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Tuesday, November 13, 2007

Spotlight Feature: How WKYC Transmits Over the Air

Ever wonder how our television pictures gets from the WKYC Digital Broadcast Center's control room to your tv set? The whole process starts with our over the air signal for those of you without cable or satellite (those services are fed directly via fiber links to the individual companies).

We asked WKYC Transmitter Engineer Dave Kushman to give us a tour of the transmitter facility in Parma & explain how it all works. Be sure to check out Dave's website:

The program video and audio from the studio come to the transmitter site in two formats, analog and digital.

The analog video can only carry a limited amount of information. I'm sure you have noticed the lines across the screen. There are 525 of them. At the top of the screen, hidden from view, is an area that contains, closed captioning information, an occasional test signal and precise time information. Each on its own line. The audio has its own processing and path to the aural transmitter. The output of the visual and aural transmitters are then combine just before the RF (radio frequency) leaves the building on its way to the antenna.

Digital on the other hand, can carry much more information. The video and audio are all in one stream along with the above information and much more. While we actually transmit digital on channel 2, information in this stream tells your TV that you are watching channel 3-1 or 3-2. It works the same way with the other stations in town. Since the audio is also digitized, it is embedded into the digital stream, there is no need for a separate aural transmitter.

Programs created in the analog format are also converted to the digital format and both are then sent via fiber optics to the transmitter site.

Should you have an analog and a digital tv tuned to channel 3 at the same time, you would notice there is a slight delay in the digital picture and sound. That's because it takes a certain amount of time to convert analog into digital signals. At the transmitter site, the analog and digital signals have their own processing equipment and are then sent to the individual transmitters.
Besides having a diesel generator to run the entire transmitter site should there be a power failure, the program from the studio can either be fed to the transmitter site via a terrestrial microwave path, or satellite if need be.

Our channel 3 analog transmitter operates at about 25 thousand watts and the digital channel 2 about 5 thousand. Since digital signals travel farther for a given power, there is no need to run that transmitter at the same level as the analog.

The antenna style that we use is called a Batwing. At the antenna the analog power is in effect multiplied to a little under 100 thousand watts. The technical term is Effective Radiated Power (ERP).

The digital power is only raised to about 8 thousand to cover the same area.

Check out our slide show of our transmitter location. Special thanks to Dave Kushman and Dawn Ermler-Fischer for helping us take the digital pictures.


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Blogger W8MAQ said...

Thanks for the slide tour of your transmitter plant! You have a backup antenna, do you have a backup transmitter as well? Regards...

9:29 PM, January 01, 2009  

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