of this sort can be very troublesome – they often fail to lock properly, drift with age, and fail to
maintain coherence over the full unambiguous range.
The transmit burst that locks the COHO is also used by the Automatic Frequency Control (AFC)
loop. The AFC relies on an FM discriminator and low pass filter to produce a correction voltage
that maintains a constant difference between the magnetron frequency and the reference STALO
frequency. The AFC circuit is often troublesome to set and maintain. Also, since it operates
continuously, small phase errors are continually being introduced within each coherent
processing interval.
In contrast, the RVP8 digital receiver is shown in to lower portion of Figure 1–1. The only old
parts that still remain are the microwave STALO oscillator, and the mixer that produces the
transmit burst. The burst pulse and the analog IF waveform are cabled directly into the IFD on
SMA coax cables. Likewise, the AFC control voltage is also a simple direct connection either
with analog tuning (+–10V from IFD) or digital control via the optional DAFC interface. These
cables constitute the complete interface to the radar’s internal signals; no other connections are
required within the receiver cabinet.
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Introduction and Specifications
Figure 1–1:
Analog vs Digital Receiver for Magnetron Systems
Classic Analog Receiver for Magnetron
IF Filters Matched to
Pulse Widths
BPF
LOG
Analog RF
From LNA
Analog IF
BPF
Split
LOG
BPF
Digital Atten
BPF
Split
STALO
Quad Phase
Detector
AFC Signal
Linear Amp
Control Bits
From IAGC Logic
Line Drivers
Phase
Locked
IF
AFC
RF Tx Burst
IF Tx Sample
Split
IAGC
COHO
Low Q Locking COHO
RVP8 Magnetron Interface
Analog RF
From LNA
Split
Analog IF
IF
Digitizer
STALO
RF Tx Burst
RVP8/Rx
IFD
IF Tx Sample
Fiber Optic
Downlink
COAX
Uplink
+–10V Analog AFC
24 bits
Digital AFC Control
1–19
DAFC
Optional
ËËËË
RVP8 User’s Manual
March 2006
1.2.3
Introduction and Specifications
Klystron or TWT Receiver and Transmit RF Example
A typical analog receiver for a klystron system is shown in the top portion of Figure 1–2. The
arrangement of components is similar to the magnetron case, except that the COHO operates at a
fixed phase and frequency, a phase shifter is included for 2nd trip echo filtering and there is no
AFC feedback required. The phase stability of a Klystron system is better than a magnetron, but
the system is still constrained by limited linear dynamic range, IAGC inaccuracy, quad phase
detector asymmetries, phase shifter inaccuracies, etc.
The RVP8/Tx card now plays the role of a programmable COHO. The digitally synthesized
transmit waveform can be phase, frequency and amplitude modulated (no separate phase shifter
is required) and even produce multiple simultaneous transmit frequencies. These capabilities are
used to support advanced algorithms, e.g., range/velocity ambiguity resolution or pulse
compression for low power TWT systems.
Figure 1–2:
Analog vs Digital Receiver for Klystron Systems
Classic Receiver and Transmit RF for Klystron
BPF
LOG
Analog RF
Analog IF
BPF
Split
From LNA
LOG
BPF
Digital Atten
BPF
Split
Quad Phase
Detector
IAGC
Linear Amp
STALO
Control Bits
From IAGC Logic
Line Drivers
IF
Phase Shifter
Transmit RF
Δφ
COHO
To Klystron
Control Bits
Analog RF
RVP8 Klystron Interface
Analog IF
From LNA
Split
IF
Digitizer
STALO
Fiber Optic
Downlink
IFD
COAX
Uplink
IF Tx Sample
RF Tx Sample
Optional CLK
Transmit RF
To Klystron
Digital Synthesized IF (smart COHO)
1–20
RVP8/Rx
ËËËËË
ËËËËË
RVP8/Tx
ËËËËË
RVP8 User’s Manual
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Introduction and Specifications
1.3
RVP8 IF Signal Processing
1.3.1
IFD Data Capture and Timing
The RVP8 design concept is to perform very little signal processing within the IFD digitizer
module itself. This is to minimize the presence of digital components that might interfere with
the clean capture of the IF signals.
The digitized IF and burst pulse samples are multiplexed onto the fiber channel link which
provides the digital data to the RVP8/Main board at approximately 540-MBits/sec. The 14-bit
samples are encoded for transmission over a fiber channel link. This optical link allows the IFD
to be as far as 100 meters away from the RVP8/Main board and provides an added degree of
noise immunity and isolation.
The uplink input from the RVP8/Main board provides the timing for multiplexing the burst pulse
sample with the IF signal. In addition, it is used to set the AFC DAC or digital output level, and
to perform self tests.
The sample clock oscillator in the IFD is selected to be very stable. The sample clock serves a
similar function to the COHO on a traditional Klystron system, i.e., it is the master time keeper.
Because of this the IFD sample clock is used to phase lock the entire RVP8, i.e., the Rx, Tx,
IO-62 boards and the SoftPlane are all phase locked to the IFD sample clock. Designers have
two choices for factory configuration of the IFD sample clock:
A fixed crystal frequency selected to achieve a desired range resolution. The standard
range resolution corresponds to 25 m increments.
A very narrow band VCXO (50 ppm) selected to lock to an input reference signal from
the radar, and provide a desired range resolution. SIGMET stocks VCXO’s for 25 m
range resolution increments for reference inputs of 10, 20, 30 and 60 MHz. Custom
frequency VCXO’s are available on request. Examples of external reference signal
sources are an external COHO, external STALO reference or perhaps even a GPS clock).
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1.3.2
Introduction and Specifications
Burst Pulse Analysis for Amplitude/Frequency/Phase
The burst pulse analysis provides the amplitude, frequency and phase of the transmitted
pulse. The phase measurement is analogous to
the COHO locking that is performed by a traditional magnetron radar. The difference is that
the phase is known in the digital technique, so
that range dealiasing using the phase modulation techniques is possible. Amplitude measurement (not performed by traditional radars)
can provide enhanced performance by allowing the “I” and “Q” values to be corrected for
variations in the both the average and the pulseto-pulse transmitted power. In addition, a
warning is issued if the burst pulse amplitude
falls below a threshold value.
The burst pulse data stream is first analyzed by an adaptive algorithm to locate the burst pulse
power envelope (e.g. 0.8 msec). The algorithm first does a coarse search for the burst pulse in the
time/frequency domain (by scanning the AFC) and then does a fine search in both time and
frequency, to assure that the burst is centered at “range 0” and is at the required IF value. The
power-weighted phase of the burst pulse and the total burst pulse power is then computed. The
power weighted average phase is used to make the digital phase correction. Phase jitter for
magnetron systems with good quality modulator and STALO is better than 0.5 degrees RMS, as
measured on actual nearby clutter targets. For Klystron systems, the phase locking is better than
0.1 degree RMS.
The burst pulse frequency is also analyzed to calculate the frequency error from the nominal IF
frequency. For magnetron systems, the error is filtered with a selectable time constant which is
typically set to several minutes to compensate for slow drift of the magnetron. The digital
frequency error is sent via the uplink to the IFD in the receiver cabinet where a DAC converts it
into an analog output to the magnetron STALO. Optionally, a DAFC unit can be Teed off the
uplink cable to interface to Klystron systems do not require the AFC.
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1.3.3
Introduction and Specifications
Rx Board and CPU IF to I/Q Processing
Figure 1–3:
IF to I/Q Processing Steps
IF to I/Q Processing Steps
RVP8/Rx
Digital FIR
IFD Fiber Optic
Downlink
Fiber Optic
Receiver
Digitized IF Signal
and Tx Burst Sample
Bandpass Filter
Digital Quad Phase
and
Decompression
Digital IF
IF Tx Samples
IFD COAX
Uplink
I/Q
Signal
Digital AFC
Timing and digital AFC
I/Q Tx
Burst
PCI
CPU
AFC
Servo
Frequency
IF Tx
Samples
I/Q
Signal
Amplitude/
Phase
Correction
I/Q Moment
Processing
I/Q
Tx Burst
I/Q
Interference
Filter
I/Q
Time
Series
API
UDP Broadcast I/Q
Samples to recording
system or separate
processing system
Tx Burst Pulse
Analysis
1000 BaseT
Ethernet
The RVP8/Rx board performs the initial processing of the IF digital data stream and outputs “I”
and “Q” data values to the host computer via the PCI bus. In addition, the frequency, phase and
amplitude of the burst pulse are measured. The functions performed by the processor are:
Reception of the digital serial fiber optic data stream.
Band pass filtering of the IF signal using configurable digital FIR filter matched to the
pulsewidth.
Range gating and optional coherent averaging (essentially performed during the band
pass filtering step).
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Introduction and Specifications
Computation of “I” and “Q” quadrature values (also performed during the band pass
filtering step).
Transmit burst sample frequency, phase and amplitude calculation
I and Q phase and amplitude correction based on transmit burst sample.
Interference rejection algorithm.
AFC frequency error calculation with output to IFD for digital or analog control of
STALO (for magnetron systems).
The advantage of the digital approach is that the software algorithms for these functions can be
easily changed. Configuration information (e.g., processor major mode, PRF, pulsewidth, gate
spacing, etc.) is supplied from the host computer.
The digital matched filter that computes “I”
and “Q” is designed in an interactive manner using a TTY and oscilloscope for graphical display. The filter’s passband width
and impulse response length are chosen by
the user, and the RVP8 constructs the filter
coefficients using built-in design software.
The frequency response of the filter can be
displayed and compared to the frequency
content of the actual transmitted pulse.
Microwave energy can come from a variety of transmitters such as ground-based, ship-based or
airborne radars as well as communications links. These can cause substantial interference to a
weather radar system. Interference rejection is provided as standard in the RVP8. Three different
interference rejection algorithms are supported.
The RVP8/Rx board places the wide dynamic range “I” and “Q” samples directly on the PCI
bus where they are sent to the processor section of the PC (e.g., dual Pentium processors on a
single-board computer or motherboard). The I/Q values are then processed on the Pentium
processors to extract the moment information (Z, V, W and optional polarization parameters).
The I and Q values can also be placed on a gigabit Ethernet line (1000 BaseT) which is provided
directly on the processor board. This means that there is no second PCI bus “hit” required to
send the data to a recording system or a completely separate processing system.
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1.4
Introduction and Specifications
RVP8 Weather Signal Processing
The processing of weather signals by the RVP8 is based on the algorithms used in the previous
generation RVP7 and RVP6. However, the performance of the RVP8 allows a different approach
to some of the processing algorithms, especially the frequency domain spectrum processing. All
of the algorithms start with the wide dynamic range I and Q samples that are obtained from the
Rx card over the PCI bus.
The resulting intensity, radial velocity, spectrum width and polarization measurements are then
sent to a separate host computer to serve as input for applications such as:
Quantitative Rainfall Measurement
Vertical Wind Profiling
ZDR Hail Detection
Tornado Detection and Microburst Detection
Gust Front Detection
Particle Identification
Target Detection and Tracking
General Weather Monitoring
To obtain the basic moments, the RVP8 offers the option of several major processing modes:
Pulse Pair Mode Time Domain Processing
DFT/FFT Mode Frequency Domain Processing
Random Phase Mode for 2nd trip echo filtering
Polarization Mode Processing
Note that the RVP8 is the first commercial processor to perform discrete Fourier transforms
(DFT) as well as fast Fourier transforms (FFT). FFT is more computationally efficient than
DFT, but the sample size is limited to be a power of two (16, 32, 64, ...) This is too restrictive on
the scan strategy for a modern Doppler radar since this means, for example, that a one degree
azimuth radial must be constructed from say exactly 64 input I/Q values. The RVP8 has the
processing power such that when the sample size is not a power of 2, a DFT is performed instead
of an FFT
These modes share some common features that are described first, followed by descriptions of
the unique features of each mode.
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RVP8 User’s Manual
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1.4.1
Introduction and Specifications
General Processing features
Figure 1–4 shows a block diagram of the processing steps. These are discussed below.
Autocorrelations
The autocorrelations R0, R1 and R2 are produced by all three processing modes. However, the
way that they are produced is different for the three modes, particularly with regard to the
filtering that is performed.
Pulse Pair Mode — Filtering for clutter is performed in the time domain.
Autocorrelations are computed in the time domain.
DFT/FFT Mode — Filtering for clutter is performed in the frequency domain using both
fixed width filters and the Gaussian Model Adaptive Processing (GMAP) technique.
Autocorrelations are computed from the inverse transform.
Random Phase — Filtering for clutter and second trip echo is performed in the frequency
domain by adaptive algorithms. Autocorrelations are computed from the inverse
transform.
Figure 1–4:
I/Q Processing for Weather Moment Extraction
RVP8 Standard Moment Processing Steps
Time Series
API
Clutter Filter
Autocorrelations
Pulse Pair, FFT/DFT, Random Phase Modes
10/100/1000 BaseT
Ethernet
Thresholding
Speckle Filter
T0
R0
R1
R2
Clutter Micro
Suppression and
Range Averaging
SQI
LOG
SIG
CCOR
Moment and
Threshold
Calculations
T0
R0
R1
R2
To Applications Host Computer
The use of the R2 lag provides improved estimation of signal-to-noise ratio and spectrum width.
Processors that do not use R2 cannot effectively measure the SNR and spectrum width.
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Introduction and Specifications
Time (azimuth) Averaging
The autocorrelations are based on input “I” and “Q” values over a selectable number of pulses
between 8, 9, 10, ...,256. Any integer number of pulses in this interval may be used including
DFT/FFT and random phase modes.
Selectable angle synchronization using the input AZ and EL tag lines assures that all possible
pulses are used during averaging for each, say, 1 degree interval. This minimizes the number of
“wasted” pulses for maximum sensitivity. Azimuth angle synchronization also assures the
accurate vertical alignment of radial data from different elevation angles in a volume scan (see
below).
TAG Angle Samples of Azimuth and Elevation
During data acquisition and processing it is usually necessary to associate each output ray with
an antenna position. To make this task simpler the RVP8 samples 32 digital input “TAG” lines,
once at the beginning and once at the end of each data acquisition period. These samples are
output in a four-word header of each processed ray. When connected to antenna azimuth and
elevation, the TAG samples provide starting and ending angles for the ray, from which the
midpoint could easily be deduced. Since the bits are merely passed on to the user, any angle
coding scheme may be used. The processor also supports an angle synchronization mode, in
which data rays are automatically aligned with a user-defined table of positions. For that
application, angles may be input either in binary or BCD.
Range Averaging and Clutter Microsuppression
To improve the accuracy of the reflectivity measurements, the RVP8 can perform range
averaging. When this is done, autocorrelations from consecutive range bins are averaged, and
the result is treated as if it were a single bin. This type of averaging is useful to lower the
number of range bins that the host computer must process.
Range averaging of the autocorrelations may be performed over 2, 3, 4, ..., 16 bins. Prior to
range averaging, any bins that exceed the selectable clutter-to-signal threshold are discarded.
This prevents isolated strong clutter targets from corrupting the range average, which improves
the sub-clutter visibility.
Moment Extraction
The autocorrelations serve as the basis for the Doppler moment calculations,
Mean velocity – from Arg [ R1 ]
Spectrum width – from |R1| and |R2| assuming Gaussian spectrum
dBZ – from R0 with correction for ground clutter, system noise and gaseous attenuation.
Uses calibration information supplied by host computer.
dBT – identical to dBZ except without ground clutter.
These are the standard parameters that are output to the host computer on the high-speed
Ethernet interface.
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Introduction and Specifications
Thresholding
The RVP8 calculates several parameters that are used to threshold (discard) bins with weak or
corrupted signals. The thresholding parameters are:
Signal quality index (SQI=|R1|/R0)
LOG (or incoherent) signal-to-noise ratio (LOG)
SIG (coherent) signal-to-noise ratio
CCOR clutter correction
These parameters are computed for each range bin and can be applied in AND/OR logical
expressions independently for dBZ, V and W.
Speckle Filter
The speckle filter can be selected to remove isolated single bins of either velocity/width or
intensity. This feature eliminates single pixel speckles which allows the thresholds to be reduced
for greater sensitivity with fewer false alarms (speckles). Both a 1D (single azimuth ray) and 2D
(3 azimuth rays by 3 range bins) are supported.
Velocity Unfolding
A special feature of the RVP8 processor is its ability to “unfold” mean velocity measurements
based on a dual PRF algorithm. In this technique two different radar PRF’s are used for
alternate N-pulse processing intervals. The internal trigger generator automatically produces the
correct dual-PRF trigger, but an external trigger can also be applied. In the later case, the
ENDRAY_ output line provides the indication of when to switch rates. The RVP8 measures the
PRF to determine which rate (high or low) was present on a given processing interval, and then
unfolds based on either a 2:3, 3:4 or 4:5 frequency ratio. Table 1–1 gives typical unambiguous
velocity intervals for a variety of radar wavelengths and PRF’s.
Table 1–1:
Examples of Dual PRF Velocity Unfolding
Unambiguous Velocity (m/s) for
Various Radar Wavelengths
PRF1
PRF2
Unambiguous
Range (km)
3 cm
5 cm
10 cm
500
300
3.75
6.25
12.50
1000
150
7.50
12.50
25.00
2000
75
15.00
25.00
50.00
500
333
300
7.50
12.50
25.00
1000
667
150
15.00
25.00
50.00
2000
1333
75
30.00
50.00
100.00
1–28
No
f ldi
Unfolding
Two
Ti
Times
Unfolding
RVP8 User’s Manual
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Introduction and Specifications
PRF1
PRF2
Unambiguous
Range (km)
3 cm
5 cm
10 cm
500
375
300
11.25
18.75
37.50
1000
750
150
22.50
37.50
75.00
2000
1500
75
45.00
75.00
150.00
500
400
300
15.00
25.00
50.00
1000
800
150
30.00
15.00
100.00
2000
1600
75
60.00
100.00
200.00
1.4.2
Three Times
Unfolding
f ldi
Four
Times
Ti
Unfolding
RVP8 Pulse Pair Time Domain Processing
Pulse pair processing is done by direct calculation of the autocorrelation. Prior to pulse pair
processing, the input “I” and “Q” values are filtered for clutter using a a time domain notch
filter. Filters of various selectable widths are available for either 40 or 50 dB stop band
attenuation. The filtered I/Q values are processed to obtain the autocorrelation lags R0, R1 and
R2. The unfiltered power is also calculated (T0). The autocorrelations are then sent to the range
averaging and moment extraction steps.
1.4.3
RVP8 DFT/FFT Processing
The DFT/FFT mode allows clutter cancelation to be performed in the frequency domain. DFT is
used in general, with FFT’s used if the requested sample size is a power of 2.
Three standard windows are supported to provide the best match of window width to the
spectrum dynamic range:
Rectangular
Hamming
Blackman
Exact Blackman
Von Han
After the FFT step, clutter cancelation is done using a selectable fixed width filter that
interpolates across the noise or any overlapped weather or an adaptive filter which automatically
determines the optimal width. This technique preserves overlapped weather as compared to time
domain notch filters which will always attenuate overlapped weather to some extent, depending
on the spectrum width. After clutter cancelation, R0, R1 and R2 are computed by inverse
transform and these are used for moment estimation.
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1.4.4
Introduction and Specifications
Random Phase Processing for 2nd Trip Echo
Second trip echoes can be a serious problem for applications that require operation at a high
PRF. Second trip echoes can appear separately or can be overlaid on first trip echoes (second trip
obscuration). The random phase technique separates the first and second trip echoes so that:
In nearly all cases, the 2nd trip echo can be removed from the first trip even in the case
of overlapped 1st and 2nd trip echoes. The benefit is a clean first trip display.
The 2nd trip echoes can be recovered and placed at their proper range at 1st trip/2nd trip
signal ratios of up to 40 dB difference for overlapped echoes. Because of the wide
dynamic range of weather echoes, this power limit will sometimes be exceeded.
The technique requires that the phase of each pulse be random. Digital phase correction is then
applied in the processor for the first and second trips. The critical step is the adaptive filter
which removes the echo of the other trip to increase the SNR. Magnetrons have a naturally
random phase. For Klystron radars, a digitally controlled precision IF phase shifter is required.
The RVP8 provides an 8-bit RS422 output for the phase shifter.
For more information on the technique refer to Joe, et. al., 1995.
1.4.5
Polarization Mode Processing
Polarization processing uses a time domain autocorrelation approach to calculate the various
parameters of the polarization co-variance matrix, i.e., ZDR, LDR, PHIDP, RHOHV, PHIDP
(KDP), etc. In addition, the standard moments T, V, Z, W are also calculated. Which parameters
are available and which algorithms are used to calculate them depends on the type of
polarization radar, e.g., single channel switching, simultaneous transmit and receive (STAR),
dual channel switching. SIGMET, Inc. is licensed by US National Severe Storms Laboratory
(NSSL) to use the STAR hardware and processing techniques and algorithms.
Polarization measurements require special calibration of the ZDR and LDR offsets. The use of a
clutter filter for the polarization variables can sometimes bias the derived parameters. Because of
this, the user decides whether or not to use filtered or unfiltered time series.
1.4.6
Output Data
The RVP8 output data for standard moment calculations consist of mean radial velocity (V),
Spectrum Width (W), Corrected Reflectivity(Z or dBZ) and Uncorrected Reflectivity (T or
dBT). Other data outputs include I/Q time series, DFT/FFT power spectrum points and
polarization parameters. The output can be made in either 8 or 16-bit format. 8-bit format is
preferred over 16-bit format for most applications since the accuracy is more than adequate for
an operational radar system, and the data communications are reduced by 50%. 16-bit formats
are sometimes used by research customers for data archive purposes. Note that time series and
DFT are always 16-bit formats. All data formats are documented in Chapter 6 of this manual.
A standard output is the I/Q time series on gigabit network (1000 BaseT). These are sent via
UDP broadcast to an I/Q archiving system or even a completely independent parallel processing
system.
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Introduction and Specifications
1.5
RVP8 Control and Maintenance Features
1.5.1
Radar Control Functions
The RVP8 also performs several important radar control functions:
Trigger generation- up to 6 programmable triggers.
Pulsewidth control (four states controlled by four bits).
Angle/data synchronization- to collect data at precise azimuth intervals (e.g., every 0.5,
1, 1.5 degrees) based on the AZ/EL angle inputs.
Phase shifter- to control the phase on legacy Klystron systems. New or upgrade Klystron
or TWT systems can use the RVP8/Tx card to provide very accurate phase shifting.
ZDR switch control- for horizontal/vertical or other polarization switching scheme.
AFC output (digital or analog) based on the burst pulse analysis for magnetron systems.
Pulsewidth and trigger control are both built into the RVP8. Four TTL output lines can be
programmed to drive external relays that control the transmitter pulsewidth. The internal trigger
generator drives six separate lines, each of which can be programmed to produce a desired
waveform. The trigger generator is unique in that the waveforms are stored in RAM and can be
modified interactively by user software. Thus, precisely delayed and jitter-free strobes and gates
can easily be produced. For each pulsewidth there is a corresponding maximum trigger rate that
can be generated. Note, however, that the RVP8 can also operate from an external user-supplied
trigger. In either case, the processor measures the trigger period between pulses so that user
software can monitor it as needed.
The RVP8 also supports trigger blanking during which one or more (selectable) of the transmit
triggers can be inhibited. Trigger blanking is used to avoid interference with other electronic
equipment and to protect nearby personnel from radiation hazard. There are two techniques for
this:
2D AZ/EL sector blanking areas can be defined in the RVP8 itself.
An external trigger blanking signal (switch closure to ground, TTL or RS422) can be
supplied, for example from a proximity switch that triggers when the antenna goes below
a safe elevation angle or connected to the radome access hatch.
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RVP8 User’s Manual
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1.5.2
Introduction and Specifications
Power-Up Setup Configuration
The RVP8 stores on disk an extensive set of configuration information. The purpose of these
data is to define the exact configuration of the RVP8 upon startup. The setup information can be
accessed and modified using either a local keyboard and monitor, or over the network. For
multiple radar networks, the configuration management can be centrally administered by
copying tested “master” configuration files to the various network radars. It is not necessary to
go to the radar to change ROM’s as was the case for previous generation processors.
1.5.3
Built-In Diagnostics
On power-up, the RVP8 performs a sequence of internal self-tests. The test sequence requires
about four seconds to perform, and tests approximately 95% of the internal digital circuitry.
Errors are isolated to specific sections of the board as much as possible. If any check fails, the
user can be certain that some component is not functioning correctly. However, there is a very
small chance that even a defective board may pass all the tests; the failure may be in one of the
few areas that can not be checked.
The RVP8 displays the test results on the LED front panel (for a standard SIGMET chassis). In
this way, there is immediate visual confirmation of the diagnostic tests, even if the host computer
has not yet been connected. The local keyboard and monitor or a networked workstation can be
used to see the test results in the TTY menus or even invoke a power–up reset and test.
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RVP8 User’s Manual
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1.6
Introduction and Specifications
Support Utilities and Available Application Software
The RVP8 system includes a complete set of tools for the calibration, alignment and
configuration of the RVP8. These includes the following utilities:
ascope- a comprehensive utility for manual signal processor control and data display of
moments, times series and Doppler spectra. ascope includes a realistic signal simulator
capable of producing both first and second trip targets. Recording/playback of time
series and moments is included as well.
dspx- an ASCII text-based program to access and control the signal processor, including
providing access to the local setup menus.
speed- a performance measuring utility.
DspExport- exports the RVP8 to another workstation over the network. This allows
utilities on a remote network to run locally, as opposed to exporting the utility display
window over the network.
setup- interactive GUI for creating/editing the RVP8 configuration files.
zauto- calibration utility for use with a test signal generator.
These tools can be run locally on the RVP8 itself or over the network from a central maintenance
facility. The DspExport utility improves the performance of the utilities for network applications
by letting them be run on the workstation that is remote from the RVP8. Note that standard
X–Window export is of course supported but requires more bandwidth.
In addition, complete radar application software can be purchased from SIGMET:
IRIS/Radar on a separate PC, interfaces to the RVP8 by 100 BaseT Ethernet.
IRIS/Radar controls both the RVP8 and the SIGMET RCP8 radar/antenna control
processor. The package provides complete local and remote control/monitoring, data
processing and communication for a radar system.
IRIS/Analysis (and options) runs on a separate PC, often at a central site. One
IRIS/Analysis can support up to 20 radar systems. This functions as a radar product
generator (RPG) to provide outputs such as CAPPI, rain accumulations, echo tops,
automatic warning and tracking, etc. Optional software packages are provided for special
applications: wind shear and microburst detection, hydrometeorology with raingage
calibration and subcatchments, composite, dual Doppler and 3D Display.
IRIS/Web provides IRIS displays to network users on standard PC’s (Windows or
Linux) running Netscape or Internet Explorer.
IRIS/Display can display products sent to it and, with password authorization, can serve
as a remote control and monitoring site for networked radar systems. Features such as
looping, cross–section, track, local warning, annotation, etc. are all provided by
IRIS/Display. Note that both IRIS/Analysis and IRIS/Radar have all of the capabilities of
IRIS/Display in addition to their own functions. This means that any IRIS system can
display products.
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RVP8 User’s Manual
March 2006
1.7
Introduction and Specifications
System Network Architecture
The RVP8 provides considerable flexibility for network operation. This allows
remote control and monitoring of the system from virtually anywhere on the network,
subject to the user’s particular security restrictions.
Unlike the previous generation RVP7, which used a SCSI interface, the RVP8 uses a
network interface exclusively. The “dsp lib” runs locally on the RVP8 and a utility,
called DspExport, exports the library over the network using a TCP/IP socket.
Typically this is exported to a local host radar control workstation (RCW) on the
network. Perhaps this workstation is running the SIGMET IRIS software. At least
10BaseT connection is recommended for this connection.
Figure 1–5:
Network Architecture for Socket Interface with DspExport
Socket Interface Connections
RVP8
Local Keyboard, Mouse, Monitor
Mouse
Utilities
Monitor
Keyboard
Running
DspExport
TCPIP LAN 10BaseT or better
Local Host RCW
Utilities
Remote Workstation
Utilities
LAN or WAN TCPIP Netowrk
A remote workstation on the network can also use the DspExport technique to
communicate for configuration, monitoring and diagnostic testing.
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RVP8 User’s Manual
March 2006
1.8
Introduction and Specifications
Open Architecture and Published API
SIGMET recognizes that certain users may require the ability to write their own signal
processing algorithms which will run on the RVP8. To accommodate this, the RVP8 software is
organized to allow separately compiled plug-in modules to be statically linked into the running
code. The application program interface (API) allows user code to be inserted at the following
stages of processing:
Tx/Rx waveform synthesis and matched filter generation— The API allows the transmit
waveforms to be defined from pulse to pulse, along with the corresponding FIR
coefficients that will extract (I,Q) from that Tx waveform. This allows users to
experiment with arbitrary waveforms for pulse compression and frequency agility.
Time series and spectra processing from (I,Q)- The API allows you to modify the default
time series and spectra data, e.g., to perform averaging or windowing in a different way.
Parameter generation from (I,Q)- This is probably where the greatest activity will occur
for user–supplied code. The API allows you to redefine how the standard parameters
(dBZ, Velocity, Width, PHIDP, etc.) are computed from the incoming (I,Q) time series.
You may also create brand new parameter types that are not included in the basic RVP8
data set.
Note that the standard SIGMET algorithms are not made public in this model. Rather, the
interface hooks and development tools are provided so that users can add their own software
extensions to the RVP8 framework. Many of the library routines that are fundamental to the
RVP8 are also documented and can be called by user code; but the source to these routines is not
generally released. Development tools which are not under public license must be purchased
separately by the customer.
While most customers will use the signal processing software supplied by SIGMET, the new
open software architecture approach employed by the RVP8 will be very useful to those research
customers who want to try innovative new approaches to signal processing, or to those OEM
manufacturers who are interested in having their own “custom” stamp on the product.
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RVP8 User’s Manual
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Introduction and Specifications
1.9
RVP8 Technical Specifications
1.9.1
IFD Digitizer Module, Rev E or later
Input Signals
IF Received Signal: 50W, + 6.5 dBm full–scale, +20dBm absolute max
IF Burst or COHO: 50W, +6.5 dBm full–scale, +20dBm absolute max
Optional Reference Clock: 2–60 MHz –10 to 0 dBm
IF Ranges:
12—34 MHz, 38—70 MHz
Linear Dynamic Range
85 to >100dB depending on pulsewidth/bandwidth filter
A/D Conversion
Resolution
14 bit with jitter <2.5 picosec
Sampling rate
67 to 79 MHz (selectable, standard is 71.9364 MHz)
AFC Output
Analog –10 to +10V
Optional Digital AFC (DAFC) with up to 24 programmable output bits.
Automatic 2-D (time/frequency) burst pulse search and fine tracking algorithms.
IFD Link
Uses shielded CAT 5E cable, non standard signals, requires RVP8/Rx card, rev C or later.
Cable length to RVP8/Rx
2—25 meters, with automatic calibration of round trip time and range correction.
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RVP8 User’s Manual
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1.9.2
Introduction and Specifications
RVP8/Rx PCI Card, Rev C or later
Pulse Repetition Frequency
50 Hz to 20 KHz +0.1%, continuously selectable.
IF Band Pass Filter
Programmable Digital FIR with software selectable bandwidth. Built-in filter design
software with graphical user interface.
Impulse Response
Up to 3024 FIR filter taps, corresponding to 75 msec impulse response length for 72 MHz
IF samples at 125 meter range resolution. These very long filters are intended for use
with pulse compression.
Range Resolution
Minimum bin spacing of 25 meters selectable in N*8.33 meter steps. Bins can be
positioned in a configurable range mask with resolution of N* the fundamental bin
spacing, or arbitrarily to an accuracy of ±2.2 meters.
Maximum Range
Up to 1024 km
Number of Range Bins
Full unambiguous range at minimum resolution or 3096 range bins (whichever is less).
The RVP8 processor may only be fast enough to process an average of 50 meter bins.
Electrical Interfaces
CAT 5E cable from the IFD, rev E or later.
BNC #1 for trigger output (12V, 75W), or pretrigger input.
BNC #2 for trigger output (12V, 75W).
9-pin “D” connector supporting four RS-422 differential signals for miscellaneous input
and output with SoftPlanet support. Each line pair can operate as a transmitter or as a
receiver depending on what’s needed. Possible uses are: alternate reference clock input,
gating input for CW modes, additional trigger outputs, external phase shift requests, etc.
Data Output via PCI Bus
16-bit floating I and Q values
14-bit raw IF samples
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RVP8 User’s Manual
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1.9.3
Introduction and Specifications
RVP8/Tx PCI Card
Analog Waveform Applications
Digitally synthesized IF transmit waveform for pulse compression, frequency agility, and
phase modulation applications.
Master clock or COHO signal to the radar; can be phase locked or free running, arbitrary
frequency.
Analog Output Waveform Characteristics
Two independent, digitally synthesized, analog output waveforms (BNC). These two
outputs are electrically identical and logically independent IF waveform synthesizers that
can produce phase modulated CW signals, finite duration pulses, compressed pulses, etc.
Can drive up to +12dBm into 50W.
14-bit interpolating TxDAC provides 71dB Signal-to-Noise Ratio.
IF center frequency selectable from 8 to 32.4 MHz, and from 48.6 to 75MHz.
Signal bandwidth as large as 15MHz for wideband/multiband Tx applications. Band
width is adjustable in software.
Continuous or pulse modulated output with band width limiting on pulse modulation
output.
Precise phase shifting with transient band width limiting.
Total harmonic distortion less than –74dB.
Waveform pre-emphasis compensates for both static and dynamic Tx nonlinearities.
Other I/O signals
Clock In/Out 50W SMA connector. This can receive a CW reference frequency to which
the RVP8/Tx can lock to a P/Q frequency multiple (much like the RVP8/IFD can lock to
an external reference). This connector can also supply the TxData Clock, optionally
divided by some N between 1 and 16, in order to supply external circuitry with +10dBm
clock reference at 50W.
9-pin “D” connector supporting four RS-422 differential signals for miscellaneous input
and output with SoftPlanet support. Each line pair can operate as a transmitter or as a
receiver depending on what’s needed. Possible uses are: alternate reference clock input,
gating input for CW modes, additional trigger outputs, external phase shift requests, etc.
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RVP8 User’s Manual
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1.9.4
Introduction and Specifications
SIGMET I/O-62 PCI Card
Short format PCI card with 62-position “D” connector. Multiple cards may be installed.
Includes D/A, A/D, discrete inputs and outputs (TTL, wide range, RS422, etc.) See
summary table below.
I/O pin assignment mapping by softplane.conf file.
Standard or custom remote backpanels available.
ESD protection using Tranzorbt silicon avalanche diode surge suppression and
high-voltage tolerant components.
SIGMET I/O-62 Summary of Electrical Interfaces
Qty
Description
40
Lines configurable in groups of 8 to be either inputs or outputs. The electrical specifications are
software defined within each group as follows:
SSingle-ended TTL input or output with software–configured pull-up or pull-down
resistors for inputs.
SWide range inputs (27VDC, threshold +2.5VDC), often used for “lamp voltage”
status inputs.
SRS-422/485 @ 10 MBit/sec (requires two lines each).
RS-422 receivers can be configured in software to have 100W termination between
each pair.
A/D convertors configurable as 0, 4, or 8 convertors, 2V, 12 bits @ 10 MHz, These lines are
shared with some of the 40 I/O lines listed above.
D/A convertors, 10V 1 MHz update rate, output can drive a 75W load.
SPDT relays on the board. These are often used for switching high power relays. Contacts are
diode protected.
RS-232C full duplex lines (Tx and Rx)
12V 75W trigger drivers .
Power/Ground pairs of 12V power (filtered, fused) for external equipment or remote backpanel
use (up to 24 W total). Polyfuse technology acts like a circuit breaker with auto reset in the event
of an overload.
Ground wires for signal grounds from the remote back panel.
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RVP8 User’s Manual
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1.9.5
Introduction and Specifications
I/O-62 Standard Connector Panel
Mounts on front or rear of standard 19” EIA rack
Connects to I/O-62 via 1:1 62–pin 1.8–m cable (provided).
Provides standard inputs and outputs required by most weather radars such as triggers,
polarization control, pulse width control and antenna angles.
Az and El synchro and reference inputs (nominal 100V 60 Hz)
3 internal relays and 4 12V relay control signals for switching external devices.
Programmable scope test points with source waveforms selectable in software.
Diagnostic power supply and self test LED’s for troubleshooting.
RVP8 Connector Panel Summary
J-ID
Label
Type
Description
J1
AZ INPUT
DBF25
Up to 16–bits of parallel TTL binary or BCD angle
J2
AZ OUTPUT
DBF25
Up to 16–bits of parallel TTL binary or BCD angle
J3
PHASE OUT
DBF25
Up to 8–bits of parallel TTL or RS422. Angles are configurable.
J4
EL INPUT
DBF25
Up to 16–bits of parallel TTL binary or BCD angle
J5
EL OUTPUT
DBF25
Up to 16–bits of parallel TTL binary or BCD angle
J6
RELAY
DBF25
3 internal relays, contact rating 0.5 A continuous. The switching
load is 0.25 A and 100V, with the additional constraint that the total
power not exceed 4VA.
4, 12V relay control signals, up to 200mA.
(Note that external relays should be equipped with proper diode
protection to shunt the back EMF).
J7
SPARE
DBF25
20 additional TTL I/O lines each configurable to be input or output.
J8
SPARE
DBF25
10 differential analog inputs, up to ±20V max multiplexed into A/D
convertor sampling each at >1000 Hz.
J9
MISC I/O
DBF25
7 additional RS422 lines and 2 each dedicated (non–multiplexed)
A/D inputs (±580V with pot adjust) and D/A outputs (±10V).
J10
SERIAL
DBF9
RS232C
J11
SERIAL
DBF9
RS232C
J12
S–D
Modular
3 x 4 matrix connector for AZ and EL synchro and reference inputs
J13
TP–1
BNC
Programmable scope test point. 75 Ohms
J14
TP–2
BNC
Programmable scope test point. 75 Ohms
J15
TRIG–1
BNC
12V trigger into 75 Ohms
J16
TRIG–2
BNC
12V trigger into 75 Ohms
J17
TRIG–3
BNC
12V trigger into 75 Ohms
J18
TRIG–4
BNC
12V trigger into 75 Ohms
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RVP8 User’s Manual
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1.9.6
Introduction and Specifications
RVP8 Processing Algorithms
Input from Rx Board
16–bit I/Q samples
Optional dual-channel I/Q samples (e.g., for polarization systems or dual frequency
systems)
IQ Signal Correction Options
Amplitude jitter correction based on running average of transmit power from burst pulse.
Interference correction for single pulse interference
Saturation correction (3 to 5 dB)
Primary Processing Modes
Poly-Pulse Pair (PPP)
DFT
Random or Phase Coded 2nd trip echo filtering/recovery
Optional Polarization with full co-variance matrix (ZDR, PHIDP, LDR, RHOHV, etc.)
Optional Pulse Compression
Processing Options
FIR Clutter filters (40 and 50 dB) in pulse pair mode.
Adaptive width clutter filters in DFT and phase coded 2nd trip mode.
Velocity De-Aliasing: Dual PRF Velocity unfolding at 3:2, 4:3 and 5:4 PRF ratios or
Dual PRT Velocity processing for selectable inter-pulse intervals.
Range De-aliasing:
Scan angle synchronization for data acquisition.
Pulse integration up to 1024
Corrections for gaseous attenuation and 1/R2.
Up to 4 pulse widths
Phase coding method (random phase for magnetron)
Frequency coding method (not available for magnetron)
Data Outputs
dBZ
Calibrated equivalent radar reflectivity, 8 or 16 bits
Mean radial velocity, 8 or 16 bits
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RVP8 User’s Manual
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Introduction and Specifications
Spectrum width, 8 or 16 bits
I/Q
Time series, 16 bits each per sample
DFT
Doppler Spectrum output option in DFT mode, 16 bits per component
Optional:
ZDR, PHIDP, RHOHV, LDR, RHO, 8 or 16 bits
Data Quality Thresholds
Signal–to–noise ratio (SNR) Used to reject bins having weak signals.
Typically applied to dBZ.
Signal quality index (SQI)
Clutter-to-signal ratio (CSR) Used to reject range bins having very strong clutter.
Typically applied to mean velocity, width and dBZ.
Speckle Filter
Used to reject bins having incoherent signals.
Typically applied to mean velocity and width.
Filter removes single-bin targets such as aircraft or noise
Fills isolated missing pixels as well.
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RVP8 User’s Manual
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1.9.7
Introduction and Specifications
RVP8 Input/Output Summary
Ethernet Input/Output from Host Computer
Data output of calibrated dBZ, V and W during normal operation. Full I/Q timeseries
recording with a separate tsarchive utility, or through a customer’s application using a
public API. Signal processor configuration and verification read–back is performed via
the Ethernet interface.
RS-232C Serial Data I/O
For real time display/monitoring or data remoting.
AZ/EL Angle Input Options
Serial AZ/EL angle tag input using standard SIGMET RCP format.
16-bit each parallel TTL binary angles via the I/O-62 card.
Synchro angle inputs via the I/O-62 card.
SIGMET network antenna packet protocol.
Trigger Output
Up to 10 total triggers available on various connector pins. Triggers are programmable
with respect to trigger start, trigger width and sense (normal or inverted).
Optional Polarization Control
RS-422 differential control for polarization switch.
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RVP8 User’s Manual
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1.9.8
Introduction and Specifications
Physical and Environmental Characteristics
Packaging
Motherboard Configuration
Custom PC configurations available or packaged by customer.
Dimensions of standard 4U chassis
43.2 wide x 43.2 long x 17.8 cm high
17 wide x 17 long x 7.00 inch high
Dimensions IF Digitizer
2.5 wide x 10.9 long x 23.6 cm high
1 wide x 4.3 long x 9.3 inch high
Redundant Power Supplies. Three hot–swap modules with audio failure alarm.
4U rack mount with 6 PCI slots
Input Power
IFD
Main Chassis 60/50 Hz 115/230 VAC Manual Switches
100–240 VAC 47–63 Hz auto–ranging
Power Consumption
RVP8/Main Processor
180 Watts with Rx and Motherboard
RVP8/IFD IF Digitizer
12 Watts
Environmental
Temperature
0C (32F) to 50C (122F)
Humidity
0 to 95% non–condensing
Reliability
MTBF>50,000 hours (based on actual RVP7 field data).
1–44

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