Got HDTV? Page 3
You can make a TV antenna even more directional by placing additional, smaller versions of the dipole or loop—known as directors—directly in front of the dipole using calculated spacing. The more directors you add, the more directional the antenna becomes. These directors can also be shaped like rods, bow ties, circles, triangles, and squares.
An antenna with an active element, a reflector, and one or more directors is known as a yagi beam antenna. The yagi was developed in the 1920s by two Japanese scientists named Yagi and Uda, and its design is the basis for just about every directional antenna made for TV and FM reception. The majority of TV antennas sold for analog reception are known as log-periodic yagi designs. A log-periodic antenna is a variation of the yagi that can accept TV signals over a wide range of frequencies but doesn't have quite as much gain as a yagi that's designed for a narrow range of frequencies.
Antennas are like photographic lenses. Each type of antenna has a coverage pattern that lets it receive signals over either a wide or a small angle. If most or all of the signals you want to receive come from one location, you'd want an antenna with a narrow angle of reception, such as a multi-element yagi (think zoom or telephoto lens). If you receive signals from more than one direction, you should use an antenna with a wide angle (aperture) of reception (think wide-angle lens). Failing that, you'd need an antenna rotor to aim your antenna for the strongest possible signal.
Practical Antenna Choices
For reception of over-the-air DTV signals, you must first determine if you need lots of gain in a specific direction or coverage over a broad compass range. My experiences have been primarily with TERK, RadioShack, and Channel Master antennas. I haven't had as much experience with Winegard or Blonder Tongue models, but it's safe to say that similar designs from competing manufacturers should provide similar performance—i.e., a suburban UHF yagi antenna from Winegard should work about as well as a comparable Channel Master model.
Local-Reception Outdoor or Attic Antenna
In the Philadelphia market (also in nearby New York, Allentown, and Trenton), the DTV channels are all in the UHF band (for now). The signals from Philadelphia and Allentown are quite strong but originate from points nearly 80 degrees apart on a compass. To receive signals from both cities without a rotor, I selected a Channel Master 4221 four-bay screen antenna, which has a vertically stacked row of bow-tie elements for additional gain. The 4221 is like a wide-angle camera lens: It accepts signals over a range of 75 degrees. I've used it indoors and outdoors with good results. By aiming it between the optimal compass settings for the Philadelphia and Allentown transmission towers (each is about 25 miles from my house), I can pick up all seven DTV stations from both locations and eliminate the need for a rotor. An eight-bay (two stacks of four bow ties) version of this antenna, known as the 4228, is also available. The 4228 provides more gain on lower UHF channels (below channel 50). Above channel 50, it's not quite as good as the 4221, according to Channel Master's own antenna-range tests.
Long-Distance-Reception Outdoor Antenna
While the 4221 does receive DTV signals from New York (65 miles away), the signal levels are very low. To zoom in on these weak signals and provide more gain, I chose a Channel Master 3022/4308 suburban UHF yagi. To improve this antenna's performance, I modified the reflector by trimming its dimensions and changing its position. I also changed the shape of the active bow-tie element that connects to the feedline to improve its resonance at higher UHF frequencies. This modification isn't always necessary, but you can do it with simple tools in about an hour. You can find instructions at www.projectorexpert.com/pages/cm3022.html. Channel Master also makes a longer UHF yagi antenna, known as the 4248 deep-fringe UHF yagi. This design has plenty of additional directors and provides more gain than the 4308. You can use the 4248 to receive DTV stations that are really far away.
RadioShack's 15-2160 and 15-2162 UHF yagis are average performers for DTV reception on channels 14 through 40, but they work better when you connect them to a high-quality UHF preamp. Both antennas use a plain-vanilla half-wave dipole connection instead of a loop. They are moderately directional and feature a multi-element corner reflector. Both antennas have about 1 to 3 dB less gain than their Channel Master counterparts (4308 and 4248).
Indoor-Reception Compact Antenna
For indoor UHF DTV reception, I've used a variety of antennas. The Antiference Silver Sensor antenna (also sold by Zenith) is a compact, 12-inch-long UHF antenna that works well with relatively high signal levels. It connects directly to your set-top box with an attached cable.
I've also had success with RadioShack's 15-1862 indoor VHF/UHF combo antenna. This set-top amplified antenna uses rabbit ears and a figure-8 loop antenna, which you can rotate. The rotatable UHF loop helps compensate for the signal multipath and echoes common to urban environments.
I've even built two small yagis for UHF reception: a 12-inch-long design with three elements and an 18-inch design with five elements. Both use a folded dipole loop as the active element, and both have performed well at indoor test sites in New York and Philadelphia. Keep in mind that indoor reception is very dependent on your DTV set-top receiver's sensitivity. Newer models will quickly lock onto intermittent signals or signals that older DTV set-top boxes can't receive.
VHF and Combo VHF/UHF Outdoor or Attic Antennas
I've tested several combo VHF/UHF antennas with mixed results. Channel Master's 3010 StealthTenna works well with VHF signals, but not so well with UHF. Like many similar models from RadioShack, Winegard, and other manufacturers, Channel Master's 3016 and 3020 antennas performed much better on low and high VHF frequencies than on UHF. That's because the UHF portion of these antennas is very small and doesn't have a lot of gain.
TERK's TV35 VHF/UHF antenna did well with both low-band UHF signals (below channel 40) and VHF signals. If the UHF stations you want to receive are fairly strong, this antenna is worth a look. TERK's PDMA combo VHF/UHF preamp helped boost signals further.
The TERK TV55 (which resembles a long loaf of bread) is a compromise antenna for tight spaces, and you can wall-mount it. It has much more gain in the VHF frequencies than it does in the UHF frequencies, so I can't recommend it for most UHF DTV reception. However, if your DTV signals are really strong on all bands, the TV55 may do the job for you.
Channel Master's SmarTenna is a disc-shaped design with a built-in preamp that's designed for use with motor homes and boats. Like most combo antennas, most of its gain is in the VHF frequencies, but it pulls in strong UHF signals below channel 40 quite well. You can also rotate it to slightly peak the desired signal, but it isn't very good at rejecting interference.
The TERK HDTV60 antenna has been a disappointment. This unique, patented design (helical dipole) works quite well on channels 2 through 6, less so on channels 7 through 13, and not well at all on any UHF channel. The reason? The HDTV60 simply isn't resonant at UHF frequencies, and the built-in preamp doesn't help with UHF reception. The lower-priced TV55 and TV35 (with the PDMA preamp) models easily exceed the HDTV60's performance.