WHY IS ONE ANTENNA BETTER THAN ANOTHER?
There will never be one single antenna that will work everywhere in the US due to the fact that not all households have all the local HD transmissions from a single location. Oh there are some, most notably Los Angeles where just about every LA and Orange County based TV station has their digital transmission from one area on Mount Wilson just north of Pasadena. In this case a directional antenna is great. However, in other areas, like San Francisco, a household may have their local TV transmissions in a couple locations; most of the DTV transmissions are from the Sutro Tower along the bay, but NBC HD is available from San Jose, requiring a multi-directional antenna in some areas, or a directional antenna on a rotor.
In those areas, if a household has all their local HD within 30 miles in multiple directions, an omnidirectional antenna may suffice – if the neighborhood is RF friendly enough. I would consider an RF friendly neighborhood to be either a run-of-the mill suburban type that was the setting of family-friendly 1960’s sitcoms, or a rural area over flat terrain. If the neighborhood is surrounded by tall buildings or trees, or deep in a valley where TV transmissions could pass over, the household will deal with either no signal or multiple reflective signals (multipath) that cause ghosting on analog TV pictures, and loss of DTV picture. If you are just seeing this entry, to get the details on how multipath can kill a DTV signal, click on the 08-21-05 “Archives” link. The archive will provide a background for what follows.
In areas of heavy multipath, or signal blockage, an antenna user would definitely require a directional antenna. If a user of CheckHD.com notes on the antenna selector that there are obstructions, the selector will automatically recommend a minimum medium directional (red map) antenna, not so much because of the gain of the antenna, but the ability to reject multipath signals. The CEA qualifies a medium directional antenna as one with a front-to-back ratio of 12 dB or more, which means the antenna will deliver 75% or more LESS signal picked up by the antenna than the front, and if the front of the antenna is pulling in the most desirable signal, the picture quality should be pretty good.
In areas of high multipath or obstructed areas, that most desirable signal likely will NOT come from the expected direction of the TV signal. That signal may be blocked or interfered, and a reflected multipath signal may be good enough for a DTV tuner to decode, as long as undesired signals are rejected by the antenna to the point where the DTV signal is flat enough. DTV tuners have become more able to deal with received signals that are not very flat thanks to bit-error correction algorithms in the tuner chipset, most notably the 4th and 5th generation chipsets designed by LG/Zenith, which when used in the right areas MAY allow a less expensive multidirectional antenna to do the job.
However, even with advanced DTV chipsets it would not hurt to use a good antenna to keep the received DTV signals as flat as possible, thus keeping the channel signal strength up. In addition, I myself haven’t had a chance to see these advanced tuners receive DTV signals with old-fashioned bi-directional rabbit ears in a high ghosting area, like a downtown urban area surrounded by tall buildings, so as an antenna guy I remain a bit skeptical. So let me give my analysis on some popular antennas used and praised on other HDTV blogs and boards on why they may be doing the job and are highly recommended, most of them are UHF, and a few are made by Winegard.
Before that I will start with a regular Yagi style antenna that is large and still may be sticking out on a rooftop. Directional ones have the front-to-back ratio, but there does exist the possibility that such antennas may pick up a reflected signal from the ground, or even the sky due to scattering from the atmosphere during daylight hours or high humidity, or even trees in a certain spot. A height adjustment of a Yagi may suffice in some cases, but some have seen improvement by stacking a pair of identical Yagis in an array. A vertical stack is like closing Venetian blinds on light; the energy becomes more focused on getting signal power from a straight direction while rejecting reflected signal from the sky and ground. Another idea is a horizontal stack which is like putting blinders on a horse; the energy is again more focused straight ahead by narrowing the side-to-side antenna beamwidth, reducing potential multipath from the SIDES of the antenna.
This array stacking is the reason why a bowtie antenna, most notably the ChannelMaster 8-bay 4228, has been a noted UHF directional antenna faring well for DTV reception (Winegard has a similar model, the PR-8800). There are 8 UHF drive elements, 4 vertically stacked in 2 horizontal arrays. The result has a forward pencil-beam gain focusing on just the DTV line-of-sight signals and not so much the reflected signals from the sides, ground, and sky, unlike a traditional Yagi antenna of similar gain. In addition, the reflector grid behind the drive elements provide the desired front-to-back ratio, and the size of the reflector becomes a larger brick wall that becomes more impassable by undesired signals from behind. The downside of such an antenna is that if desired DTV signals are spaced at least 30 compass degrees apart, the 8-bay’s on-a-dime focus may MISS one set of signals. As a result, an antenna with a wider beam width may fare better in a fixed position, like the ChannelMaster 4224 (or Winegard PR-4400).
Another popular DTV antenna is the Zenith Silver Sensor, sort of a Yagi UHF, more log periodic throughout the UHF band, which was designed with a very high front-to-back ratio (I’ve measured it at 20 dB on some UHF channels). This has about the same beam width as a 4-bay bowtie, so this has proven to be a good directional UHF DTV antenna. The SquareShooter (Winegard SS-1000 or TERK HDTVs) and SharpShooter (Winegard SS-3000 or TERK HDTVlp) antennas I have helped develop at Winegard use a different type of means to get medium directional front-to-back, a GRID printed with a conductive ink on plastic. The grids are arranged to essentially load and scatter undesired signals from behind the assembly, preventing them from being transferred on the drive elements. The SharpShooter drive element is a simple pair for high band VHF and UHF reception with the scatter plane on the grid doing its part to ensure the DTV signals stay flat en route to the tuner; same case with the SquareShooter, which is larger, and more capable in outdoor high ghosting areas. The SquareShooter drive element is a sinous pair that is more broadbanded in UHF, to keep it matched to the cable and tuner, this also helps maintain the flatness of the received DTV signals, and the reason we have been able to claim the antenna’s ability to perform well in high ghosting antennas, or as our marketing peeps say, “solves problems other antennas cannot solve”. The patent for the SquareShooter antenna was officially granted in July 2005, and can be viewed at http://www.uspto.gov/, just search #6,922,179 (gee, who will nab the lucky 7 millionth?) for more information (I didn’t get the design credit, nor do I deserve, the gentleman who did get the idea and did most of the development, but I did write most of the “BACKGROUND” section!).
So there is a summary of the different antennas out there and why they can do what they can for DTV reception. Despite all advances for corrective DTV tuners, the antenna still remains the key in getting the over-the-air signal in the first place, and as long as its properties and features can dress up the signal so it looks presentable upon entry into a DTV tuner, the viewer will enjoy a colorful and spectacular feast for the eyes. Thanks for viewing, and again, feel free to leave comments or find my contact link on my profile!
There will never be one single antenna that will work everywhere in the US due to the fact that not all households have all the local HD transmissions from a single location. Oh there are some, most notably Los Angeles where just about every LA and Orange County based TV station has their digital transmission from one area on Mount Wilson just north of Pasadena. In this case a directional antenna is great. However, in other areas, like San Francisco, a household may have their local TV transmissions in a couple locations; most of the DTV transmissions are from the Sutro Tower along the bay, but NBC HD is available from San Jose, requiring a multi-directional antenna in some areas, or a directional antenna on a rotor.
In those areas, if a household has all their local HD within 30 miles in multiple directions, an omnidirectional antenna may suffice – if the neighborhood is RF friendly enough. I would consider an RF friendly neighborhood to be either a run-of-the mill suburban type that was the setting of family-friendly 1960’s sitcoms, or a rural area over flat terrain. If the neighborhood is surrounded by tall buildings or trees, or deep in a valley where TV transmissions could pass over, the household will deal with either no signal or multiple reflective signals (multipath) that cause ghosting on analog TV pictures, and loss of DTV picture. If you are just seeing this entry, to get the details on how multipath can kill a DTV signal, click on the 08-21-05 “Archives” link. The archive will provide a background for what follows.
In areas of heavy multipath, or signal blockage, an antenna user would definitely require a directional antenna. If a user of CheckHD.com notes on the antenna selector that there are obstructions, the selector will automatically recommend a minimum medium directional (red map) antenna, not so much because of the gain of the antenna, but the ability to reject multipath signals. The CEA qualifies a medium directional antenna as one with a front-to-back ratio of 12 dB or more, which means the antenna will deliver 75% or more LESS signal picked up by the antenna than the front, and if the front of the antenna is pulling in the most desirable signal, the picture quality should be pretty good.
In areas of high multipath or obstructed areas, that most desirable signal likely will NOT come from the expected direction of the TV signal. That signal may be blocked or interfered, and a reflected multipath signal may be good enough for a DTV tuner to decode, as long as undesired signals are rejected by the antenna to the point where the DTV signal is flat enough. DTV tuners have become more able to deal with received signals that are not very flat thanks to bit-error correction algorithms in the tuner chipset, most notably the 4th and 5th generation chipsets designed by LG/Zenith, which when used in the right areas MAY allow a less expensive multidirectional antenna to do the job.
However, even with advanced DTV chipsets it would not hurt to use a good antenna to keep the received DTV signals as flat as possible, thus keeping the channel signal strength up. In addition, I myself haven’t had a chance to see these advanced tuners receive DTV signals with old-fashioned bi-directional rabbit ears in a high ghosting area, like a downtown urban area surrounded by tall buildings, so as an antenna guy I remain a bit skeptical. So let me give my analysis on some popular antennas used and praised on other HDTV blogs and boards on why they may be doing the job and are highly recommended, most of them are UHF, and a few are made by Winegard.
Before that I will start with a regular Yagi style antenna that is large and still may be sticking out on a rooftop. Directional ones have the front-to-back ratio, but there does exist the possibility that such antennas may pick up a reflected signal from the ground, or even the sky due to scattering from the atmosphere during daylight hours or high humidity, or even trees in a certain spot. A height adjustment of a Yagi may suffice in some cases, but some have seen improvement by stacking a pair of identical Yagis in an array. A vertical stack is like closing Venetian blinds on light; the energy becomes more focused on getting signal power from a straight direction while rejecting reflected signal from the sky and ground. Another idea is a horizontal stack which is like putting blinders on a horse; the energy is again more focused straight ahead by narrowing the side-to-side antenna beamwidth, reducing potential multipath from the SIDES of the antenna.
This array stacking is the reason why a bowtie antenna, most notably the ChannelMaster 8-bay 4228, has been a noted UHF directional antenna faring well for DTV reception (Winegard has a similar model, the PR-8800). There are 8 UHF drive elements, 4 vertically stacked in 2 horizontal arrays. The result has a forward pencil-beam gain focusing on just the DTV line-of-sight signals and not so much the reflected signals from the sides, ground, and sky, unlike a traditional Yagi antenna of similar gain. In addition, the reflector grid behind the drive elements provide the desired front-to-back ratio, and the size of the reflector becomes a larger brick wall that becomes more impassable by undesired signals from behind. The downside of such an antenna is that if desired DTV signals are spaced at least 30 compass degrees apart, the 8-bay’s on-a-dime focus may MISS one set of signals. As a result, an antenna with a wider beam width may fare better in a fixed position, like the ChannelMaster 4224 (or Winegard PR-4400).
Another popular DTV antenna is the Zenith Silver Sensor, sort of a Yagi UHF, more log periodic throughout the UHF band, which was designed with a very high front-to-back ratio (I’ve measured it at 20 dB on some UHF channels). This has about the same beam width as a 4-bay bowtie, so this has proven to be a good directional UHF DTV antenna. The SquareShooter (Winegard SS-1000 or TERK HDTVs) and SharpShooter (Winegard SS-3000 or TERK HDTVlp) antennas I have helped develop at Winegard use a different type of means to get medium directional front-to-back, a GRID printed with a conductive ink on plastic. The grids are arranged to essentially load and scatter undesired signals from behind the assembly, preventing them from being transferred on the drive elements. The SharpShooter drive element is a simple pair for high band VHF and UHF reception with the scatter plane on the grid doing its part to ensure the DTV signals stay flat en route to the tuner; same case with the SquareShooter, which is larger, and more capable in outdoor high ghosting areas. The SquareShooter drive element is a sinous pair that is more broadbanded in UHF, to keep it matched to the cable and tuner, this also helps maintain the flatness of the received DTV signals, and the reason we have been able to claim the antenna’s ability to perform well in high ghosting antennas, or as our marketing peeps say, “solves problems other antennas cannot solve”. The patent for the SquareShooter antenna was officially granted in July 2005, and can be viewed at http://www.uspto.gov/, just search #6,922,179 (gee, who will nab the lucky 7 millionth?) for more information (I didn’t get the design credit, nor do I deserve, the gentleman who did get the idea and did most of the development, but I did write most of the “BACKGROUND” section!).
So there is a summary of the different antennas out there and why they can do what they can for DTV reception. Despite all advances for corrective DTV tuners, the antenna still remains the key in getting the over-the-air signal in the first place, and as long as its properties and features can dress up the signal so it looks presentable upon entry into a DTV tuner, the viewer will enjoy a colorful and spectacular feast for the eyes. Thanks for viewing, and again, feel free to leave comments or find my contact link on my profile!
posted by Derek (IA) | 7:45 PM
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2 comments
