CAN I IMPROVE THE PERFORMANCE OF AN HDTV ANTENNA?



This time I would like to present a suggestion that might improve the performance of a few antennas in the the market for certain locations. Specifically, they are available antennas that are directional on UHF (frequency assignments 14-69) and bi-directional on VHF high band (frequency assignments 7-13). There are antennas out there that are branded as HDTV antennas, but if you see such an antenna to get off-air HDTV broadcasts, this branding is a serious case of "let the buyer beware". Several of these branded HDTV antennas that are small and attractive may really be nothing more than directional UHF antennas. While they may be great for getting off-air HDTV broadcasts on frequency assignments 14-69 that are coming in from about the same compass direction (this information for your specific location may be found by using http://www.antennaweb.org/), if you have available off-air DTV broadcasts on VHF frequency assignments 2-13, that so-called HDTV antenna may not get all your channels. Those small nice looking antennas are not tuned for 2-13, so their reception of such channels is very limited in terms of distance; they may get UHF channels from 50 miles out, but the best some can do for 7-13 is 30 miles, and even less for 2-6.

There is another issue -- suppose you do have one of these small HDTV branded antennas, and they are getting all your local HD broadcasts. Well when your analog off-air TV tuners stop working after February 17, 2009, those effective antennas may suddenly not get all your local off-air channels that are exclusively digital. Right now the FCC is allowing analog and digital over-the-air broadcasts from channels 2-69, and in some markets all the digital broadcasts are on UHF, but not all. The FCC has ordered broadcasters to select a final DTV frequency assignment from 2-51 that will be effective following the analog shutoff, so frequencies allocated for TV broadcasting on channels 52-69 (702-806 MHz, or the "700 MHz band"), will be freed up for new wireless applications, including for homeland security. So, some stations now using channels 52-69 for digital off-air broadcasting will HAVE to relocate their DTV channel. In addition, station broadcast engineers are willing to select a final DTV of-air assignment on VHF high band, channels 7-13, as those channels can cover a viewing area with less power than UHF stations. So, if you are using a UHF antenna only for off-air DTV broadcasts, you may want to check to see if 14-69 will be the final assignments, because if they are not, there is a chance you may need to replace that once functional antenna.

You can get a heads up on which channels will be the final digital TV assignments by going to http://www.fcc.gov/dtv which is a DTV page that has notices on the broadcast TV transition to digital available for public viewing and use at no charge. You can download the MS Office or Acrobat notices on the page, whichever format you prefer. There are three rounds of final channel elections that took place over the past year and a half. The tentative final assignments for the first and second rounds are listed on the documents dated 5/23/06, while tentative assignments for round 3 are listed on the documents dated 8/29/06. You will need to use http://www.antennaweb.org/ and pay attention to the city the station is located -- there is a chance that a few local stations are based out of your state of residence. For instance, WPWR, the My Network TV affiliate out of Chicago, is actually based in Gary, Indiana. Another example is WWOR out of New York, which is actually based out of Secaucus, New Jersey. As I said, these post-analog shutdown channel assignments are TENTATIVE, and a few stations, including WABC, the ABC affiliate from New York, are still disputing their final elected channel with the FCC. Once al these issues are resolved, which hopefully will be by year's end, the FCC will release a "final table of DTV allotments" which should have the official secured list of the station assignments for exclusive digital broadcasting, and once I see that table posted, I will let you know in a future blog post.

So, suppose you realize that you need an antenna for channels 7-69 as a long term solution, so that after February 17, 2009, you can simply rescan your DTV tuner to get all your broadcasts instead of readjusting your antenna. Here now I offer a few truths and a couple tricks. First, it is possible that some UHF antennas can get that one or two VHF high band (7-13) frequency assignment DTV channels. I have found that the popular bowtie UHF antennas, like Channel Master's 4228 and Winegard's PR-4400 and PR-8800, do have bi-directional VHF reception on 7-13, although with less mileage range than UHF. By "bi-directional" I mean the antenna can receive signals from both the front of the antenna, and the backside of the antenna, but not off the sides. Bi-directional antennas may be good in open areas with little obstructions, but in areas where ghost-causing signals may come in off the back, that may be a problem, as these signals will break up DTV pictures.

Meanwhile, the highly lauded Silver Sensor is a good UHF directional antenna which great rejection of unwanted signals from behind. However for VHF high band, this antenna has an issue. The antenna has a phase line inside the antenna that pretty much cancels any chance of receiving unwanted UHF signals from behind that could cause picture breakup. However, I have found that the same line can receive VHF high band, but unlike some UHF antennas, the Silver Sensor can only receive frequency assignments 7-13 OFF THE SIDE, which means in areas where DTV signals are on 7-13, a user may need to turn the antenna just to get those channels, and that could become a tiresome inconvenience.

As a result, TERK, a division of Audiovox, took the Silver Sensor design concept and added a fixed dipole for channels 7-13 for their HDTVo model for outdoor and attic installs, and a telescoping "rabbit-ear" like adjustable dipole for their HDTVi indoor antenna, as well as good VHF/UHF isolation between the elements. By the way, there is also an amplified version of the HDTVi available, the HDTVa. Philips appears to be selling a similar concept to the TERK HDTVa, the model PHDTV3, with a more attractive and low-profile design and a 10 dB amplifier. I would personally recommend indoor antennas with a gain no more than 15 dB, as higher gain versions may deliver saturated or overpowered signals into your DTV tuner. Radio Shack also has an attractive amplified model for outdoor and attic installs, model 15-2187, that is directional for UHF and bi-directional and tuned for frequency assignments 7-13. Finally, there is the simple yet tried and true Winegard Sensar III "batwing" antenna (GS-1000 nonamplified, GS-2200 amplified) that is bi-directional on 7-13 and directional on UHF 14-69 with a wide look angle for outdoor and attic installs.

However all the models I listed in the paragraph above are bi-directional on 7-13, and that may be a problem in areas of high ghosting for those particular channels. As of now, the one antenna I know of that is directional on channels 7-69 is the Winegard SharpShooter SS-3000, and Winegard is now about to come out with a kit for outdoor installation of this antenna, which has a 10-12 dB amplifier, just the right amount of amplifier gain when needed. But what about the other antennas I mentioned? Well, here is a trick you can try to make bi-directional antennas on 7-13 directional, which would reject ghosting from behind, and possibly pull in stronger 7-13 signals. For the models used for outdoor or attic installation, if your home has aluminum sided walls or the walls have foil-backed insulation, you could mount the antenna with its backside 7 to 8 inches from the wall, or, for an attic install, place some aluminum material, even aluminum foil, or metal meshing, behind the antenna. The material would have to have a rectangular geometry width a length at least 10% longer than the width of the antenna, and at least 10% higher than the height of the antenna. Again, the material would be placed 7 to 8 inches from the back of the antenna. The metal material would then become a reflector of energy on channels 7-13, and it would block unwanted signal from behind while increasing reception from the front. It is just like a lens on a flashlight focusing light in a single direction. For the antennas I listed, there should be little effect on the UHF performance since the antenna design is already focusing its energy on UHF 14-69 reception regardless of what is behind the antenna.

For the indoor antennas, if there is a metallic backed cabinet or wall that the antenna can fit in, but NOT on a metallic shelf, then you could try the antenna in that space, and if there are telescoping elements, try the elements fully retracted and parallel to the floor first. Again, make sure there is a 7 to 8 inch space between the metal backing and the telescoping elements, which are for VHF reception, for best results. Finally, it would not hurt to use the existing analog antenna tuner to check for picture quality from channels 7 through 13, because if they look good with little ghosting, your current antenna should be all set to get the exclusively digital broadcasts after February 17, 2009.

Now I need to finish with a disclaimer -- what I recommended is for areas with TV signals generally available from a single direction for receiving frequency assignments 7-69. At last check there are about 50-60 stations in the United States looking to use channels 2-6 as their final DTV assignments. In addition, there are markets with DTV broadcasts currently available from 2-6, so I do recommend using http://www.antennaweb.org/ and paying attention to the "frequency assignment" column in the results, as well as looking at the FCC reports for your area. If you need 2-6 reception, there will be other issues to consider that will be addressed on a future blog entry -- until then, you may need to do some more research -- and be willing to use a large antenna.