HOW DO I SELECT THE RIGHT ANTENNA? ASK A FOOL
One day while reading the site of home theater consultant Peter Putnam at http://www.hdtvexpert.com/ I came across a link to a Web site that I feel may be very useful in determining if a household has enough antenna to ensure their new DTV tuners, be it a new set, a converter box, or a DTV tuner in an HD satellite TV receiver, will get their local channels after the DTV conversion completes. One word of caution - comparing this site to http://www.antennaweb.org/ is like comparing Linux to Windows; it takes a bit of work and practice, but in the end, the system runs a lot better for what you need.
The site is http://www.tvfool.com/, and it has a signal predictor tool for any address in the United States, and it uses the latest FCC data of the stations' broadcast facilities, including those that will be the final DTV post-transition broadcasts. This will allow an antenna user to do a "before" and "after" comparsion to see which stations will change their final DTV broadcast frequency, and if they would expect a stronger DTV post-transition signal, or not.
Like antennaweb.org, which has been promoted more and more by the NAB in their TV PSAs, the TV Fool signal predictor asks for your address for best results, although a zip code is all that is needed. You can also enter GPS coordinates and antenna height for your location for the best results, and if your area is in hilly terrain, then you will have to make sure the results are right at your location.
The results allow the user to not only view the results on the Web browser, but also save a graphic image of the results that can be saved and printed offline. The image file resolution is good enough to zoom in on the image to read the information closely, if needed.
One thing I really enjoy about the TV Fool predictor is on their FAQ page, they provide a detailed explanation on how to interpret the results, something I feel the antennaweb.org site lacks. The trick is to ensure the antenna signals maintain the best signal to noise ratio (SNR) from the antenna to the DTV tuner. The site stresses to notice their Noise Factor number. In the end, if the number is above zero, then the DTV tuner should provide a good picture, although because actual signal varies with the weather, I would set a goal to make that number 5 to 10 to allow for "rain fade" or unstable air effects that reduce signal at the antenna from time to time.
Here is how it works - the results are listed from the strongest signal to the weakest. It is important to note that successful reception always starts at the antenna, and that amplifiers cannot pull in more signal; they only overcome signal losses in splitters and cables. If you have an antenna with a spec sheet showing antenna dB gain, then you can start by adding the gain to the station Noise Factor result. The channel to use must be the Real channel listed; the "virtual channel" is the station you tune your DTV tuner to watch that primary channel. If the antenna specs are listed as dBi, then you must reduce the result by 2.1 to convert to dBd gain. If the station post-DTV transition Noise Factor is at or below zero after adding antenna gain, then if you want to watch that channel, then you will have to consider buying a larger antenna because an amplifier will not do much good.
On the other hand, if the results are above zero, then so far, so good. Now comes the issue of cable and splitter loss. If you are using a two way splitter, subtract 4 from each result, and subtract 7 for a four way splitter. For every 100' length of RG-6 type cable, subtract 1 dB for real channels 2-6, 2 dB for real channels 7-13, and 4 dB for real channels 14-69 (14-51 post DTV transition). If at any point the noise factor results fall below zero, then an amplifier is needed to offset this loss. You will need to start again, however. After adjusting for antenna gain, subtract the number 4 from each result. This accounts for the noise figure of the amplifier you are going to use, which should be a low noise amplifier. Then, add the results to the amplifier gain, and subtract the cable/splitter losses as noted above. If the results come in above zero, then your system is set.
A couple other notes - the results, like antennaweb.org, use a color coded system, but this one is more practical. If the stations are listed as green, then chances are good that an indoor antenna should suffice for your location, because the predicted noise factor numbers are very high that the signals should still be fairly strong indoors after being lost through the building. Results listed in yellow may be receivable by an attic-mounted antenna, since the predicted noise factors are around 15, accounting for likely signal losses through roof shingles on plywood among other typical attic structures, plus the fact that the antenna is mounted higher than an indoor antenna.
The site also determines if the predicted signals will be line of sight (LOS), diffracted, or tropospheric. Line of sight signals will be easy to receive as long as the antenna is properly aimed. Diffracted signals may require the antenna to be raised or lowered slightly to receive the signal adequately. The tropospheric signals are the weakest and come from out of market, and are receivable only on very rare occasions when the atmosphere allows it.
Comparing the results for my area, they work out very well; it is in agreement with some Chicago stations I can receive indoors as opposed to the strong large directional rooftop antenna I normally use for DTV reception. This also gives me confidence that my existing antenna system will continue to receive all the local DTV channels post-transition. So if you find that antennaweb.org color guide a bit confusing and reminiscent of Trivial Pursuit, give http://www.tvfool.com/ a try - you just might find the antenna answers you have been desperately seeking.
One day while reading the site of home theater consultant Peter Putnam at http://www.hdtvexpert.com/ I came across a link to a Web site that I feel may be very useful in determining if a household has enough antenna to ensure their new DTV tuners, be it a new set, a converter box, or a DTV tuner in an HD satellite TV receiver, will get their local channels after the DTV conversion completes. One word of caution - comparing this site to http://www.antennaweb.org/ is like comparing Linux to Windows; it takes a bit of work and practice, but in the end, the system runs a lot better for what you need.
The site is http://www.tvfool.com/, and it has a signal predictor tool for any address in the United States, and it uses the latest FCC data of the stations' broadcast facilities, including those that will be the final DTV post-transition broadcasts. This will allow an antenna user to do a "before" and "after" comparsion to see which stations will change their final DTV broadcast frequency, and if they would expect a stronger DTV post-transition signal, or not.
Like antennaweb.org, which has been promoted more and more by the NAB in their TV PSAs, the TV Fool signal predictor asks for your address for best results, although a zip code is all that is needed. You can also enter GPS coordinates and antenna height for your location for the best results, and if your area is in hilly terrain, then you will have to make sure the results are right at your location.
The results allow the user to not only view the results on the Web browser, but also save a graphic image of the results that can be saved and printed offline. The image file resolution is good enough to zoom in on the image to read the information closely, if needed.
One thing I really enjoy about the TV Fool predictor is on their FAQ page, they provide a detailed explanation on how to interpret the results, something I feel the antennaweb.org site lacks. The trick is to ensure the antenna signals maintain the best signal to noise ratio (SNR) from the antenna to the DTV tuner. The site stresses to notice their Noise Factor number. In the end, if the number is above zero, then the DTV tuner should provide a good picture, although because actual signal varies with the weather, I would set a goal to make that number 5 to 10 to allow for "rain fade" or unstable air effects that reduce signal at the antenna from time to time.
Here is how it works - the results are listed from the strongest signal to the weakest. It is important to note that successful reception always starts at the antenna, and that amplifiers cannot pull in more signal; they only overcome signal losses in splitters and cables. If you have an antenna with a spec sheet showing antenna dB gain, then you can start by adding the gain to the station Noise Factor result. The channel to use must be the Real channel listed; the "virtual channel" is the station you tune your DTV tuner to watch that primary channel. If the antenna specs are listed as dBi, then you must reduce the result by 2.1 to convert to dBd gain. If the station post-DTV transition Noise Factor is at or below zero after adding antenna gain, then if you want to watch that channel, then you will have to consider buying a larger antenna because an amplifier will not do much good.
On the other hand, if the results are above zero, then so far, so good. Now comes the issue of cable and splitter loss. If you are using a two way splitter, subtract 4 from each result, and subtract 7 for a four way splitter. For every 100' length of RG-6 type cable, subtract 1 dB for real channels 2-6, 2 dB for real channels 7-13, and 4 dB for real channels 14-69 (14-51 post DTV transition). If at any point the noise factor results fall below zero, then an amplifier is needed to offset this loss. You will need to start again, however. After adjusting for antenna gain, subtract the number 4 from each result. This accounts for the noise figure of the amplifier you are going to use, which should be a low noise amplifier. Then, add the results to the amplifier gain, and subtract the cable/splitter losses as noted above. If the results come in above zero, then your system is set.
A couple other notes - the results, like antennaweb.org, use a color coded system, but this one is more practical. If the stations are listed as green, then chances are good that an indoor antenna should suffice for your location, because the predicted noise factor numbers are very high that the signals should still be fairly strong indoors after being lost through the building. Results listed in yellow may be receivable by an attic-mounted antenna, since the predicted noise factors are around 15, accounting for likely signal losses through roof shingles on plywood among other typical attic structures, plus the fact that the antenna is mounted higher than an indoor antenna.
The site also determines if the predicted signals will be line of sight (LOS), diffracted, or tropospheric. Line of sight signals will be easy to receive as long as the antenna is properly aimed. Diffracted signals may require the antenna to be raised or lowered slightly to receive the signal adequately. The tropospheric signals are the weakest and come from out of market, and are receivable only on very rare occasions when the atmosphere allows it.
Comparing the results for my area, they work out very well; it is in agreement with some Chicago stations I can receive indoors as opposed to the strong large directional rooftop antenna I normally use for DTV reception. This also gives me confidence that my existing antenna system will continue to receive all the local DTV channels post-transition. So if you find that antennaweb.org color guide a bit confusing and reminiscent of Trivial Pursuit, give http://www.tvfool.com/ a try - you just might find the antenna answers you have been desperately seeking.
posted by Derek (IA) | 5:18 PM
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2 comments
