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fractals and HDTV antennas
Hi:
A month or so ago I say a PBS piece on fractals. The piece claimed that the "technology" is used to make the antennas for cell phones. Have any amateurs used "fractal technology" to form their antennas? Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? Yours, JLG |
fractals and HDTV antennas
On Wed, 30 Sep 2009 00:46:28 -0400, "John Gilmer"
wrote: Hi: A month or so ago I say a PBS piece on fractals. The piece claimed that the "technology" is used to make the antennas for cell phones. Have any amateurs used "fractal technology" to form their antennas? -sigh- Any? Yes. Many? No. Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? They work about as hard as Bernie Madoff worked. The most enthusiastic fractal supporters here are those who never built any, couldn't show you a design if they were forced to google for one, and pound their breast about how modern inventors are reviled in their own neighborhood. The most successful merchant who has dared post here would sue you if you tried to make your own. What's inside them? Wire (metal). Same as any antenna. What makes you ask? 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
"John Gilmer" wrote in message net... Hi: A month or so ago I say a PBS piece on fractals. The piece claimed that the "technology" is used to make the antennas for cell phones. That might be true. There's certainly material on the www about research into fractal antennas that can be Googled, such as http://ceta.mit.edu/pierb/pierb14/07.09030802.pdf Have any amateurs used "fractal technology" to form their antennas? Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? As you may realise, terrestrial broadcasting provides a large margin for a lot of households which makes it possible to receive good signals in some areas using a dead sheep. Consequently indoor television antennas are sold in a variety of styles and, at some locations, some of them work - even if they have meagre electrical characteristics. Unfortunately, there is a tendency for unqualified folklore to arise about antennas that appear to work (in particular circumstances). The DVB-T system used in Europe is particularly resistant to multipath distortion, which helps. Some book-sized efforts contain a PCB bow tie in front of a plane reflector. In others, the shapes of the elements are fiddled around with like http://www.instructables.com/id/How_...DTV_DTV_plus_/ Chris |
fractals and HDTV antennas
Wow. Been a while. Last time I saw or wrote anything here about fractals was
over ten years ago, and someone in the group threatened to sue me/everyone who was not a supporter of the technology. I do know that I have seen mention of this technology relative to hand held ATSC receivers for mobile video (cel phones, etc) GeorgeC "John Gilmer" wrote in message net... Hi: A month or so ago I say a PBS piece on fractals. The piece claimed that the "technology" is used to make the antennas for cell phones. Have any amateurs used "fractal technology" to form their antennas? Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? Yours, JLG |
fractals and HDTV antennas
"John Gilmer" wrote in message net... Hi: A month or so ago I say a PBS piece on fractals. The piece claimed that the "technology" is used to make the antennas for cell phones. Have any amateurs used "fractal technology" to form their antennas? Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? Yours, JLG Heh heh....just sitting here recalling the GFW (Great Fractal War) on this newsgroup a few years ago. Where is Chip when we need him :) |
fractals and HDTV antennas
On Wed, 30 Sep 2009 00:46:28 -0400, "John Gilmer"
wrote: A month or so ago I say a PBS piece on fractals. The piece claimed that the "technology" is used to make the antennas for cell phones. Yep. The advantages of fractal antennas are small size and wide bandwidth. These are the prime requirements for cramming an antenna inside a tiny cell phone. Making it work for 800/1900Mhz cellular, 2.4GHz Bluegoof and Wi-Fi, and possibly for TV, FM, WiMax, etc, is not easy. Have any amateurs used "fractal technology" to form their antennas? Not intentionally, although many antennas (and towers) somewhat resemble a fractal, especially when they crash to the ground. Same with some "low visual impact" cell towers. To the best of my knowledge, hams are not cramming broadband radios into packages the size of cell phones. Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? Sure. So do rabbit ears, clip leads, and coat hangers. If you're in a strong signal area, almost anything will work, including a fractal antenna. However, if you're in a weak signal area, or are plagued by reflections, the more traditional designs are more useful. (Disclaimer: I've never built a fractal antenna). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
fractals and HDTV antennas
John Gilmer wrote:
Hi: A month or so ago I say a PBS piece on fractals. The piece claimed that the "technology" is used to make the antennas for cell phones. Have any amateurs used "fractal technology" to form their antennas? I recall a 10 meter fractal antenna. Strange looking thing. Disappeared some time ago from the web. It's interesting that they call fractals "technology". Any of us could generate a usable fractal, and form some wire along that pattern, and make something. "Fractal" is no more technology than is "dipole". There is a fellow who used to post here who has a company that makes such antennas. When I first came to this group, there was a war winding down. I never had any problems with the guy, but whoeeee the arguments were running hot. But on the antennas themselves, they work, but they are not a substitute for a lot of other high performance antennas. All antennas are compromises, and Fractal ones are all about getting an antenna into a small space. The are mostly UHF also. That ten meter antenna was the exception, not the rule. HF? Imagine a 160 meter Fractal. No matter how it's done, it's still going to be big. If you have a small box running at UHF, you might think about putting a fractal (or it's cousin, a small random pattern antenna) in it. But if you want to run 80 meters in a small yard, there are better ways of doing it. Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? Define work. 8^) *Real* close to the stations? then probably. As for what's inside, if there was any design at all, probably a dipole cut for the approximate frequency. But that's a guess. IMO they are a wast of money. - 73 de Mike N3LI - |
fractals and HDTV antennas
On Wed, 30 Sep 2009 09:43:33 -0700, Jeff Liebermann
wrote: Myth number one: Yep. The advantages of fractal antennas are small size and wide bandwidth. 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
On Wed, 30 Sep 2009 13:31:22 -0400, Michael Coslo
wrote: I recall a 10 meter fractal antenna. Strange looking thing. Disappeared some time ago from the web. Same page for ten years now: http://www.qsl.net/kb7qhc/antenna/fr...sket/index.htm 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
Richard Clark wrote:
On Wed, 30 Sep 2009 13:31:22 -0400, Michael Coslo wrote: I recall a 10 meter fractal antenna. Strange looking thing. Disappeared some time ago from the web. Same page for ten years now: http://www.qsl.net/kb7qhc/antenna/fr...sket/index.htm Ahh, I didn't know about your page. The one I was thinking about had an actual picture and construction ideas. So you're in the Puget Sound area? I used to stay in Poulsbo fairly often. Spent some evenings at the "Sons of Norway" club there. Coslo is a good old Norwegian name! 8^) - 73 d eMike N3LI - |
fractals and HDTV antennas
Richard Clark wrote:
On Wed, 30 Sep 2009 09:43:33 -0700, Jeff Liebermann wrote: Myth number one: Yep. The advantages of fractal antennas are small size and wide bandwidth. 73's Richard Clark, KB7QHC It's not entirely a myth -- fractal antennas can be small and have wide bandwidth. But my dummy load is small and has wide bandwidth. What makes that an "advantage"? You can take this to the bank: Small -- Broadband -- Efficient. Pick any two. Roy Lewallen, W7EL |
fractals and HDTV antennas
On Wed, 30 Sep 2009 15:26:54 -0400, Michael Coslo
wrote: So you're in the Puget Sound area? I used to stay in Poulsbo fairly often. Spent some evenings at the "Sons of Norway" club there. Coslo is a good old Norwegian name! 8^) So howcum you missed the Norwegian independance day parade here in Ballard? Largest one outside of Norway. 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
On Wed, 30 Sep 2009 15:26:54 -0400, Michael Coslo
wrote: Ahh, I didn't know about your page. No one actually cares about fractal antennas. Like the rest of the tourists, our original poster has already moved on without a second thought on the subject. The one I was thinking about had an actual picture and construction ideas. No one actually builds them either, unless they were accidentally "constructed" when left in the driveway and back over with a car. We've had actual picture of Art's antenna left on a doorstep that Art (like an unwed mother) has never acknowledged. Construction ideas litter webspace like a toilet papered tree. 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
No one actually cares about fractal antennas. Like the rest of the
tourists, our original poster has already moved on without a second thought on the subject. The one I was thinking about had an actual picture and construction ideas. No one actually builds them either, unless they were accidentally "constructed" when left in the driveway and back over with a car. We've had actual picture of Art's antenna left on a doorstep that Art (like an unwed mother) has never acknowledged. Construction ideas litter webspace like a toilet papered tree. I saw that program on PBS (I think it was Nova). They actualy interviewed the designer who used to post here all the time. Frank |
fractals and HDTV antennas
Richard Clark wrote:
On Wed, 30 Sep 2009 15:26:54 -0400, Michael Coslo wrote: So you're in the Puget Sound area? I used to stay in Poulsbo fairly often. Spent some evenings at the "Sons of Norway" club there. Coslo is a good old Norwegian name! 8^) So howcum you missed the Norwegian independance day parade here in Ballard? Largest one outside of Norway. Oh, being in PA kinda limits my access. My Sons of Norway exposure was mostly because a relative was a member. I really liked those folks though. Garrison Keillor just about has them pegged - although the folks I was around liked to party a bit more. My favorite story from those days is how when I first meet a Norwegian, they would tell you in a couple minutes if they like you or not. If they like you, they next thing they do is buy you a drink. I eventually told my father in law (the member) that we had to limit my meeting more people to the weekends, or no more than 2 an evening. - 73 de Mike N3LI - |
fractals and HDTV antennas
On Oct 1, 11:30*am, Michael Coslo wrote:
Richard Clark wrote: On Wed, 30 Sep 2009 15:26:54 -0400, Michael Coslo wrote: So you're in the Puget Sound area? I used to stay in Poulsbo fairly often. Spent some evenings at the "Sons of Norway" club there. Coslo is a good old Norwegian name! 8^) So howcum you missed the Norwegian independance day parade here in Ballard? *Largest one outside of Norway. Oh, being in PA kinda limits my access. My Sons of Norway exposure was mostly because a relative was a member. I really liked those folks though. Garrison Keillor just about has them pegged - although the folks I was around liked to party a bit more. My favorite story from those days is how when I first meet a Norwegian, they would tell you in a couple minutes if they like you or not. If they like you, they next thing they do is buy you a drink. I eventually told my father in law (the member) that we had to limit my meeting more people to the weekends, or no more than 2 an evening. * * * * - 73 de Mike N3LI - I spent 3 months in Norway, they must have liked me a lot. Good thing that happened in my youth. Jimmie |
fractals and HDTV antennas
What makes you ask? Because I want to get some help in deciding whether to buy one or not. |
fractals and HDTV antennas
On Thu, 1 Oct 2009 16:58:13 -0400, "John Gilmer"
wrote: What makes you ask? Because I want to get some help in deciding whether to buy one or not. Buy a fractal antenna? What a novel concept. Do you have an example? 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
"Richard Clark" wrote in message ... On Thu, 1 Oct 2009 16:58:13 -0400, "John Gilmer" wrote: What makes you ask? Because I want to get some help in deciding whether to buy one or not. Buy a fractal antenna? What a novel concept. Do you have an example? I saw on in a Big Box store (Target or Wally World). It said "Patented Technology." I was thinking of something for use in a high rise condo now vacent. When I lived there years ago it was possible to get about 10 or so TV stations with whatever rabbit ears that came with the TV. I have been around for awhile. I rememble a "miracle" TV antenna that was just a weight covered with plastic, for example. So I am wondering whether there is something that works like a "miracle" or are rabbit ears the state of the art for a antenna. Trouble is that with flat screen TVs, there isn't any place to put rabbit ears! |
fractals and HDTV antennas
JIMMIE wrote:
On Oct 1, 11:30 am, Michael Coslo wrote: My favorite story from those days is how when I first meet a Norwegian, they would tell you in a couple minutes if they like you or not. If they like you, they next thing they do is buy you a drink. I eventually told my father in law (the member) that we had to limit my meeting more people to the weekends, or no more than 2 an evening. - 73 de Mike N3LI - I spent 3 months in Norway, they must have liked me a lot. Good thing that happened in my youth. Yup. I know the feeling. Poulsbo had more characters per square inch than any other place I've been. I had the retired marine sargent who was afraid of ghosts - but nothing else, the most people loving person I'd ever seen, "****bird", the mumbling old gent who wasn't happy unless he had you rolling on the floor laughing, and a host of others. They were all much older than me at the time so they're probably all gone now. - 73 de Mike N3LI - |
fractals and HDTV antennas
John Gilmer wrote:
"Richard Clark" wrote in message ... On Thu, 1 Oct 2009 16:58:13 -0400, "John Gilmer" wrote: What makes you ask? Because I want to get some help in deciding whether to buy one or not. Buy a fractal antenna? What a novel concept. Do you have an example? I saw on in a Big Box store (Target or Wally World). It said "Patented Technology." I was thinking of something for use in a high rise condo now vacent. When I lived there years ago it was possible to get about 10 or so TV stations with whatever rabbit ears that came with the TV. I have been around for awhile. I rememble a "miracle" TV antenna that was just a weight covered with plastic, for example. So I am wondering whether there is something that works like a "miracle" or are rabbit ears the state of the art for a antenna. Trouble is that with flat screen TVs, there isn't any place to put rabbit ears! If you're close, try the rabbit ears. If not, try a small yagi. Fractal antennas are probably not the solution for you. One might work, but high performance is not what they are about. They are about large bandwidth in a small space. But it's the definition of small space that is the issue. - 73 de Mike N3LI - |
fractals and HDTV antennas
On Fri, 2 Oct 2009 04:03:17 -0400, "John Gilmer"
wrote: "Richard Clark" wrote in message .. . On Thu, 1 Oct 2009 16:58:13 -0400, "John Gilmer" wrote: What makes you ask? Because I want to get some help in deciding whether to buy one or not. Buy a fractal antenna? What a novel concept. Do you have an example? I saw on in a Big Box store (Target or Wally World). It said "Patented Technology." Hardly a recommendation when the technology is a corriolis force applied left hand threaded (gaussian) screw holding the maker's plaque to the merchandise. I was thinking of something for use in a high rise condo now vacent. When I lived there years ago it was possible to get about 10 or so TV stations with whatever rabbit ears that came with the TV. I have been around for awhile. I rememble a "miracle" TV antenna that was just a weight covered with plastic, for example. So I am wondering whether there is something that works like a "miracle" or are rabbit ears the state of the art for a antenna. Trouble is that with flat screen TVs, there isn't any place to put rabbit ears! Calling it fractal won't add a horizontal surface to a flat screen to sit the antenna on; and it won't remove the necessity of turning the antenna 90 degrees to catch the signal and poking you in the eye with "patented technology." Take a conventional rabbit ears antenna, lay it in the driveway, drive over it for the next of the week; and DON'T report here how well your fractal works when you put it up or you might get a cease-and-desist notice from a lawyer representing a recent Nova whore. 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
On Fri, 02 Oct 2009 10:41:46 -0400, Michael Coslo
wrote: Myth number two (or was it one?): They are about large bandwidth in a small space. 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
On Fri, 02 Oct 2009 10:34:45 -0400, Michael Coslo
wrote: "****bird" Awwww, a term of endearment that has brought tears to my eyes. 73's Richard Clark, KB7QHC |
fractals and HDTV antennas
On Sep 29, 11:46*pm, "John Gilmer" wrote:
Hi: A month or so ago I say a PBS piece on fractals. * The piece claimed that the "technology" is used to make the antennas for cell phones. Have any amateurs used "fractal technology" to form their antennas? Also, I note that "they" market HDTV antennas that are about the size of a book. * Do these things work? *What's inside them? Yours, JLG I consider any balanced symmetrical antenna a fractal. Even a dipole. What many consider as a fractal antenna, I consider a linear loaded antenna using "creative" linear loading. Is creative linear loading superior to the usual linear loading one might encounter? No one has ever proven this to be the case. They even held contests on this group to see who could build the best "fractal" antenna. It was shown that even random designs performed just as well or better than the designs offered by the local fractal guru at that time. Fractal antennas are a viable antenna to use in tight spaces, but no one has ever proven that a fractal design is any better than a random linear loading design. Not even once that I can think of. I could cover my eyeballs, and scribble out a symmetrical design on a piece of paper, and most likely it would perform just as well as a "guru" offered fractal design. A few here have proven this to be the case. What fractal antennas are really good for is when you have DOD and government contracts that require very small antennas, and need something which seems "special" in order to win these contracts. It doesn't really matter if the antennas are superior to random design linear loading. All that matters is that the ones that sign checks believe it to be the case. Kind of like the government spending $342.95 for a hammer. It doesn't matter that the expensive hammer is no better than one you can buy at Home Depot for a fraction of that price. The hype overrules the reality, and clouds the minds of those that sign checks. Needless to say, the ones that sign checks don't have a clue whether fractal antennas are worth the money or not. They could care less. They see it as redistributing wealth. :/ To me it matters not. I use manly full sized antennas, and I'll leave the little fractals to ones that want inferior performance. Heck, if I could sell boatloads of inferior antennas for boatloads of money, I could probably live with inferior antennas too. :/ I'd be laughing too hard on my way to the bank to worry about having a decent antenna for my radios. Or HDTV.. Another groaner for me. HDTV antennas.. What in the wide wide world of sports is an HDTV antenna? Do digital signals follow different rules than analog signals? Groan... Just another example of getting people to write checks for something someone claims as "special" when it's not. :( |
fractals and HDTV antennas
On Oct 2, 1:18*pm, wrote:
On Sep 29, 11:46*pm, "John Gilmer" wrote: Hi: A month or so ago I say a PBS piece on fractals. * The piece claimed that the "technology" is used to make the antennas for cell phones. Have any amateurs used "fractal technology" to form their antennas? Also, I note that "they" market HDTV antennas that are about the size of a book. * Do these things work? *What's inside them? Yours, JLG I consider any balanced symmetrical antenna a fractal. Even a dipole. What many consider as a fractal antenna, I consider a linear loaded antenna using "creative" linear loading. Is creative linear loading superior to the usual linear loading one might encounter? No one has ever proven this to be the case. They even held contests on this group to see who could build the best "fractal" antenna. It was shown that even random designs performed just as well or better than the designs offered by the local fractal guru at that time. Fractal antennas are a viable antenna to use in tight spaces, but no one has ever proven that a fractal design is any better than a random linear loading design. Not even once that I can think of. I could cover my eyeballs, and scribble out a symmetrical design on a piece of paper, and most likely it would perform just as well as a "guru" offered fractal design. A few here have proven this to be the case. What fractal antennas are really good for is when you have DOD and government contracts that require very small antennas, and need something which seems "special" in order to win these contracts. It doesn't really matter if the antennas are superior to random design linear loading. All that matters is that the ones that sign checks believe it to be the case. Kind of like the government spending $342.95 for a hammer. It doesn't matter that the expensive hammer is no better than one you can buy at Home Depot for a fraction of that price. The hype overrules the reality, and clouds the minds of those that sign checks. Needless to say, the ones that sign checks don't have a clue whether fractal antennas are worth the money or not. They could care less. They see it as redistributing wealth. :/ To me it matters not. I use manly full sized antennas, and I'll leave the little fractals to ones that want inferior performance. Heck, if I could sell boatloads of inferior antennas for boatloads of money, I could probably live with inferior antennas too. *:/ I'd be laughing too hard on my way to the bank to worry about having a decent antenna for my radios. Or HDTV.. Another groaner for me. HDTV antennas.. What in the wide wide world of sports is an HDTV antenna? Do digital signals follow different rules than analog signals? Groan... Just another example of getting people to write checks for something someone claims as "special" when it's not. *:( I remember when color TV was the rage and color was added to the name on all the TV antennas. Sometimes there was actually a stick on "color" label on the box. JImmie |
fractals and HDTV antennas
On Wed, 30 Sep 2009 00:46:28 -0400, "John Gilmer"
wrote: Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? One thing that has not been mentioned is most of the small HDTV antennas (at least the ones I have seen) include an RF amplifier. W/o the amplifier these antennas' performance is abysmal. |
fractals and HDTV antennas
What in the wide wide world of sports is an HDTV antenna? Do
digital signals follow different rules than analog signals? Groan... Just another example of getting people to write checks for something someone claims as "special" when it's not. :( I remember seeing one at CES a few years ago. An HDTV antenna, I laughed, mad at me for being too practicaal to exploit the idiot market, and remembered how in the late 60's there were suddenly "color" TV antennas. Gold anodized to make em look different. Same thing. Congratulate the guy making hte money with it. GeorgeC |
fractals and HDTV antennas
On Fri, 02 Oct 2009 16:29:19 -0400, Registered User wrote:
On Wed, 30 Sep 2009 00:46:28 -0400, "John Gilmer" wrote: Also, I note that "they" market HDTV antennas that are about the size of a book. Do these things work? What's inside them? One thing that has not been mentioned is most of the small HDTV antennas (at least the ones I have seen) include an RF amplifier. W/o the amplifier these antennas' performance is abysmal. There's an interesting twist. We're finding that these amplified gizmo's are creating problems. Too much signal for the amplifier, actually degrading performance. And they amplify the local noise, which is much of the real issue, Taiwan wall-wart supplies, etc... And they amplify FM. Combine the right two FM's and you can wipe out reception to a VHF high band TV. It is amazing how mis informed so many people are. Yeah, just ask the guy at Radio Shack. 50 years too late for that one to have a chance. GeorgeC |
fractals and HDTV antennas
There's an interesting twist. We're finding that these amplified gizmo's are creating problems. Too much signal for the amplifier, actually degrading performance. And they amplify the local noise, which is much of the real issue, Taiwan wall-wart supplies, etc... We are getting a little "thread drift" here but ... When the shift to HDTV came we suddenly found that we couldn't get reliable service for most of the channels we were used to. We live in a semi-rural place and it's over 50 miles (as the crow flies) to the nearest broadcast TV antenna. A neighbor suggested the antenna mounted amplifier (I already had a "distribution amplifier" in the basement) and it fixed us up. |
fractals and HDTV antennas
"John Gilmer" wrote in message ... There's an interesting twist. We're finding that these amplified gizmo's are creating problems. Too much signal for the amplifier, actually degrading performance. And they amplify the local noise, which is much of the real issue, Taiwan wall-wart supplies, etc... We are getting a little "thread drift" here but ... When the shift to HDTV came we suddenly found that we couldn't get reliable service for most of the channels we were used to. We live in a semi-rural place and it's over 50 miles (as the crow flies) to the nearest broadcast TV antenna. A neighbor suggested the antenna mounted amplifier (I already had a "distribution amplifier" in the basement) and it fixed us up. Mast-head amplifiers always were appropriate for 'fringe-area' reception in the old days when there were fewer transmitters around. The dynamic range issues occur closer to transmitters, of whatever type, whose signals get into the front end. If someone puts up a TETRA (or equivalent for your country) base-station near your house you might find amplifiers a lot less effective. Chris |
fractals and HDTV antennas
christofire wrote:
Mast-head amplifiers always were appropriate for 'fringe-area' reception in the old days when there were fewer transmitters around. The dynamic range issues occur closer to transmitters, of whatever type, whose signals get into the front end. If someone puts up a TETRA (or equivalent for your country) base-station near your house you might find amplifiers a lot less effective. Chris For sure. I was on the verge of returning my last analog TV because it wouldn't get one channel at all, and several others were very poor. But then I got an idea and added an attenuator at the antenna input. Problem solved -- got a great picture on all channels. The new HDTV has a better dynamic range and can put up with the strong signals, so it doesn't need the attenuator. I'm about 10 - 15 miles line of sight from urban broadcast towers. I use a commercial TV antenna in the attic. Roy Lewallen, W7EL |
fractals and HDTV antennas
J. B. Wood wrote:
In article , wrote: For sure. I was on the verge of returning my last analog TV because it wouldn't get one channel at all, and several others were very poor. But then I got an idea and added an attenuator at the antenna input. Problem solved -- got a great picture on all channels. The new HDTV has a better dynamic range and can put up with the strong signals, so it doesn't need the attenuator. I'm about 10 - 15 miles line of sight from urban broadcast towers. I use a commercial TV antenna in the attic. Roy Lewallen, W7EL Hello, Roy, and all. The trade-off here is that while putting a pad (attenuator) in front of the amplifier certainly results in a lower signal level at the amplifier output being presented to the down-stream components, the noise figure of the pad+amp cascade is increased by the attenuator loss (assuming a matched (e.g. 50 or 75 ohms)) pad. If the pad is placed at the amplifier output the noise figure is preserved but the dynamic range (usually specified in terms of a third-order intercept point) of the cascade is degraded. Noise figure and intercept points of RF distribution system amplifiers used in a shipboard environment have always been of vital interest to the USN. Sincerely, and 73s from N4GGO, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 The attenuation of an attenuator at the input of an amplifier adds directly to the noise figure (e.g., a 20 dB pad increases the noise figure by 20 dB), but the dynamic range remains the same. The dynamic range is the ratio of the largest to smallest signal a receiver can handle with acceptable performance, often defined as the ratio of the third order intercept to the noise floor, which doesn't change when you add an attenuator. For example, just picking some numbers, suppose the noise floor is -100 dBm and the intercept 0 dBm, for a dynamic range of 100 dB. Add a 20 dB attenuator to the input. Now a signal (at the input of the attenuator) of -80 dBm will be at the noise floor, and +20 dBm at the third order intercept. The dynamic range is still 100 dB, just shifted 20 dB higher. Many of the finest receivers have switchable attenuators at the front end to increase the maximum signal handling capability. In any case, there's no real alternative to an attenuator if the signal to a TV set is too large for it to handle. Roy Lewallen, W7EL |
fractals and HDTV antennas
Some book-sized efforts contain a PCB bow tie in front of a plane reflector. In others, the shapes of the elements are fiddled around with likehttp://www.instructables.com/id/How_to_make_a_fractal_antenna_for_HDT... Chris You are just asking to be sued by Nathan "Chip" Cohen, PhD. |
fractals and HDTV antennas
"Frank" wrote in message ... Some book-sized efforts contain a PCB bow tie in front of a plane reflector. In others, the shapes of the elements are fiddled around with likehttp://www.instructables.com/id/How_to_make_a_fractal_antenna_for_HDT... Chris You are just asking to be sued by Nathan "Chip" Cohen, PhD. Why's that then? Chris |
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