Applied Technology: Tektronix MPEG test systems

Tektronix MPEG test systems

By Tom Tucker

The worldwide transition to digital broadcasting is truly a massive undertaking. After spending months designing a new installation, the engineer is faced with all the problems implementation can bring, since the whole process of translating a complex system architecture into a working physical reality can be fraught with hidden danger. An engineer may have intermittent signal failure due to a bad connector, or complete signal failure due to an incorrectly configured multiplexer, or any number of other typical installation problems. The only real solution to this conundrum lies in the ability to identify problems generated during the installation process, so the system will continue working into the future.

The Tektronix AD920 MPEG handheld tester provides support for the two main interfaces found in digital broadcast installations worldwide: ASI and SMPTE 310M.

MPEG testers

Tektronix currently offers three test tools to assist in successfully and efficiently installing and maintaining compressed digital video installations. The Tektronix AD920 MPEG handheld tester, AD954 MPEG portable analyzer, and MTX100 MPEG recorder and player help engineers rapidly deploy new equipment – even entire installations – effectively, on time and on budget. They are tools for installation engineers, as well as anyone else tasked with maintaining or implementing an MPEG-2 infrastructure.

The Tektronix AD920 has been designed to provide support for the two main interfaces found in digital broadcast installations worldwide: ASI and SMPTE 310M. Both use BNC connections and run at 270 Mbits/s (ASI) and 19.34 Mbits/s (SMPTE 310M). The output signal level is 800mVp-p±10% (into 75 V) in both cases due to the active loop-through.

The MPEG-2 test device addresses MPEG-2-based systems including DVB and ATSC. It has been designed specifically for confidence-testing applications. For instance, it addresses tests designed to ensure that an MPEG-2 transport stream can be decoded. This means testing against the DVB-defined “TR101 290” first priority test conditions (excluding PID error). It will also enable testing of the physical layer signal.

All of the measurements are displayed on a single graphical display. Clock rate, signal level, transport rate and data rate are displayed as moving bars with an accurate numerical measurement alongside them. This gives instant visual identification of the amount of data carried by the transport stream against the overall bit rate. This helps determine if a transport stream is carrying only stuffing data rather than valid video, audio or data – even if it seems to be correctly structured. Conditional tests, such as sync byte error and continuity count error, are either true or false, depending upon whether or not they comply with the TR101 290 guidelines. The tester also allows the operator to set user-configurable alarms, allowing him or her to continue working on other tasks while still being alerted to ongoing intermittent problems.

A key distinguishing feature is the system’s portability. Battery-powered, it weighs less than 1 kg. Its handheld shape lends itself to crawling around the back of racks, and checking cables in the floor, walls and ceiling. It also provides stream ID functionality, enabling isolation of a given feed from a bank of cables awaiting connection.

Complex analysis

For more complex analysis, Tektronix offers the AD954 MPEG portable analyzer, which provides a more detailed breakdown of the MPEG-2 transport stream. In addition to providing all of the conditional functions of the AD920, this tool also includes stream structure analysis, private data monitoring, and TR101 290 stream analysis for priority 1, 2 and 3, as well as other conformance measurements.

It can be hooked up to a laptop for field work, allowing the engineer to analyze a stream in real time to TR101 290 priority 1, and to interrogate a stream offline to priority levels 1, 2 and 3. The user can also trigger the unit to capture errors, including a pre-trigger buffer if required, or sample streams for further testing offline or at a later date. Additionally, the system allows the user to analyze system information (SI) and program-specific information (PSI) tables on the laptop display.

When used in real-time test scenarios, the analyzer will maintain a log of TR101 290 priority 1 and SI scripting errors as they occur, detailing time and date for later comparison, or store as a record for ongoing system maintenance.

The tester is suitable for connection to ASI, SMPTE 310M and DVB SPI. It does not require connection to a laptop when left to capture a transport stream error, which is helpful in solving intermittent problems.

Another necessary ingredient for installing video networks is a reliable signal source. The MTX100 recorder and player allows the user to play, record and stress a design to ensure that even under the harshest operating conditions, no fault will occur. It is light, compact and portable. It offers users many interface options, including ASI, DHEI and DVB Parallel. It will play out at data rates up to 200 Mbits/s while offering seamless looping and PCR jitter insertion to test stability. Another key feature is its transport stream structure view, which allows rapid identification of the overall stream structure even before playout.

The rollout of digital video services has created a rapidly growing need for easy-to-use installation and maintenance measurement tools designed specifically for digital video applications. Whether an engineer needs a go/no-go solution or needs to provide a full analysis and characterization of a system’s entire health, a test and measurement system from Tektronix can fulfill this need.

Tom Tucker is a marketing manager for the Americas for Tektronix.

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