An Antenna is an Antenna, Right? Page 2
The Magnadyne yagi takes us back to the classic rooftop antenna from the dawn of TV. Because it's designed for UHF only, it's quite a bit smaller than the multiband rooftop antenna that used to be so popular. It's 20 inches wide and 43 inches long, and it weighs only 3 pounds.
The Big City
Chicago currently has two digital stations claiming to be on the air, WFLD-DT (channel 31, a Fox O&O) and WBBM-DT (channel 3, a CBS O&O). However, the day of our test, WBBM-DT wasn't on the air, possibly because of reports that broadcasts were interfering with local cable boxes. WFLD-DT was being sent from the Sears Tower on one of the temporary antenna towers built to accommodate DTV. In most instances, digital television's broadcast tower location isn't optimal. The prime broadcast tower locations are still reserved for the analog signal. The reason for this is simple: Most people are still watching analog channels. When the tide turns and the primary revenue stream becomes the digital channel, the broadcasters will switch the prime locations.
I loaded up my DTV field-test vehicle, used exclusively for Home Theater (actually, my Ford Explorer with the baby seat taken out and the rear seats folded down) with the antennas, a Wavetek spectrum analyzer, a Sencore field-strength meter, an AC generator, a global-positioning system, an analog TV, an HD monitor, and a Unity Motion DTV tuner (Unity Motion? Hey, the price was right. What can I say?). Good thing I was in Chicago and not L.A., or else I might have been arrested for being an overt geek in public.
I tested all three antennas at six sites. Moving northwest in a straight line away from the city, I stopped at 1, 2, 4.5, 10, 20, and 30 miles away from the broadcast tower, as measured by my GPS.
The antennas were tested primarily on three criteria. The first is signal strength (the amount of signal that was received), measured in decibels and microvolts. Tilt, the second criteria, is the difference between the level of the front end of the signal compared with the back. The DTV signal is basically a square wave, and the signal should be flat across its 6-megahertz channel spectrum so that the TV tuner can do its job easily. This is also measured in dB, and there should be no more than 4 dB of tilt. In audio terms, tilt would be a flat frequency response. The final criteria is picture performance, which is based on observation of the picture produced by the DTV signal for a period of one minute. I noted any artifacts, such as the picture freezing or tiling, and whether or not the picture came in at all.
I also used an analog TV for comparing digital versus analog reception and to check for ghosting (multipath).