Test, QC & Monitoring Global Viewpoint – December 2019

Portable Test Tools and Live Production

Like a magician setting up a stage for an act, setting up for a live TV production is where all technical challenges are supposed to end. The rest is smoke and mirrors. In live TV, the engineers at the live production are the smoke and mirrors and they do it with test equipment.

Many forms of IP video transport have been adopted in live TV field production, and the benefits begin with the fact that IP is ubiquitous, particularly compared to SDI. That makes IP video much easier to transport because it’s simple network data and the wire much easier to carry and deploy than coax. The risk is that if you rely on someone else’s network for IP transport, your show will rely on an IP infrastructure you don’t control. Who do you trust?

Many production companies prefer to use their own IP networks. Digital video signals such as HDMI, SDI and IP video and all their variants have a unique set of issues different than regular video or data issues. Many digital video issues are related to the physical networks and/or the lengths of the cables. Highly reliable digital TV equipment regularly pushes the limits of physics and technology. Transporting huge amounts of high-speed data across a network in real-time puts cables, connectors, and PHY infrastructures to the test.

The digital cliff is a popular technical term, but live digital TV production people have learned there’s some loose gravel before a signal slips off the cliff. The trick during live production is know where the loose gravel is, and that requires specific test gear. Digital video problems are difficult to troubleshoot with a waveform monitor. The secret to digital live production success is to test in advance, monitor everything live, and use the right test gear.

In addition to checking the common SDI Eye pattern, engineers now must be able to monitor and test ST 2110 workflows.  Being able to – on both the top of the range Qx Series and the handheld Sx TAG. Qx IP now offers SMPTE 2110 support with PTP, with -10, -20, -30 and -40 showing on the stand.

The Phabrix Sx TAG handheld test and measurement tool supports a variety of tests for both SDI and IP systems. The eye pattern shown here  should be familiar to engineers.

The Phabrix Sx TAG handheld test and measurement tool supports a variety of tests for both SDI and IP systems. The eye pattern shown here should be familiar to engineers.

As this industry transitions to IP-centric solutions, important, but less-familiar, tests need to be performed. Enter the SFP+ (enhanced small form-factor pluggable) module. The SFP provides inputs/outputs in an interchangeable form factor. Installed inside an SFP cage hosted by other equipment manufacturers, the modules can be interchanged to provide a different mix of input and output connectivity. Any system test needs to be able to accommodate these signal conversions.

Some T&M equipment provide a variety of interfaces via SFP modules. A variety of optional SFPs are offered for specific uses. This allows the engineer to connect to whatever type of network or signal may be present by simply plugging in a different SFP.  For instance, one SFP might provide 2022-6 IP encapsulation/decapsulation. The SFP can be used for generation, monitoring and analysis of other video formats.

The Eye

Eye and Jitter is an advanced form of physical layer analysis. The Eye Pattern is formed by displaying the clock signal from the SDI data stream then superimposing a delayed version of the clock signal at exactly half way through the duty cycle (or unit interval) of the clock signal. This forms the recognizable eye shape.

The Eye pattern is a tool for the evaluation of the combined effects of channel noise and inter-symbol interference. A good signal looks something like a clean, wide open eye (or eyes). The more open and clear the eye, the less the distortion. Noise increases the peak-to-peak heights and distortions make the eye begin to “close.” Jitter in the eye diagram is represented by the eye’s width.

These are but a fraction of the tests modern T&M equipment can provide. It is important to consider future needs when evaluating new measurement instruments.

In live TV production, the director and camera operators do their best to predict the next shot. During setup, engineers at the production use test gear to set, optimize and assure all source and destination signal qualities. During the live show, the same test gear is used to observe and resolve technical issues to ensure they don’t appear on TV. Digital and IP video don’t often fail, but when it does it’s not a pretty picture.