Baron Services DSSR-250C Introduction and Specifications
RVP8 User’s Manual
March 2006
Introduction and Specifications
1. 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:
Units
Year
1981 FFT 10 First commercial FFT-based Doppler signal processor for weath-
1985 RVP5 161 First single-board low-cost Doppler signal processor. First com-
Model
Sold
Major Technical Milestones
er radar applications. Featured Simultaneous Doppler and intensity processing.
mercial 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 process-
ing for weather radar.
2003
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
RVP8 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.
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 Softplane
t 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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Introduction and Specifications
1.1 System Configuration Concepts
The hardware building blocks of an RVP8 system are actually quite few in number:
S 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).
S 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.
S 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.
S 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.
S 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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RVP8 Configuration Example: Basic Magnetron System
Introduction and Specifications
Optional
DAFCDigital STALO
IF Signal
IF Magnetron Burst
IFD Fiber Downlink
14-Bit
COAX Uplink
Triggers
RVP8/Rx
SBC
RS232C Antenna Angles
10/100 BaseT LAN Interface
Mouse
Utilities
S 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.
S 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.
Monitor
Keyboard
S 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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RVP8 Configuration Example: High Performance Klystron
IF Signal
Reference Clock
IF Tx Waveform
Pulse width
Triggers
Parallel or Synchro AZ
Parallell or Synchro EL
IFD
14-Bit
COAX Uplink
Fiber Downlink
Digitally Synthesized COHO
Connector Panel
10/100/1000 Base T
Mouse
Utilities
Monitor
Keyboard
IF Tx Waveform
Introduction and Specifications
RVP8/Rx
RVP8/Tx
I/OĆ62
SBC
S 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.
S 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 SoftPlane t 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
DAFCDigital STALO
Horizontal IF Signal
IF Magnetron Burst
Synch Clock
Vertical IF Signal
Polarization Control
Pulse Width Control
Triggers
Parallel or Synchro AZ
Parallell or Synchro EL
IFD
14-Bit
Horz
Fiber Downlink
IFD
14-Bit
Vert
Connector Panel
10/100/1000 BaseT LAN
Mouse
Utilities
Monitor
Keyboard
COAX Uplink
COAX Uplink
Fiber Downlink
RVP8/Rx
RVP8/Rx
I/OĆ62
SBC
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.,
S 10/100–BaseT Ethernet card for additional network I/O (e.g., a backup network).
S RS-232/RS-422 serial cards for serial angles, remote TTY control, etc.
S Sound card to synthesize audio waveforms for wind profiler applications.
S GPS card for time synch.
S 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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1.1.1 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:
S IF video signal.
S A secondary IF video signal, used for dual polarization or very
wide dynamic range applications.
S IF Burst Pulse for magnetron or IF COHO for Klystron.
S 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.
Introduction and Specifications
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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1.1.2 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.
Introduction and Specifications
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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Calibration Plot for RVP8/IFD
Introduction and Specifications
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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Digital IF Band Pass Design Tool
Burst Pulse Alignment Tool
Introduction and Specifications
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.
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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Introduction and Specifications
1.1.3 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 T ypically 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
S
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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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.
Introduction and Specifications
S 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.
S 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.
S 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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