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Digital data recording: a battle of standards

Dependency upon digital data recording is widespread. The world's leading navies require it for reliably recording and storing, for long periods, the huge amounts of digital sonar data required to build up acoustic databases crucial for anti-submarine warfare (ASW). Air forces need it to record and reproduce the electro-optic and infrared imagery captured by the latest generation of advanced airborne reconnaissance sensors. Flight test centers use digital data recording to capture critical data when there is often only one chance to secure the necessary information. Intelligence operators worldwide require it to write down and analyze the reams of electromagnetically emitted data intercepted by super-sensitive and super-secret signals intelligence equipment.

High performance digital data recording is a specialized niche market with few players. The equipment is described by an industry official as "the worst mix of mechanics and electronics to get right, particularly if you want to build machines that work in harsh environments."

Since the recording of digital data became a major requirement a decade ago, the data recorder market (specifically at the high-end) has been characterized by a battle of standards, followed by the changes of ownership, mergers, or even the withdrawal, of several companies.

At the beginning of this decade, it appeared that a US Department of Defense-sponsored military standard (MIL-STD-2179A) would be the one most frequently applied for digital data recording. Three major industry players - the then Kodak-owned Datatape and Metrum Information Storage in the US, plus Schlumberger Industries of France - had adopted this 19mm helical scan data format standard and had logged orders for various defense applications. For example, Colorado-based Metrum had won three key towed array sonar programs: the USENavy's (USN's) Trident Sonar Processing and Recording System (TSPARS - procured through Johns Hopkins University Applied Physics Laboratory); the Canadian Towed Array Sonar System (CANTASS); and the Royal Netherlands Navy's (RNLN's) Anaconda program.

Competing recorders

A fourth company (Ampex Data Systems in the US) was sticking to its own 107Mbits/s DCRsi (Digital Cassette Recorder system incremental) standard using transverse scan recording of one-inch data tracks on one-inch (25.4mm) wide tape. In 1990, Ampex claimed it had established a de facto standard with about 450 machines sold.

In the early 1990s, MIL-STD-2179A was rapidly outmaneuvered by the related ID-1 standard for high performance digital data recording and storage, set by the American National Standards Insti- tute (ANSI) and registered as ANSI X3.175-1990.

The ID-1 standard, like MIL-STD-2179, uses regular 19mm D-1 magnetic tape cassettes but it has several significant differences. The most important of these is that while MIL-STD-2179A specifies the recorder heads to be at a 90 angle with respect to the direction of the track on tape, in ID-1 the heads put data tracks on the tape from alternating azimuth angles of 15. This has proven to be advantageous in harsh environments of extreme temperatures, high vibration, g forces and humidity that can be found in defense applications in operational platforms like fighter aircraft reconnaissance pods.

Despite the fact that there is a 5m wide guardband between the 40m wide data tracks on a MIL-STD-2179A recording, high vibration levels and other environmental influences can cause the tape to flutter when going past the heads, leading to mistracking during playback. In ID-1, guardbands between adjacent tracks are unnecessary since a head of one azimuth orientation is unable to read an adjacent track laid down in the other.

The technical difficulties experienced by the MIL-STD-2179 community, understood to be associated mainly with achieving reliable data interchange under adverse operating conditions, led to the situation being reduced to "something approaching chaos," according to one industry source.

Metrum had to abandon the MIL-STD-2179 market. Its TSPARS contract was taken over by Schlumberger supplying DVE6000 series (12 DVE6220s on board the submarines and DVE6420s for playback and analysis ashore) equipment. The Canadian Forces Maritime Command turned to Sony's DIR-1000 ID-1 recorder. In June 1992, the RNLN (followed by the Pakistan Navy two years later for its TypeE21 frigate active towed array sonar) selected non-standard micro-track Pegasus recorders from UK firm Penny & Giles Data Systems. In the Dutch case, the Pegasus recorder was chosen over a competing DCRsi offer by Ampex.

These developments were clearly less than satisfactory from the stand-point of interoperability (the original driving force behind the establishment of MIL-STD-2179A). CANTASS and Anaconda, although supposedly having to work alongside each other in NATO anti- submarine warfare, are now totally incompatible with each other in terms of tape crossplay.

The confusion was further com-pounded by the introduction of MIL-STD-2179B which included some but not all of the features of ID-1. Effectively, there were three incompatible standards for 19mm helical scan recordings: 2179A, 2179B and ID-1.

Datatape, which had been selected for the US Advanced Tactical Air Reconnaissance System (ATARS) program, had already opted for the ID-1 standard, but the cancellation of the original ATARS program led to its A-120 recorders being shelved as well.

There are currently two major standards in the market for high-performance (above 64Mbits/s): ID-1 versus DCRsi. The latter uses transverse scan recording. According to information provided by Ampex, this derives its name from the fact that the scanner spins at 90 to the direction of the tape motion, describing a series of transverse stripes in the form of a raster as the medium (the magnetic tape) passes. With head speed being high in respect to tape speed (2,550in/s against 5.3in/s), each swipe is almost perpendicular to the direction of tape movement (89.88) and less than one-inch in length. The 107Mbits/s version of the DCRsi recorder uses six individual recording heads arranged at 60 intervals around the scanning drum, each with a track width of approximately 0.002in (0.051mm).

Hostile applications

The use of short, straight and relatively wide tracks has been shown to give a high degree of immunity to the effects of mechanical shock and vibration, changes of temperature and high humidity. According to Ampex, this makes the system intrinsically well-suited to hostile environment applications. Additional protection is offered by azimuth recording (as in ID-1) in which stripes are recorded with alternating positive and negative azimuth.

Ampex has reinforced its claim of having set a de facto data recording standard, with more than 1,500 of its machines in service worldwide in fighter and passenger aircraft, helicopters, surface ships, submarines, military vehicles, and their supporting ground-based facilities. The standard DCRsi tape cartridge stores 400 Gbits (50GB) and all models in the DCRsi range are said to be fully crossplay compatible.

Three rugged variants are offered:

A DCRsi 480 version (capable of 480 Mbits/s) is expected to be marketed later this year. However, an important recent addition to the rugged DCRsi range for airborne tactical reconnaissance applications is the DCRsi Clip-On unit which adds a 1Gbit/s snapshot imaging capability by increasing the thoughput to that level. Its baseline solid state storage capacity is 5Gbytes although larger memory drives can be specified. The unit is designed principally to be used with a DCRsi 240R cartridge recorder in an airborne image-gathering role. Data acquired at 240 Mbits/s or lower is stored in cache and on tape simultaneously. Higher rate data streams are initially cached and then automatically backed up to tape when the memory is nearly full, or on a command from the operator.

DCRsiE120 and DCRsiE240 are also available in bench and rack-mounted configurations. Major DCRsi defense applications include the US Air National Guard F-16C/D reconnaissance pod first flown by the Virginia ANG over Bosnia during 1996; the USN's F/A-18E/F Super Hornet flight test program; and the UK Royal Navy Merlin ASW helicopter for which Ampex (teamed with Normalair Garrett) is supplying 50 recorders under a 1994 contract.

The Ampex recorder family has flown on a wide variety of tactical and strategic platforms. The former category includes RF-4C, F-14, F-15, F-16, F/A-18, F-111, A-10A, F-117 and F-22 aircraft. Strategic platforms on which the Ampex recorder family have been deployed include SR-71, U-2, AWACS (Airborne Warning and Control System), Joint STARS, (Joint Surveillance & Target Attack Radar System), Boeing 767, P-3C, RC-135, B-1 and B-2 aircraft.

In the case of ID-1 and MIL-STD-2179, helical scan recording is used. This differs from transverse recording primarily in that the scanner is angled so that each head describes a long helix across the tape rather than a short transverse swipe; the angle of the helix being about 5 to the edge of the tape.

Sales pedigree

The main players offering ID-1 products are Paris-based Enertec (the former Schlumberger Industries which since late last year is owned by UK-based Avicore Group alongside airborne reconnaissance manufacturer W. Vinten); Sony Broadcast & Professional; and the US company Metrum-Datatape which has resulted from a 1997 takeover of Datatape by its former competitor Metrum.

Market leader Enertec has managed to overcome the initial MIL-STD-2179 problems and now offers the DV 6000 series machines both for 2179 and ID-1 applications. Enertec has built up an impressive pedigree of DVE6000 sales, particularly in the market for harsh environment machines in which the company is the only real competitor against Ampex's ruggedized DCRsi machines. In airborne reconnaissance, Enertec has sold 19in (48.26cm) rack-mounted DVE6000 systems for a range of imagery processing systems in the US, including the Raytheon E-Systems Joint Services Image Processing System (JSIPS). Compact, ruggedized machines have been sold to the new ATARS program for the US Marine Corps (64 recorders now being delivered with more to follow if the USN also orders ATARS). The UK Royal Air Force (RAF) has selected DV 6000s for its RAPTOR Tornado stand-off reconnaissance program of eight pods and two ground stations. The electro-optic/infrared (EO/IR) imagery produced by the Hughes-built RAPTOR sensors is described by RAF sources as "enabling us to read vehicle license plates from an altitude of 26,000ft and a distance of 30nm," but the system is highly reliant on the recorders to allow detailed post-mission analysis.

Other DVE6000 applications include the new Thomson-CSF Optronique TEORS/DESIRE reconnaissance system prototype for the MirageEF1CR, while Enertec is planning to compete against Ampex for the upcoming Danish, Dutch and Swedish reconnaissance pod programs for the F-16A/B (Mid Life Update) and JASE39 Gripen.

Enertec has supplied DVE6000s to two US surveillance/intelligence applications (one shelter-mounted, the other in a laboratory environment), while the French SARIGUEENG new-generation strategic SIGINT (signals intelligence) DC-8 platform (see IDR 12/1997, pp28-35) will also use the type. In the ASW market, Enertec has supplied large numbers of DVE6000 recorders to programs in France. This includes Sonar Nouvelle Generation - SNG on board the Le Triomphant-class SSBNs (nuclear-powered ballistic missile submarines)and the SLASM (Systeme de Lutte Anti-Sous Marine) active towed array sonar system on board destroyers. Enertec has supplied the Scylla sonar suite in Australian Collins-class submarines and the above-mentioned TSPARS program in the US. In the UK, DVE6000s have been selected for SonarE2076 (15 recorders for the new fleetwide SSN suite) and the Nimrod 2000 maritime patrol aircraft. The Sonar 2087 (TypeE23 frigates) and Sonar 2054 (SSBNs) programs are also being targeted, as is the RAF's ASTOR (Airborne Stand-Off Radar) airborne ground surveillance program which is expected to incorporate an advanced EO/IR imaging sensor in addition to the planned synthetic aperture/moving target indicator (SAR/MTI) radar.

In addition, DV 6000s have been used in system and flight testing activities in support of the Thomson-CSF RBE2 radar, the UK-French CLARA (Compact Laser Radar) obstacle warning system, the Thomson-CSF SPECTRA and SERVAL countermeasures systems, the Aerospatiale Polypheme missile, and on the French MoD's test ship Monge and the CEV test range Cazaux.

The DV 6000 range is available in various types. The current top model and the first with eight heads is the ruggedized very high data rate cassette recorder DVE6821 which, based on the combined operation of eight data channels, offers a (buffered) data rate capability of up to 520Mbits/s, record and playback. It is designed for use on board surveillance aircraft, mobile shelters, submarines, surface ships and ground stations. Its non-ruggedized version is the DVE6831.

Other variants include the DVE6421 (the French Navy SLASM-2 ASW suite and the UK Trafalgar-class SSN) and the DVE6450 (ATARS airborne recorder). The last type number is the odd one out of Enertec's designation system for the DV 6000 series, in which the second digit signifies the number of heads. The third digit denotes whether it is a compact ruggedized ('1'), a standard ruggedized ('2') or a laboratory ('3') machine. The fourth digit signifies whether it is a MIL-STD-2179 ('0') or ID-1 standard ('1') machine.

Sony is offering its DIR-1000 series of recorders on the ID-1 market. The latest model, the DIR-1000H, provides a maximum rate of 512MBits/s, the fastest data rate within the series. As highlighted above, one defense application of the DIR-1000 series is the Canadian Patrol Frigate (CPF) program in which Sony's DIR-1000L recorders are an integrated part of the CANTASS data flow and conversion architecture used for acoustic and mission analysis. DIR-1000 series recorders are employed in Germany on board the TypeE750 research ship FGS Planet for towed array sonar experiments by the FWG. In the UK, the Centre for Defence Analysis at DRA (Defence Research Agency) Farnborough is using DIR-1000s for research and development work.

Metrum-Datatape, a subsidiary of Group Financial Partners, includes the Government Systems Division of Datatape Incorporated and offers the full line of Datatape products under the new Metrum-Datatape label. In addition, the Metrum Division of Bell Technologies, another subsidiary of Group Financial Partners, will operate jointly with the former Datatape Government Systems Division under the Metrum-Datatape name. This newly created business has an extensive offering of high-speed digital and analog products using both rotary and longitudinal technologies.

Its ID-1 products are in use with the US and other intelligence communities. They include the DCTR-LP series which provides digital data recording capabilities from 25Mbits/s to 400Mbits/s (depending on the configuration chosen.) The DCTR-LP200 allows for a record range from 25 to 200Mbits/s with the DCTR-LP400 covering the range from 50 to 400Mbits/s. Designed in a standard 19in (48.26cm) rack-mount configuration, the DCTR-LP Series is aimed at applications in laboratory environments. Each unit has an optional active front panel display, providing ease of operation through a series of menus and program options.

Data integrity is engineered directly into the DCTR-LP Series with each model offering a bit-error rate of less than one in 1,010. Additionally, these units use commercially available 19mm cassettes in either small, medium or large size. For space restricted, rough-ride environments a rugged HDDR (head-down display radar) version is also available.

A number of companies offer a range of products operating at lower data rates, again with various standards including Super VHS (S-VHS), DAT (Digital Audio Tape), DTF (Digital Tape Format) and Digital Linear Tape (DLT). According to some senior industry sources, tape format standards are less of a concern than interface standards.

"Data must be received by the recorder in line with the various standard data buses that are being used. Data transfer standards are also important and these are all becoming oriented towards defined but flexible packet data formats. In this, the IRIG group is still at the forefront of setting such standards. We must, however, be very careful that standardization for its own sake does not prevent the user getting access to the latest technology and other data handling developments that provide ever greater data densities, capacities and reliability," said Dr David Nutton, director of the UK-German company Racal-Heim.

According to Nutton, Racal-Heim wants to offer the user a comprehensive catalog of interfaces that will minimize the other equipment required on board a defense platform (aircraft, ship, or fighting vehicle).

Racal-Heim has the following product range:

Sony intends to pursue adoption of the cassette-based, half-inch magnetic tape DTF-1 standard for helical scan recording as an international standard through application to the International Standards Organization (ISO). DTF drives are based on Digital Betacam technology, claimed by Sony to be the de facto video recording standard for high-end professional broadcasting with over 350,000 Betacam VTRs currently in operation around the world.

Metrum-Datatape offers the Model 64 (up to 64Mbits/s), the rugged Buffered VLDS (up to 32Mbits/s) and the Model 32HE (up to 32Mbits/s 160Mbits/s at burst rates) variable speed digital data recorders. The Model 32HE is particularly well specified for hostile environment applications. All three are based on the IRIG standard for half-inch tape using broadcast-quality S-VHS tape. They can be linked with the Metrum-Datatape ARMOR multiplexer unit to form an integrated system for digital and analog recording. The company's MARS-II airborne recorder series are capable of data rates up to 40Mbits/s.

At the recent International Telemetering Conference in Las Vegas, Nevada, Avalon Electronics of the UK launched a new series of high capacity data recorders based on DLT (Digital Linear Tape) cassette technology. Already a major supplier of helical scan S-VHS cassette recorders for analog and digital data capture in aerospace, defense and intelligence applications, the company is one of the first to adapt the DLT system for use in aerospace, intelligence gathering, and high speed data communications applications.

Developed as a low cost mass storage peripheral for PCs and workstations, the multi-track DLT linear format offers a number of important advantages over S-VHS for real-time data capture. Sustained data transfer rates between zero and either 12 or 40Mbits/s can be recorded and reproduced. The highest data rate available on Avalon's current S-VHS range is 8Mbits/s. DLT cassettes also store more data: 280Gbits (35GB) of formatted data compared to the 86Gbit (10.8GB) of a typical S-VHS cassette.

Initially, Avalon will offer a family of five digital recorders based on the 12Mbits/s and 40Mbits/s drives. Designated Series AE6100HW the new range will record between one and eight separate serial bit streams in NRZ TTL, ECL or MIL-STD-1553 format with error rates better than one in 10 (14). Data can be output either in the same format as it was recorded or via an optional SCSI-2 replay interface for immediate computer analysis.

The system architecture allows a number of recorders to operate in parallel without the need for sophisticated resynchronization techniques. For example, five 40Mbits/s units can operate logically as a single, inexpensive 200Mbits/s data acquisition system.

The new DLT-based systems, including record and replay electronics, power supplies and environmental control measure 176x220x500mm, allow two units to be installed side by side in a standard 19in rack. For the future, Avalon is planning a range of multi-channel analog/digital front-ends allowing users of ageing, open-reel IRIG recorders an easy and low risk migration path to the new DLT technology.

Many in the data recorder industry agree that for the next decade or so magnetic tape will continue to be the most cost-effective medium for digital data recording, despite the advent of hard disk and solid state technologies (as heralded by US companies OSC/Fairchild Defense and Odetics, which have been marketing high-speed solid-state recorders for harsh environment applications).

According to Nutton: "Recent tape developments such as DLT are all showing a great increase in data rate and capacity which is continuing to outstrip the developments in solid state (both in terms of capacity and price). For some applications, magnetic discs are attractive for their access time but are not practical for archival, while solid state is similarly unsuitable for an archive medium.

"Optical disks are again suitable for some applications but suffer from susceptibility to shock and vibration during recording and a relatively low data recording rate. Today's trends are therefore to offer increased choice to the customer so that he can make his own optimization depending on his exact application. He can even have multiple versions of the same equipment to give common interfacing but optimized media."

Driving data investment

At Enertec, director for navy and intelligence programs Jean- Francois Sulzer says that for data recording, costly investments will have to be made if tape drives are to keep up with hard disk or solid state developments.

"In the past, the broadcast and consumer industries have funded research and development in this field but in recent years this has slowed down because their needs are limited to data rates of around 300Mbits/s. Hard disk technology, however, fueled by the computer industry, has improved the fastest over the last five years," he said. "By putting in more heads we can push the data rates up to around 500Mbits/s but it's pushing existing technology, not being innovative."

However, for data storage cost will be the decisive issue. At US$1 per gigabyte, D-1 and the newer D-5 tape cassettes will be far less expensive than hard disks, which cost a ratio of 100 more. They will certainly be cheaper than solid state, which "probably is another 100 times as expensive. It's a big cost impact if you lose a solid state data recorder cartridge somewhere in the logistic chain; if you lose a D-1 cassette it's nothing," Sulzer said. He added that Enertec's view is that the different technologies will co-exist, with solid-state capacity being used as buffer to support tape-drives. "It's the throughput rate you have to keep in mind, not just data storage density and cost. A high-speed helical scan recorder like our DV 6000 still is faster than a hard disk. That is probably also what prevented optical disks from getting into this market. They are just too slow."

The general confidence in the future of magnetic tape is highlighted by the recent establishment of Electro-Mechanical Designs (EMD) in Hastings, England, which designs tape transport systems. According to company founder Chris Duckling, EMD is unusual in that it has the ability to design and build tape transports or customize an existing one. "This is a skill that has largely disappeared from the Western world, yet there continues to be a need," Duckling said.