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HDTV Encoding Rack Design

1 May, 2002 (17:00) | DTV, HDTV, Projects

Here is a project I am justifiably proud of. Our corporate engineering management had determined that we were to use a Harris Flexicoder as the core of our HDTV encoding, but outside of that we were to determine what we needed to best integrate it into our facility. Initially, I was not pleased with the choice in encoders as I had seen better performance from the Harmonic encoding systems. However, after getting my hands on more thorough documentation and working with the encoder package that included an integrated ‘Master Control’ module I quickly began to see the potential for the system. I added to our DTV budget, not just the elements needed to encode our studio signal digitally and pass through the network HD signal, but also to monitor and perform simple localized troubleshooting of problems we may (and probably would) encounter in the future.

Simple and effective HD encoding rack.This single rack encoded the studio signal for both KHBS and KHOG. In order for the correct TSID to be present in the bitstream destined for KHOG, the use of Triveni’s StreamBridge product was needed and worked quite well.

Originally I designed the system to allow the HD signal from the network to be switched to the transmitters based on a schedule programmed into a timed controller. However, this required weekly updating and last minute changes if the network changed it’s HD schedule (and they were prone to do so). If I had to do over I would have used a simple toggle-switch to allow the master control operator the ability to select when the HD signal is switched to the transmitters, which had been done at other stations.

The Ikegami monitor with it’s multiple video format card slots allowed us to view the video signal in real time at various stages in the encoding process. This way we could see what was happening to our signal in native NTSC at the studio, after decoding to SDI (601), after conversion to HD SDI (SMPTE-292) and after decoding from the receiver into component NTSC.

What is not shown are the items of test equipment I purchased and used along with the encoding rack. At the transmitter we kept the Tektronix RFA-300A, but at each studio I purchased a Sencore AT-985 (unfortunately no longer available), a Sencore TMS-1780 which is a fantastic HDTV / PSIP bitstream analyzer and a capable 8-VSB analyzer all rolled into one and an Agilent spectrum analyzer. In my humble opinion these are the absolute basic necessities and I knew if I didn’t purchase them at the time of the DTV build out I would have an extremely difficult time doing so later on when we were in a normal maintenance capital cycle.

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