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Apparatus and Method for Effecting Data Transfer Between Data Systems

The National Aeronautics and Space Administration (NASA) seeks qualified companies for commercialization of the redundant fiber-optic transceivers that have been incorporated into the High Speed Data Acquisition System (HSDAS) at Stennis Space Center to communicate the high speed rocket engine test data from the test stands to the data acquisition facility. These and similar transceivers could also prove useful in other situations in which there are requirements for acquiring data at safe distances from instrumentation located in hostile or potentially dangerous environments.

Potential Applications
The Fiber-Optic Transceiver can be used in any application where sensor data need to be transmitted over long distances.

• Propulsion system testing
• Nuclear power plant operations
• Gas detection
• Defense systems

The Technology
Duplex data communications at the Stennis test stands typically take place using the Racal Storeplex system, which connects the signal processing unit (SPU) and the tape transport unit (TTU) by coaxial cable. This cable, however, can experience data transmission problems if it is longer than 50m.

Using two transceivers allows the SPU and TTU to be connected by a fiber optic data link. Short coaxial cables connect one transceiver to the SPU and one to the TTU. The two transceivers are connected by a fiber optic link that can extend up to 25 km long. The transceiver features a 125 Mbps card), and single mode or multimode optical inter face. As a stand-alone transceiver with built-in power supplies, it uses laser diode transmitter modules and integrated receivers for the optical interface. Two transmitters and two receivers are used at each end of the link with automatic or manual switchover to maximize communications reliability.

With these transceivers, the analog instrumentation outputs are digitized and preprocessed on the test stand and then record remotely on a commercially available high speed data recorder. The electrical output of the recorder - a modified TAXI (Transparent Asynchronous Transmit/Receive Interface) signal containing a stream of digital data at a rate of 125Mb/s - is fed through a standard duplex coaxial interface to the first of two fiber-optic transceivers. In the first transceiver, the electrical signal is converted to an optical signal which is then transmitted over one of two duplex fiber-optic links to a second transceiver located in the data acquisition facility a safe location from the test stand. The fiber-optic link can be as long as 25 km - much longer than the coaxial cable. In the second transceiver, the optical signal is converted back to the original electrical signal and this data is then stored on the high-speed data recorder.

Each transceiver contains two fiber-optic transmitters and two fiber-optic receivers. Under either manual or automatic control, electronic switching circuitry in the transceivers selects the transmitter/receiver pair that generates the best received signal. The redundancy of transmitters and receivers also helps to prevent communication errors that could arise form defects in the fiber-optic links.

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