Does it matter if the tv antenna points one way, or 180^ the other?
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From: mm on 1 Dec 2009 00:29 Does it matter if the tv antenna points one way, or 180^ the other? You guys, especially Dave, have convinced me that I need a better (and thus bigger) antenna more than I need an amplified antenna. Does it matter if I point an antenna with several elements of different lengths to the station, or if I point it the exact opposite direction? In my attic, it would be more convenient to do the latter. (I'm too old and at least now, too fat to go on the roof.) Also, I thought 50 miles was the longest range on level ground for a transmitting tower of typical height and an antenna on the roof of a two-story house. So what about a claim that a Wineguard antenna has a range of 75 to 80 miles???? http://estore.websitepros.com/1129733/-strse-159/Winegard-HD-8200U/Detail.bok This antenna is rated for low-band VHF and I don't need that, I've learned, but it's the mileage claim I am asking about. Even this one says: Up to 60 mile VHF range; 45 mile UHF range Don't they get that by mounting it on a 100 foot tower or something? http://www.radioshack.com/product/index.jsp?productId=3739594 And isn't the info obsolete because digital transmitters are working at lower power than analog did? Thanks a lot.
From: Bob AZ on 1 Dec 2009 01:31 > And isn't the info obsolete because digital transmitters are working > at lower power than analog did? > > Thanks a lot. MM Depends on the Front to Back ratio. FWIW the antenna should probably point to the origin of the signal with the shorter elements being the pointing end. And if you are looking at great distances from the source you will probably have to tune the antenna by rotating it while someone observes the picture/TV set. Bob AZ
From: Mark Zacharias on 1 Dec 2009 07:14 "Bob AZ" <rwatson767(a)aol.com> wrote in message news:2c3f4159-201e-4641-af81-b72f5dc91853(a)e4g2000prn.googlegroups.com... >> And isn't the info obsolete because digital transmitters are working >> at lower power than analog did? >> >> Thanks a lot. > > MM > > Depends on the Front to Back ratio. FWIW the antenna should probably > point to the origin of the signal with the shorter elements being the > pointing end. And if you are looking at great distances from the > source you will probably have to tune the antenna by rotating it while > someone observes the picture/TV set. > > Bob AZ Many if not most late model digital format TV receivers have a signal strength indicator available via the menus. This would be very useful, I would think. Mark Z.
From: PlainBill47 on 1 Dec 2009 12:24 On Tue, 01 Dec 2009 00:29:31 -0500, mm <NOPSAMmm2005(a)bigfoot.com> wrote: >Does it matter if the tv antenna points one way, or 180^ the other? > >You guys, especially Dave, have convinced me that I need a better (and >thus bigger) antenna more than I need an amplified antenna. Does it >matter if I point an antenna with several elements of different >lengths to the station, or if I point it the exact opposite direction? >In my attic, it would be more convenient to do the latter. (I'm too >old and at least now, too fat to go on the roof.) > > >Also, I thought 50 miles was the longest range on level ground for a >transmitting tower of typical height and an antenna on the roof of a >two-story house. > >So what about a claim that a Wineguard antenna has a range of 75 to 80 >miles???? >http://estore.websitepros.com/1129733/-strse-159/Winegard-HD-8200U/Detail.bok >This antenna is rated for low-band VHF and I don't need that, I've >learned, but it's the mileage claim I am asking about. > >Even this one says: Up to 60 mile VHF range; 45 mile UHF range Don't >they get that by mounting it on a 100 foot tower or something? >http://www.radioshack.com/product/index.jsp?productId=3739594 >And isn't the info obsolete because digital transmitters are working >at lower power than analog did? > >Thanks a lot. I have to say you are going about this the wrong way. You are choosing to mount the antenna in the attic because it's easier. An indoor mount also has the advantage of reducing exposure to the weather. While this is easier, it has several major disadvantages. You have already mentioned one - difficulty in orienting it properly. There is another - signal attenuation, particularly at higher frequencies. Have you considered the possibility you are focusing on convenience and ignoring performance? As far as antenna range, my parents lived over 60 miles from the transmitter and received good signal levels with an antenna that was mounted less than 15 feet above ground level. PlainBill
From: Dave Platt on 1 Dec 2009 16:48
In article <fd99h51ouj0q2isbuujf2k1qbrkggjip72(a)4ax.com>, mm <NOPSAMmm2005(a)bigfoot.com> wrote: >Does it matter if the tv antenna points one way, or 180^ the other? That depends on the antenna. Typical log-periodic rooftop TV antennas are moderately directional. They have the greatest gain when the small end is pointing towards the transmitter. Directly off of the back, they're usually around 10 dB worse (i.e. one-tenth the power sensitivity). There are some directions around the side which are going to be *extremely* insensitive (very deep nulls). Other sorts of antennas are bidirectional. You'll probably get the best reception from a directional antenna, aimed towards the transmitter (or, sometimes, aimed off at an angle which minimizes the antenna's pickup of reflections from nearby buildings and trees). > You guys, especially Dave, have convinced me that I need a better (and >thus bigger) antenna more than I need an amplified antenna. That's often the case. If your signal level at the TV is low, it's usually better to try to improve it by adding antenna gain, than it is to use an amplifier. An amplifier will boost incoming noise by just as much as it will boost the desired signal. > Does it >matter if I point an antenna with several elements of different >lengths to the station, or if I point it the exact opposite direction? >In my attic, it would be more convenient to do the latter. (I'm too >old and at least now, too fat to go on the roof.) You'll lose a significant amount of sensitivity if you point a traditional log-periodic antenna directly away from the TV station. With a 10 dB front-to-back ratio (typical for a log-periodic) you could cut the antenna range to about a third of what it would be at its best. Let me toss out another idea for you. If you've got attic space which runs long-wise towards, and away from the TV towers, you could install a rhombic antenna. This is simply a diamond-shaped pattern of two wires, with the long axis of the diamond pointing towards / away from the transmitter. The feedline to the TV attaches at one end. At the other end, you can either "terminate" the rhombic with a resistor, or leave the two ends of the wires unconnected. If you terminate the antenna with a resistor, it becomes a unidirectional antenna... the resistor is at the end pointed towards the transmitter, and the feedline attaches at the other end. If you leave the wires at the far end open (unconnected) the rhombic is essentially bidirectional... it can receive signals from stations located off of either end. Rhombics are fairly wide-band antennas. Their impedance is such that yu can probably use a standard 4:1 balun transformer to match them to a 75-ohm coax. They do take up a fair bit of space - each "arm" of the diamond needs to be at least one wavelength long at the lowest frequency you want to receive. The longer, the better (as far as gain goes). A big advantage to them is that they're inexpensive... all you need is wire, a termination resistor (450-to-600-ohm carbon composition will do), and a balun transformer. http://en.wikipedia.org/wiki/Rhombic_antenna has an overview. >Also, I thought 50 miles was the longest range on level ground for a >transmitting tower of typical height and an antenna on the roof of a >two-story house. > >So what about a claim that a Wineguard antenna has a range of 75 to 80 >miles???? >http://estore.websitepros.com/1129733/-strse-159/Winegard-HD-8200U/Detail.bok It depends very much on how high your rooftop is, and how high your mast is, and on the nature of the terrain between you and the transmitter. You can count on some amount of diffraction, which can actually let your antenna "see" a TV transmitter which is below the optical horizon. >This antenna is rated for low-band VHF and I don't need that, I've >learned, but it's the mileage claim I am asking about. > >Even this one says: Up to 60 mile VHF range; 45 mile UHF range Don't >they get that by mounting it on a 100 foot tower or something? >http://www.radioshack.com/product/index.jsp?productId=3739594 "Up to" distance numbers are probably subject to the same sort of marketing inflation, and selective-circumstances picking that affect fuel-economy figures for cars. I'd guess that the upper limits of the "up to" ranges may assume a TV transmitter on top of Mount Wilson (or a similar-sized molehill), an antenna mounted on a tall mast on top of a multi-story apartment building, clear terrain, and perhaps a bit of atmospheric ducting under favorable weather conditions. "We saw a picture once, for 30 seconds, at 80 miles, so the range is up to 80 miles!" >And isn't the info obsolete because digital transmitters are working >at lower power than analog did? "Assumes facts not in evidence." A lot of TV stations had to run their "transition" digital transmitters at lower power than their analog transmitters, for any of a number of technical and legal reasons. Many of them (perhaps most) either boosted their digital transmission power on The Big Day (when the analog transmitters were turned off) or are in the process of doing so as time goes by. TV stations *really* don't like losing area-coverage, since this reduces the number of viewers they can claim, and reduces the value of the commercial-ad time they have available to sell. Stations will tend to want to push up their transmitter power as far as they can afford and/or as far as the FCC will let them. -- Dave Platt <dplatt(a)radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |