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New Applications in HoW HDTV Video Distribution
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hings are finally coming together for large and small church media systems. On the audio side, the cost of quality digital audio mixing and snakes has come down so far that just about any site can afford to upgrade. On the video side, new multi-channel switcher/scalers are adding new features and lower price levels for seamless crossfades and HD-SDI video production. At the same time, new solutions in HDTV RF technology have dramatically reduced the costs of facility-wide HD video distribution. A few years ago, creating an in-house HD channel would require several components costing up to $40,000. Today, one HDTV modulator can do the job for less than $1,500 a channel. There are many reasons HDTV RF is gaining in popularity as a distribution network. First, RF is easy to install and operates on national standards. No proprietary interfaces are needed, any TV can tune in. RF is scalable in all dimensions - add new sources at any time, January 2012
by Doug Engstrom
freely connect any number of TVs, and you can easily branch existing coax runs to extend the network. You don’t have to use digital channels for everything, you can mix in analog channels as well. If you have existing RF coax wiring, all your wire and components are fully compatible with digital HD channels. The attractive cost/performance ratio of HDTV RF distribution is spurring three key applications in houses of worship: • Distribute digital signage facility-wide • Broadcast live High Definition video as HDTV channels • Incorporate channels from off-air and satellite/cable TV sources
RF Components There are a few basic components to an RF system. • HDTV Modulator. This unit receives video in the form of HD Analog Component, VGA, HD or SD SDI, or Composite video, generally with options for digital or analog audio, then converts the media to an MPEG2 video stream. tfwm.com
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Video/HDTV Distribution The term “Modulation” refers to the fact that the unit marries the content with a TV frequency, which is then broadcast over the RF system. • HDTV Tuner. A tuner essentially does the same process in reverse, called demodulation - it tunes to the frequency, splits off the MPEG2 stream, then delivers the video and sound to the screen. HDTV tuners are standard feature on consumer and some professional flat panel displays, so a cost effective HDTV
capable television is easy to add or to replace existing NTSC analog televisions when they fail or are at end of life. • Combiner. A Combiner has 2-16+ RF inputs that merges the feed from each modulator into a single RF feed, where each channel is separated by frequency. A 2-way or 4-way splitter is a combiner as well, just use it in reverse. That one feed is then amplified and split to the various TVs in the system.
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Sounds a bit high-tech, but you experience the technology every day using your cell phone. It modulates your voice and data to a radio frequency and sends the signal to a cell tower. Signals to your cell are demodulated so you can listen, look at pictures and read the text.
Distributing Digital Signage Content If you are running a full-bore IP signage system where 1) Every destination is playing different programming or 2) The far-flung destinations can only be reached over IP (actually the cable distances can be a limiting factor here, depending on how robust an IP network is installed in a facility) then Ethernet is your best delivery truck. But if you plan on distributing just a few programs over at single facility then using HDTV over RF is a great way to go. For example, many sites are composing signage in Final Cut Pro, other graphics programs like PowerPoint, Keynote or worship graphics software systems- or simply creating a group of slides that loop, then playing them back on a computer such as a Mac Mini, Apple TV or BluRay player. Other sites may use a more robust digital signage solution, with PIP’s, information crawls, dynamic facility schedules and other varying content. Distributing your signage or video content is fairly simple- you provide an appropriate output signal that your modulator will accept depending on make on model as mentioned before- HD Analog Component, VGA, HD or SD SDI, or Composite video. Then you set up the modulator to broadcast on the appropriate channel, combine the RF outputs of the different modulators with a combiner, then the combined output is then distributed via a network of amplifiers and splitters to the cable drops at each television site. It is important to understand what your entire RF cabling network looks like- how many drops, what the cable distances to each drop are, and how your system might ‘grow’ for additional drops in the future. You January 2012
can have either a simple ‘star’ distribution modelwhere you distribute all cable drops from one point, or a ‘Spoke and Hub’ model- where you have a main location where all the sources would exist, but then you distribute several ‘spokes’ or cables to different locations in your campus, where you then have ‘hubs’ where multiple cable drops are used to feed the channels to the end televisions. Obtaining the help of a qualified expert could be of extreme importance if your system is complex or includes more than eight receiving televisions.
HD-SDI Broadcasting HDTV channels over RF are a great way to send High Definition content across the facility. HD-SDI and other high definition signals are great for in-sanctuary video production and display, but sometimes can be limiting for long-distance viewing depending on the infrastructure you use- copper or fiber. If you have a High Definition switcher, my preference is to stay in native output format of the switcher to the insanctuary projectors/displays. If you are using HD-SDI there are low-cost converters that can mate HD-SDI to Component or HDMI inputs, as HD-SDI inputs are not available on some projectors and displays. Also DVI/HDMI extender products using CAT5/6 cabling can be cost effective, provided that cable distance limitations are not exceeded. Different makes and models of modulators are avialable, some take analog HD or SD inputs and other models are available that take HDSDI in for direct digital conversion to a digital channel. Some models can take audio that is embedded in an SDI signal or fed separately as stereo or coax/optical digital audio.
Latency or delay Note that, while HD-SDI and other high definition signals are virtually instant, the encoding process in an January 2012
A control modulator accepts data from software or control system software
HDTV modulator often takes about 1/3 second for 720p, 2/3 second for 1080i. For that reason, you don’t want to use RF as a carrier to areas where that latency will be obvious. For example, if you have an overflow room directly adjacent to the sanctuary or flat panels in the lobby, you might want to use a latency free high definition signal like HD-SDI, component analog or an HDMI/DVI link instead. If the delay won’t be apparent in a room farther away, using HDTV will work fine. There’s also a place for analog channels for live broadcasts as well. For example Willow Creek Community Church broadcasts a live analog channel that feeds seat-back LCD TVs in the handicapped seating areas so when everyone stands up, the participants can still see what’s going on. Or analog channels may be needed to support existing legacy NTSC televisions that you may already have installed.
Adding Off-Air and Cable/Satellite Channels Most churches are uncomfortable including all the channels from cable feeds for good reason. In addition, it’s expensive to rent cable or satellite boxes for every TV location in the site. Also digital cable boxes aren't able to receive your in-house channels, so they are both expensive and inappropriate.
In many cities, off-air channels can feature 10 or more sub-channels of religious programming. For example in Dallas, there are numerous programs available off-air that may not be available from cable or satellite providers. The best solution here is to use off-air converter boxes which can ingest off-air channels then use modulators to provide these ‘selected’ channels into your RF Distribution system. This provides the ministry the ability to have just the channels that they want to provide- not all of them. It’s a great low-cost solution to access free programming. In the case of Cable Television or Satellite channels you want to provide, the solution is to add one or more HDTV modulators fed from a satellite or cable boxes, then combine and modulate these channels to your system. This offers the ability to bring in a variety of programming for news, weather and special events. One site brings men together for football, golf and other sports events. But be careful to make sure you have the appropriate rights to re-distribute the channels to your system; some channels or events require specific licensing fees to provide the content to a distributed system like those in a church or other public venues. u Doug Engstrom is Communications/ Technical Support at Contemporary Reasearch.
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