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If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
this was a qustion from my instractor in college
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If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"tomerbr" wrote in message oups.com... this was a qustion from my instractor in college short answer: there is no 'ideal' length. long answer: an 'ideal length' is a metaphysical concept that has no place in engineering. antennas of different lengths perform in different ways as governed by the laws of physics, obviously the designers of those antennas made some tradeoff in length vs signal strength vs distribution of energy in azimuth and elevation vs installation location and physical limitations including probably visibility, strength, produceability, and mounting method to come up with a cost effective solution to the problem of letting a user make phone calls from car. the concept of 'ideal length' assumes that there is one length that gives the best of all those possible tradeoffs which is highly unlikely to exist. |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"tomerbr" wrote in message oups.com... this was a qustion from my instractor in college As Dave said, there is no ideal length for an antenna. The 1/4 wave antenna will have a radiation patern that sends much of the signal at high angles from it. Not usually good for cell phones where they are usually on short towers (if you call a couple of hundred feet short). The longer (in wavelengths) antennas tend to put the signal more to the horizon and not overhead. By modifying the radiation patern to put it more where it is needed instead of where it is not needed you get gain in that direction and hopefully longer range. |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"Ralph Mowery" wrote in message nk.net... "tomerbr" wrote in message oups.com... this was a qustion from my instractor in college As Dave said, there is no ideal length for an antenna. The 1/4 wave antenna will have a radiation patern that sends much of the signal at high angles from it. Not usually good for cell phones where they are usually on short towers (if you call a couple of hundred feet short). The longer (in wavelengths) antennas tend to put the signal more to the horizon and not overhead. By modifying the radiation patern to put it more where it is needed instead of where it is not needed you get gain in that direction and hopefully longer range. What an absolute load of blx. The reason that car cellular antennae are longer than a 1/4 wavelength is that almost all of them are centre loaded dual antennas or are 5/8 or 7/8 co-linears. The very short ones are often a little longer as they are coupled through glass and have to be matched. The wavelength of a signal and it's aerial have nothing to do with the propagation pattern. A simple VHF or UHF folded dipole for the same mounting and wavelength related structure spacing radiates the same shape of pattern irrespective of frequency - roughly apple-shaped in cross-section. What you are getting mixed up with is the panel aerials used on most base station sites. These are almost all multiple stacked element arrays which are designed to project the signal more outwards and not down/close in, and they amost always are spaced within the package to make them directional after a fashion. Many of them have 5 deg or 10 deg of electrical downtilt to give the close-in coverage, hence why you sometimes see the 'rabbit ears' tilted backwards where range is important for that particular location. -- Woody harrogate2 at ntlworld dot com |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
On Sat, 24 Dec 2005 15:06:10 GMT, "harrogate2"
wrote: The wavelength of a signal and it's aerial have nothing to do with the propagation pattern. Nonsense! -- "What is now proved was once only imagin'd" - William Blake |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
Ralph Mowery wrote:
"tomerbr" wrote in message oups.com... this was a qustion from my instractor in college As Dave said, there is no ideal length for an antenna. The 1/4 wave antenna will have a radiation patern that sends much of the signal at high angles from it. Not usually good for cell phones where they are usually on short towers (if you call a couple of hundred feet short). A couple hundred feet is taller than most (all?) cell towers. Nextel used to boast about having the tallest towers, around 110 feet max. Sprint's towers were the shortest before Nextel bought them at around 60 feet. This is why Sprint's signal really sucked balls before Nextel bought them out. -- Paul Johnson Email and Instant Messenger (Jabber): Got jabber? http://ursine.ca/Ursine:Jabber |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
harrogate2 wrote:
"Ralph Mowery" wrote in message nk.net... "tomerbr" wrote in message groups.com... this was a qustion from my instractor in college As Dave said, there is no ideal length for an antenna. The 1/4 wave antenna will have a radiation patern that sends much of the signal at high angles from it. Not usually good for cell phones where they are usually on short towers (if you call a couple of hundred feet short). The longer (in wavelengths) antennas tend to put the signal more to the horizon and not overhead. By modifying the radiation patern to put it more where it is needed instead of where it is not needed you get gain in that direction and hopefully longer range. What an absolute load of blx. The reason that car cellular antennae are longer than a 1/4 wavelength is that almost all of them are centre loaded dual antennas or are 5/8 or 7/8 co-linears. The very short ones are often a little longer as they are coupled through glass and have to be matched. The wavelength of a signal and it's aerial have nothing to do with the propagation pattern. Wha? surely you jest! 73 de Mike KB3EIA - |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
Paul Johnson wrote:
A couple hundred feet is taller than most (all?) cell towers. Nextel used to boast about having the tallest towers, around 110 feet max. Sprint's towers were the shortest before Nextel bought them at around 60 feet. This is why Sprint's signal really sucked balls before Nextel bought them out. One of the reason they don't make them much higher is because, if they are over a certain height they have to get special permits and have to notify the FAA. -- Chris W KE5GIX Gift Giving Made Easy Get the gifts you want & give the gifts they want One stop wish list for any gift, from anywhere, for any occasion! http://thewishzone.com |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
tomerbr wrote:
this was a qustion from my instractor in college Ignore the arguing going on here and suffice it to say that you could get a PhD in antenna theory and spend a lifetime experimenting and just begin to have a clear understanding of antennas. That may be exaggerated, but only slightly. A few general things to keep in mind. Many cell phones work on two different bands, the antenna needs to work on both. When you are interested in signals in a certain direction, in this case out and not up, the longer the antenna the more gain and the more directional it will be. Don't mistake that as an indication that you just want as long as a wire as you can get, it is much more complex than that. For an omni directional antenna where you want to limit the signal to out and not up, stacking several antennas and hooking them all together in some fashion, is one way to do that, but I doubt that any of the little cell phone antennas do that. About the only time you would want an antenna that also send the signal up is if you are communicating with low earth orbit satellites that could be anywhere form the horizon to straight above you. In that case, the antennas start looking more interesting, that a vertical element. -- Chris W KE5GIX Gift Giving Made Easy Get the gifts you want & give the gifts they want One stop wish list for any gift, from anywhere, for any occasion! http://thewishzone.com |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
On 24 Dec 2005 03:15:26 -0800, "tomerbr"
wrote: If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ? this was a qustion from my instractor in college You have been sidetracked into answering the question, when the premise that "the ideal length of an antenna 1/4 wavelength" is unsupported and questionable? On what basis does your instructor make this general assertion? You could equally be trying to answer the question "If the ideal length of an antenna is 1/4 Wave length then why Medium Wave broadcast antennas commonly longer then this?" What you learn in answering the question will be useful, but you will also learn that, subject to the meaning of the term "ideal", the assertion is unfounded, it does not apply in general. It is equally valid to turn it around and ask that given so many antennas are not quarter wavelength, is quarter wavelength really ideal? Owen PS: several reasons come to mind why car cellular antennas are not quarter wave ground plane antenns, they are (over here) multi-band, they are often so-called ground independent designs (on-glass, gutter mounts etc) with elevated feed points, they seek higher gain, some are a metre long for rural coverage, they appeal to buyers who think bigger is better. -- |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
There is a simple answer, and others have given good advice:
The premis of the question is incorrect. A simple antenna such as a collinear using a quarter wave with a phasing coil and topped with another half wavelength segment will give power gain by modifying the radiation pattern. That statement should work better than OK. tomerbr wrote: this was a qustion from my instractor in college |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"tomerbr" wrote in message oups.com... this was a qustion from my instractor in college The assumption may be an error to begin with. For starters I would say a 5/8 wave antenna may be "more ideal". If you picture the radiation pattern similar to a balloon with a finite amount of water (the 'power') , the coverage of the antenna can be represented by the shape of the containment. If you press down on the balloon center with your hand then the circle of coverage will be larger - since we assume the cell towers will be on the same plane as the antenna, you can see that a flat, circular shape will cover more map area than a spherical shape would cover. A 5/8 wave antenna is but one of many types which can exhibit 'gain' by distributing the pattern in more usable directions. I suspect the antenna the Instructor is referring to is 5/8 wave, and he tried to throw you off with the 'Ideal antenna" statement. Merry Christmas |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
Do you actually have any hard data on this Paul? Not that I dont believe
you, just would like to know how many dB we are talking about. "sucked" doesnt translate very well... I was surprised when I visited the US for the first time how much higher the cell towers were compared to Australia's. From what I understand though cell use in Australia (per unit pop) topped the world for a while and it was undesirable to have high towers because the larger cell size meant co-cell interference was more likely. Towers and antennas then ended up on shorter towers and building sides to allow for the higher density of users. Towers in rural areas were of course a lot higher but they had an upper limit when you factored in the 32km limit for GSM systems. It was often frustrating when travelling in thee areas to see 3-4 cells sites in strong signal range but unable to make/receive calls because of that max distance restriction. Cheers Bob W5/VK2YQA Paul Johnson wrote: A couple hundred feet is taller than most (all?) cell towers. Nextel used to boast about having the tallest towers, around 110 feet max. Sprint's towers were the shortest before Nextel bought them at around 60 feet. This is why Sprint's signal really sucked balls before Nextel bought them out. |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
Top posting reduces readability and destroys context. It is harmful.
http://ursine.ca/Top_Posting Bob Bob wrote: Do you actually have any hard data on this Paul? Not that I dont believe you, just would like to know how many dB we are talking about. "sucked" doesnt translate very well... Alas, none that I can share except in the abstract due to nondisclosure agreements. -- Paul Johnson Email and Instant Messenger (Jabber): Got jabber? http://ursine.ca/Ursine:Jabber |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
Right you are.
Like I said - using a 5/8 wave vertical flattens out the "doughnut of propogation." And using two - back-to-back as a dipole will exhibit gain as well - over a dipole. |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"Hal Rosser" wrote:
Right you are. Like I said - using a 5/8 wave vertical flattens out the "doughnut of propogation." And using two - back-to-back as a dipole will exhibit gain as well - over a dipole. ______________ If you mean gain over a _ 1/2-wave _ dipole, then all of the single verticals 90 degrees in the plots I posted earlier (with their "image" components) already have greater peak gain than that. The peak, intrinsic gain of the 90 degree vertical and its image in my plots exactly matches the free-space peak gain of a self-resonant, 1/2-wave dipole (2.15 dBi). The fact that all of the radiation from these verticals is confined to a 1/2 hemisphere adds 3 dB h-plane gain to all of the plots. RF |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
Just to start an argument, why is it that EZNEC shows zero gain for a
vertical antenna in the horizontal plane? Whereas, all your diagrams show maximum gain along the horizontal. ---- Reg. |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"Richard Fry"
... confined to a 1/2 hemisphere adds 3 dB h-plane gain to all of the plots. ______________ Sorry, delete the "1/2" in my statement above. My bad. RF |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"Reg Edwards" wrote
Just to start an argument, why is it that EZNEC shows zero gain for a vertical antenna in the horizontal plane? Whereas, all your diagrams show maximum gain along the horizontal. ____________ EZNEC shows the same patterns/gains as in the plots I posted, when its models are set up correctly. RF |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
Reg Edwards wrote:
Just to start an argument, why is it that EZNEC shows zero gain for a vertical antenna in the horizontal plane? Whereas, all your diagrams show maximum gain along the horizontal. Sometimes the maximum gain is zero dBi? -- 73, Cecil http://www.qsl.net/w5dxp |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"Richard Fry" wrote "Reg Edwards" wrote Just to start an argument, why is it that EZNEC shows zero gain for a vertical antenna in the horizontal plane? Whereas, all your diagrams show maximum gain along the horizontal. ____________ EZNEC shows the same patterns/gains as in the plots I posted, when its models are set up correctly. RF ======================================== The model for a simple vertical above ground is simple enough. Perhaps YOUR way is incorrect if the pattern disagrees so strongly with EZNEC. ---- Reg. |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"Reg Edwards" wrote
"Richard Fry" wrote "Reg Edwards" wrote Just to start an argument, why is it that EZNEC shows zero gain for a vertical antenna in the horizontal plane? Whereas, all your diagrams show maximum gain along the horizontal. ____________ EZNEC shows the same patterns/gains as in the plots I posted, when its models are set up correctly. RF ======================================== The model for a simple vertical above ground is simple enough. Perhaps YOUR way is incorrect if the pattern disagrees so strongly with EZNEC. ---- Reg. _______________ Reg, My models agree with theory and measured results, as have been developed and well-proven for 60+ years in the broadcast industry. If you doubt my plots, why not send them to Roy Lewallen ask for his comments? You might also ask him to tell you how to model these configurations properly using EZNEC. I'd explain it, but probably that wouldn't be acceptable to you (plus you didn't ask me). RF |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
Reg Edwards wrote:
Just to start an argument, Things are even duller than usual in Rowley Regis, I see. why is it that EZNEC shows zero gain for a vertical antenna in the horizontal plane? Whereas, all your diagrams show maximum gain along the horizontal. C'mon Reg, it's only been three months since you last asked this and got it answered(1). The time before that was four years earlier(2), and before that multiple times going back at least to 1998(3). At the rate you're going, you'll be asking it weekly before long. Getting tired of promoting "TLI"s, grumping at "Gurus" (while carefully excluding yourself, of course), grousing about Americans, and asking "Who's Kraus"? C'mon, be original. Surely you can think of a new topic to keep you awake on those long, boring evenings. I've got an idea -- maybe you can use your knowledge to actually help some of the folks who ask serious questions on this newsgroup. For anyone who wants an answer to Reg's perennial question, use groups.google.com to look up the following threads on this newsgroup, where Reg has asked the same question and where it's been answered: (1) "best HF antenna system next to a trailer?", Sept. 2005 (2) "40M Delta Loop Advice Needed:", May 2001 (3) "Raised V's burried ground systems." [sic], Feb. 2000 "Ground Radial system comparisons", April 1999 "Is there", Aug. 1998 "Better for DXing: Beam or vertical?", Aug. 1998 Roy Lewallen, W7EL |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
Roy, you'll just have to accept the fact that I'm peculiar. But no
more peculiar than other frequenters of this newsgroup. I don't think I do much damage. ---- Reg. |
If the ideal lenght of an antenna is 1/4 Wave lenght then wayare the Car Cellular antennas are longer then this ?
Reg Edwards wrote:
Roy, you'll just have to accept the fact that I'm peculiar. But no more peculiar than other frequenters of this newsgroup. How's this for peculiar? :-) "The movement of energy within the line is complex; in the abbreviated analysis I've had time to do so far, it sloshes back and forth in regions within the line." -- 73, Cecil http://www.qsl.net/w5dxp |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
Richard, I thank you for your time and trouble expended in trying to educate me regarding the field strength from a 1 Kw transmitter at a distance of 1 Km. Your efforts, of course, will not be wasted on other readers of this newsgroup. Very good stuff! But you have misunderstood my attitude towards this discussion. As I have said before, amateurs and professionals alike, all suffer from delusions of accuracy. The uncertainty in prediction of field strength of groundwaves can amount to 10 or 15 dB or even more at extreme distances. When I say my program correctly predicts a field strength of 300 millivolts per metre at a distance of 1 Km from a 1 Kw transmitter, nobody can disprove it. Even the 'bibles' state it as a matter of fact. But we all know how much faith can be placed in 'bibles'. To be of use, all measurements should be associated with an uncertainty. Only then can the originators be judged to understand what they are waffling about. Thank you for your interest. ---- Reg, G4FGQ. |
If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ?
"Reg Edwards"
When I say my program correctly predicts a field strength of 300 millivolts per metre at a distance of 1 Km from a 1 Kw transmitter, nobody can disprove it. Even the 'bibles' state it as a matter of fact. But we all know how much faith can be placed in 'bibles'. To be of use, all measurements should be associated with an uncertainty. Only then can the originators be judged to understand what they are waffling about. ______________ Interesting point of view, Reg. The correct application of physical laws disproves your contention, and the equations that do it are not difficult. Here they a E = SQRT(49.2*P)/D where E = Peak inverse (free-space) field from a self-resonant, 1/2-wave dipole (volts/meter) D = Distance (meters) As radiation from a vertical antenna with its base at ground level is confined to one hemisphere, field strength at that distance over a perfect, infinite, flat "ground" plane is E * SQRT(2). This generates the value of the maximum possible field from a perfect 1/4-wave vertical radiator over a perfect ground plane, which has been proven and used for many decades in the broadcast industry. This is the groundwave field that then is subject to various propagation losses related to earth conductivity, diffraction etc over long paths, once the radiation has been launched. N.B. -- at a distance of 1 km, such losses are negligible for the typical broadcast vertical with its 120 buried radials, regardless of ground conductivity. Why not use the formulae in your program that actually generates the correct value, instead of just saying it does, or implying that your approach is "good enough?" RF |
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