Wireless Systems Design

Rabbit Ears And Radios Enter The HD Age

Over 80% of the 110 million homes in the U.S. get their TV via cable, not wireless. Of the remaining 20%, about 12% to 15% get their TV by satellite. The smallest minority still gets local TV over the air. If you have a big-screen high-definition TV set, you probably get your HD channels via cable or satellite service at an extra cost of about $10 per month or more. But did you know that you could get your local HD TV directly off the air for free? Most of you with HDTV probably have two or more HD channels locally, so it is a viable option.

In addition to saving a few bucks, the HD picture will be better. The cable TV company compresses the digital video to get it into those 6-MHz channels. So do the satellite people. And I’m not talking about the original MPEG2 compression that all HDTV goes through to start with. Additional compression/decompression cycles degrade the video to the point where you can really see the difference. Getting the HD signal right out of the air avoids this extra compression and decompression.

But how can you possibly go back to an external TV antenna? It’s easy. Experience has shown that a simple, low-cost external antenna can deliver the best possible HD signal to your TV. If you’re within 10 miles or so of the TV transmitting antenna, indoor rabbit ears may work just fine. Give it a try. If you’re 25 miles or so away, you’ll really need a gain antenna to get the best signal. Gain antennas are very cheap and still available at Radio Shack and online. Models include Yagis, log-periodics, and bow-tie corner reflector types. Just install your antenna as you did back in the dark ages before cable. Put it up as high as you can and point it at the transmitting antenna. If you have several stations, with each in a different direction, you’ll need a rotor.

One good thing about digital HD is that you know when you get the best picture because it’s there in all its glory or not at all. If you don’t have the antenna oriented exactly on target, the signal drops out. You see heavy rectangular pixelation and then nothing.

You can also make your own antenna. At VHF and UHF frequencies, the antenna is pretty short. You can make a half-wave dipole with wire. Cut a piece of 12-gauge copper wire to a length in feet of 468/fMHz. You can find the frequency for each channel at www.arrl.org/tis/info/catv-ch.html. Next, cut the wire in half. Attach an RG-59U or RG-6/U 73-Ω coax to both pieces of wire and the other end of the coax to the ANT input jack of the TV set. Then, orient the dipole broadside to the station antenna.

Don’t forget to review your homeowners association agreement (if you have one). Most associations don’t allow outside antennas. In my neighborhood, outdoor antennas aren’t allowed, except for satellite dishes, which seems selectively hypocritical. If you’re saddled with the same situation, put the antenna in your attic. It will work just as well. You don’t want a nasty note from the neighborhood antenna police.

And one last thing. You’ll also probably need an A-B antenna switch to select between your cable or satellite input and the antenna. You can get one at Radio Shack or online.

HD Radio Progress

You may have heard about high-definition radio, but chances are you still don’t have it. HD Radio is digital radio that is broadcast along with the regular analog radio signal in the same bands and on the same frequencies used for AM and FM radio. The digital signals are compressed and put into an orthogonal frequency-division modulation (OFDM) format. Purely analog radios can’t receive the digital signals.

But HD Radios will decode the digital signals and give you better audio quality than you get now from analog radio. Digital AM radio isn’t quite CD quality, but it’s close, and it’s better than analog. Digital FM radio is definitely CD quality with HD. And in both cases, the digital nature of the signal minimizes fading, noise, and other conditions that affect regular analog AM and FM radio. This will ultimately make HD Radio the wireless of choice in cars.

As of the end of 2006, over 1200 HD Radio stations were on the air. There are probably several HD stations in your area. But you probably haven’t heard them because receivers have been very scarce or very expensive. That’s changing rapidly, though. Most car manufacturers now offer HD as an option. You also can buy a tabletop HD Radio at one of the major consumer electronics stores. Best Buy recently added HD to its lineup, joining Radio Shack, Tweeter, Circuit City, the Sharper Image, Costo, Wal-mart, and dozens of local electronic dealers. You can get them online at Amazon and Crutchfield too. I have a cool-looking Boston Acoustic HD and a Radiosophy unit on order.

With its compression technology, HD Radio can offer several channels of voice in the same bandwidth as a normal analog signal. Called HD2, stations can become two, three, or more separate stations broadcasting different content at the same time. This gives you more programming choices than ever before—and multiplies the advertising potential. Be sure to get a radio with HD2 capabilities, which earlier HD Radio models didn’t have.

HD Radio can also transmit the name of the song title and artist in addition to other info. News and traffic transmissions are possible too. Microsoft has signed up with Clear Channel (CC) Radio, the largest radio broadcasting company in the U.S., to build a nationwide data delivery service using HD Radio technology. Besides news and traffic info, it may include weather, movie schedules, sports results, stock data, and whatever.

HD Radio has taken years to be developed and then brought to the consumer. While it’s finally here, it’s still emerging. For more information, go to www.hdradio.com and www.ibiquity.com. Give HD a try if you haven’t already. And remember, unlike the satellite digital radio from Sirius and XM, HD Radio is free!

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