For years, the mainstay tools of television engineers in stations and facilities all around the country have been the trusty waveform monitor and vectorscope. Throughout studios, edit rooms, engineering facilities and broadcast centers, TV stations large and small, as well as broadcast and cable networks, are replete with these workhorse test and monitoring instruments. And, for simple go/no-go testing, there is the ubiquitous video monitor. Tap virtually anywhere into that NTSC video signal path and either video or a blank screen appears, quickly telling you whether there is a signal or not and what the content of that signal looks like visually.
In the early days of television, Tektronix — then a nascent manufacturer of oscilloscopes for general test and measuring applications — introduced a version of one of its scopes, the 524AD. According to the operating manual, it was “specifically designed for maintenance and adjustment of television transmitters and studio equipment.” This was one of the first such instruments dedicated to television signal measurement and analysis using visual display parameters. Next were dedicated full-rack-width waveform monitors and vectorscopes, followed by the half-rack displays that have been so prevalent over the past several decades and ultimately evolving into today's multifunction single unit displays.
In analog television, broadcasters have long been concerned about sync and burst measurements, white level and black level settings, differential phase and gain . . . the list could go on and on. As analog goes dark, we face a new glossary of terms and a new set of monitoring and measurement concerns. The relatively easy to view and measure analog signal is now being replaced by an SDI signal that is being compressed and encapsulated into a transport stream (TS). That TS carries multiplexed, packetized data representing one or more programs and services and is then 8-VSB modulated to carry it to off-air DTV receivers.
Enter the new lexicon. With a new set of critical concerns — bit error rate (BER), modulation error ratio (MER), program clock reference (PCR) drift and jitter, and Program and System Information Protocol (PSIP) table errors — waveform monitor and vectorscopes designed during the 8-track era cannot quite cut it in a digital world.
But, your friendly purveyor of test instruments can come to the rescue. Welcome to the world of MPEG monitors and analyzers. In the digital world, test and measuring is important. Forget the graceful degradation of analog signals slowly sinking into noise and distortion, and welcome to the cliff effect. In our digital world, the video is either there or not there. If it is there, it is either pristine or pixelized. Have excessive PCR jitter? Get ready for the “why is my screen blank?” phone calls. There are a myriad of problems that can cause that viewer screen to go blank. Need a refresher on MPEG measurements? You can find helpful articles on the Broadcast Engineering Web site. And, don't overlook that heretofore mentioned friendly test equipment purveyor. I'm sure he would be happy to provide an MPEG test and measurement primer during the course of demonstrating that box he wants to sell to you.
Remember that infamous technician who thought he was having a private viewing of a porn film? That TS is capable of carrying multiple services; better know what's in it. It's almost February. What's in your transport stream?
Anthony R. Gargano is a consultant and former industry executive.
Send questions and comments to:anthony.gargano@penton.com
