Getting the ISH in Sync
With all the talk about the information superhighway, the ability to route and distribute high resolution video signals is becoming more critical every day. Designers have to be sensitive to the methodology of transmission, sync rates, regeneration issues and sync timing with respect to the transmission type.

When General Projection was hired by the U.S. Army (through their Prime Contractor, E-Systems of Dallas, Texas ) to build the Army’s largest AV system (for the Strategic Wargame Facility at the U.S. Army War College Carlisle, PA), one of the primary concerns was that all interior signal routing be fiber optically based. This presented a challenge in that a multitude of sources from VHS VCR’s to Sun workstations and all resolutions in between had to be automatically supported.

The 155,000 square foot building features state-of-the-art communications, video, and computer systems. There are 40 reconfigurable wargaming, seminar or meeting rooms. These rooms, the Main Conference Room, and other areas can host 500 person excercises or other activities.

The Installation
General Projection provided and installed a very large fiber optic transmission system based on Meret Optical products. Soon it was discovered that the disparate scan rates, bandwidths and, most importantly, sync timing differences could easily bring the system “to its knees.”

After much collaboration with E-Systems, the design consultant at T-ASA (Television-Audio Support Activity) and the manufacturers involved (including Meret, Pesa, General Parametrics, Extron, Mitsubishi and General Electric), General Projection engineers determined that the method of synchronization “regeneration” of the fiber system was providing minute timing differences that would cause display and source devices to be mismatched. This was quite a surprise in today’s world of “multi-scan” and “auto-lock”, both overused terms that become lost when so many devices are trying to share a common distribution methodology.

The Challenges
The specifics of the problems that developed are: Display devices by Mitsubishi (XC3725C) and GE (Imager series) were not provided vertical “front porch” sync timing that matched the specifications of the devices. Thus the devices had difficulty “locking” onto the sync signal and when they did the picture quality was quite poor or the wrong memory location was looked-up by the device. Further, when adjustments to local Extron computer interfaces were made that sufficiently changed the front and back porch signals, the next type of signal routed would be out of specification. The engineering done on site to correct the problem proved that the regeneration of sync, typical of high resolution fiber optic transmission equipment, was the ultimate source of the slight mismatches.

The Answer
The solution finally reached was to insert additional Extron conditioning equipment (in this case a modified the PA-1-200. Extron has since permanently incorporated this modification into this product.) to make minor changes to the vertical sync front and back porches which then allowed the fiber optic system to regenerate a sync signal within the specifications of the source an display devices.

As fiber optic costs continue to drop and the value of that method of transmission is further realized, more and more designers will want to use fiber as the primary method of signal movement. Fiber eliminated ground loop potential, electrostatic noise inducement and typical coaxial loss budgets. While not the solution to every environment, any high resolution cable run in excess of 500 feet or so as well as very run between buildings, underground or through high electronic noise environments should be considered for fiber transmission.

Costs per signal group (say for a single path of RGBS at 100 Mhz bandwidth capability) now can be as little as $2,000 plus cabling. With the quality and other benefits mentioned, this is becoming viable for virtually any size system. In major projects such as the Strategic Wargame Facility, it is impractical to choose any other method. However, with little or no standardization of the more mundane aspects of synchronization, the engineering challenges can only continue to grow. The day to day demands of the nation’s information networks demonstrate again the need for design firms to provide the capability to deal with such problems in advance of the installation. This presents another excellent growth opportunity for our friends in the design community.

The addition of sync conditioning equipment will be critical in any environment where fiber optics and the issues of signal regeneration become concerns. Minute adjustments (usually with an oscilloscope in hand) will be necessary to bring the diversity of frequencies and sync types into line with the requirements of the sources and ultimate signal destinations. Contact or Email Solutions at 407-260-5511 for more information and circuitry suggestions.