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"Roy Lewallen" wrote in message ... "Takeoff angle" can have two meanings. The first, and really a misuse of the term, is the one used by antenna modeling programs such as EZNEC. It means the elevation angle at which an antenna's radiation is maximum. This is a property of the antenna and its local environment (particularly the height above ground for horizontal antennas, and local ground quality for vertical antennas). And I thank very much for the above statement to which I fully agree. But later you turn away from that statement with respect to the propagation conditions do you not? The second meaning is the elevation angle at which propagation occurs. This is dictated mainly by the propagation path -- the distance and the effective height of the ionosphere. The antenna pattern can play a role only when more than one path is possible, for example single and double hop, by modifying the amount which propagates by each path.he environment Now Roy I have a problem with what you are saying here I spend hours modelling an array to lower the TOA or angle of max radiation which directly controls the main lobe dimension both in width and height. I model an antenna array such that it emulates in a way a "stacked" array where as low as a 9/10 degree TOA. The 3 db gain window is broader in width and narrower in height than say the normal array. It is this "TOA" that determines what window we have and where it hits the ionesphere which thus determines its point of arrival on the earths surface Not propagation which is the "environment" of all antenners in the vicinity and the same for all antennas at a particular time. The ARRL clearly shows that it is the TOA that determines the range as it were of one antenna comparered to the others with different TOA.. For the life of me I cannot concurr with the statement as stated. I would also add that a antenna with a lower TOA invarably means a thinner lobe of radiation as well as a lower 3dB window and in a few cases the underside contour of the main lobe can be lower than one of equivalent gain. I use the term TOA as being the line of maximum gain In no way do I infer that we have laser type radiation as compared with a flashlight style radiation The "takeoff angle" of the first meaning (angle at which the radiaion is maximum) isn't a particularly useful measure of and antenna's performance, and it certainly doesn't determine the real "takeoff angle" of the second meaning (angle at which propagation occurs). Then it is here that that we are entangled. I agree the envionment can affect or deflect radiation, whether it be a mountain face or the down slope of a mountain, but I do not see how existing propagation can mold the direction of such radiation, and possibly it is here that my learning curve can be bettered . To me, propagation affects first come into being when the ionesphere is able to" turn" or "deflect" radiation according to the relative angle of impact of that which it turns and not before. ( when all is said and done this is the crux of the debate) Art has used "takeoff angle" of the first meaning liberally in his writings, often with the added and incorrect implication that all the radiation from an antenna occurs at its "takeoff angle", with none at other elevation angles. So his confusion about Richard's statement (which correctly used "takeoff angle" in the second sense) is understandable. No, That is not true. My experimentation is aimed at arriving at a low TOA for an antenna. The reason is two fold "1" A lower TOA usually means that the upper half of the main lobe is reduced and the lower half of the lobe is not reduced. Thus radiation is contained within an angle of radiation that is usefull and not wasted as it is with an antenna of a higher TOA. "2" When the attributes of "1" above are achieved it is then possible to LOWER the underside of the main lobe contour where one can communicate at lower angles with a single feed array and obtain the advantages of multi stacked arrays with multi feed point. Is this the error of my ways where any change I make to an antennas pattern is rendered of no use because I must first find a way to manipulate propagation where all the action is really at? I also want to make it clear that I appreciate your post which I see as an attempt to clarify matters that are presently being discussed ie.It is propagation and not the antenna that determines the TOA. Or "antenna pattern is determined by propagation" so that we don't get hung up on the term TOA Very best regards Art Roy Lewallen, W7EL wrote: Richard, You are at it again, avoiding the supply of corroberation to what you say is true. Stick to the basic statement that you made, which from their silence, the gurus concur with. Your statement was that: propagation is what determines TOA and I ask for confirmation of the correctness of that statement from you in the nature of some written text. The gurus obviously accept your statement as fact, but I do not. Usually you refer to a text to back up your statement ,but this time you haven't, winging it and relying solely on the fact that the gurus agree with you. Surely you or some guru can come up with a written text that states that propagation is what determine TOA.! That is what this group is all about where gurus debunk the untruths and supply the real truths and not to let old wives tale dominate. You also stated that you made the ":assumption" presumably based on the "facts" stated above that the Curtain could be considered as similar to the dipole since propagation determines that they are the same. This is total junk ,in its entirety, unless you or the gurus can come up with a written text that confirmes their positions. Art |
On Tue, 26 Apr 2005 08:16:56 +0100, Ian White GM3SEK
wrote: -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3s So you've finally emigrated Ian! Good luck in the move.. Peter, G3PHO |
O.K. Richard I'll leave it at that with you . You continue to send
prewritten responses to questions that were not asked.or do not pertain to the subject at hand I will leave it to you to alert all antenna labs not to test antennas when there is no propagation or, failing that, leave a bucket under the antenna to compensate for the lack of TOA or elevation angle because of the lack of propagation generated modifying actions.. I don't know that if they leave the door open during testing it will suffice. You can always supply a written technical text to justify youir actions when you find it. Nuf said Art "Richard Harrison" wrote in message ... Art Unwin wrote: "Surely you or some guru can come up with written text that states that propagation is what determines TOA." I don`t find TOA in any index. I find "elevation angle", which I suppose is a synonym, in my 19th edition of The ARRL Antenna Book. On page 2-9 it says: "The elevation angle is referenced to the horizon at the earth`s surface , where the elevation angle is 0-degrees." On page 3-5, the same book says: "Now look at Fig. 4A, which compares the computed vertical-angle response for two half-wave dipoles at 14 MHz." The Antenna Book is not very definitive. "Transmission Lines, Antennas, and Wave Guides" on page 314 says: In order to escape from the earth without excessive ground attenuation, a sky wave must leave the earth at an angle of at least 3-degrees above the horizon.---At 3-degrees elevation, the distance per hop is about 3,500 km (2,100 miles). Longer distances are automatically broken up into units not exceeding 3.500 knm." It`s the medium breaking up the hops, not the antenna. Best regards, Richard Harrison, KB5WZI |
On Tue, 26 Apr 2005 19:59:59 +0000 (UTC), "Reg Edwards"
wrote: But for the two figures to be of value the uncertainties in the determination should be stated on the certificate (a legal document). What are TYPICAL uncertainties, in dB, which appear above the Head of the Laboratory's signature. Hi Reg, I thought Wes' link was quite specific to the matter: Measurement Mismatch Correction Error 0.04 Noise Power of Power Sensor 0.00 Zero error of Power Sensor 0.00 Power Meter Linearity 0.04 Space Loss Measurement Error 0.01 Multipath Curve Fitting Random Error 0.04 Proximity Effect Correction Error 0.05 All expressed in dB and may be combined using the usual methods of RMS, RSS, or worst case simple sum. 73's Richard Clark, KB7QHC |
Peter wrote:
So you've finally emigrated Ian! Still commuting, but G3SEK is definitely QRT so I changed the signature. I'm hoping to get on the air from GM next week. Web URLs will still be "g3sek" but e-mail to either will be OK. Good luck in the move.. Thanks, I'll keep those good wishes in my back pocket! -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
"Roy Lewallen" wrote in message ... wrote: . . . Now Roy I have a problem with what you are saying here I spend hours modelling an array to lower the TOA or angle of max radiation which directly controls the main lobe dimension both in width and height. And, as I've said quite a few times in one way or another, it's largely a waste of time. Why? A single word question On what authority do you base that statement on? I model an antenna array such that it emulates in a way a "stacked" array where as low as a 9/10 degree TOA. The 3 db gain window is broader in width and narrower in height than say the normal array. It is this "TOA" that determines what window we have and where it hits the ionesphere which thus determines its point of arrival on the earths surface That's absolutely incorrect. All antennas radiate at all angles. The ionosphere doesn't know or care at what angle your antenna is radiating the most -- propagation will occur at the angle favored by the ionosphere at the time. Your antenna's pattern doesn't dictate the geometry of the path. Not propagation which is the "environment" of all antenners in the vicinity and the same for all antennas at a particular time. The ARRL clearly shows that it is the TOA that determines the range as it were of one antenna comparered to the others with different TOA.. For the life of me I cannot concurr with the statement as stated. By speaking of "environment" I was not including propagation, and in conforming to traditional usage, I also don't include propagation when speaking of antenna patterns. An antenna pattern is a polar plot of the field intensity of the antenna at a distant point, but with the assumption that the propagation to all points is lossless. The actual signal received at a distant point requires the inclusion of propagation effects. The pattern is one element in the equation, but only one. . . . Is this the error of my ways where any change I make to an antennas pattern is rendered of no use because I must first find a way to manipulate propagation where all the action is really at? . . . Close. Sometimes two or more propagation modes are possible, such as single and double hop. From here to say, New York, I might have single hop at 3 degrees and double hop at 12. (Please forgive me if those particular propagation angles can't really occur at the same time, but they're in the ballpark.) It doesn't matter one iota what the angle of maximum radiation from my antenna is. All that matters is the gain or field strength at elevation angles of 3 and 12 degrees. All the rest of the radiation will go some place besides New York. As a general rule, I can get a stronger signal to New York with X dBi at 3 degrees than the same gain at 12, because the single hop path loss is usually less. So it might pay me to maximize my gain at that angle at the expense of 12 degrees. On the other hand, the other station's antenna pattern is just as important -- if it has a lot more gain at 12 degrees than 3, he might not hear me if I put out most of my energy at 3 rather than 12. But in any case, it doesn't matter how much I'm radiating at 1, 5, 7, or 15 degrees, or what my antenna's maximum angle is. All that counts is how much I'm radiating at 3 or 12 degrees. Other than manipulating your antenna to radiate more or less at those two angles, you don't get to "manipulate propagation" to support other angles at a given time, frequency, and path. You're stuck with those until the ionosphere changes. Knowledgeable DXers (which I'm not) spend a lot of time working out what the angles will be for propagation to various target locations, and how to design, build, and switch antennas to maximize the amount of radiation at those angles. I also want to make it clear that I appreciate your post which I see as an attempt to clarify matters that are presently being discussed ie.It is propagation and not the antenna that determines the TOA. Or "antenna pattern is determined by propagation" so that we don't get hung up on the term TOA No, antenna pattern isn't determined by propagation. Whoopee The signal strength at the other end of the path is determined by the gains of both the transmit and receive antennas at the elevation angle of propagation, and the loss along the path. Period. Notice that "takeoff angle" and "pattern" didn't appear in that sentence. And you don't get to choose the angle of propagation (unless more than one are supported at a given time, which is only sometimes true, and then you can only choose between the supported angles). It is up to the user to design the antenna with the pattern of choice and that is what I did. And you can do it to since you are familiar with antenna programs. You just have to point the initial program so it is able to spot what dimensions are required to produce the required pattern. Roy please go back to the top and answer that simple one word question and let it all hang out Best regards Art I suggest downloading the excellent, free, and easy to use propagation software by Shel Shallon, W6EL, http://www.qsl.net/w6elprop/. In a few minutes, you'll be able to see what angles are supported at a given time and frequency for a given path. Roy Lewallen, W7EL |
Richard, why don't you just say that the angle of elevation of the
radio path has nothing whatsoever to do with the type of transmitting and receiving antennas, or the directions in which they may be pointing or elevated, or even the operating frequency. When communication has been established between A and B, the angle of elevation depends only on the locations of A and B on the Earth's surface, on the number of hops, on the height of the ionospheric layers, and on the slope of the layers. The elevation angle is determined purely by trigonometry. It tends to be the same at both A and B. There may be simultaneously more than one path and therefore more than one angle. In which case multi-path distortion and fading occurs. Received signal strength depends on the two antenna gains in the direction of the path. The take-off angle predicted by Eznec-type programs is an altogether different thing. It depends on reflections from the ground in the vicinity of the two antennas. It does however have an effect on received signal strength but is of use only when the locations of A and B and all other geographic and ionospheric variables are known. They seldom are! As are ground conditions. ---- Reg, G4FGQ. |
Richard, I can agree with that
Wes obviously paid close attention to Reggies initial post and replied in a way that was very informativeI and reflected his knoweledge in that particular field Nobody else came even close to identifying Reggies needs and responded in such a professional manner. He should be congratulated Regards Art "Richard Clark" wrote in message ... On Tue, 26 Apr 2005 19:59:59 +0000 (UTC), "Reg Edwards" wrote: But for the two figures to be of value the uncertainties in the determination should be stated on the certificate (a legal document). What are TYPICAL uncertainties, in dB, which appear above the Head of the Laboratory's signature. Hi Reg, I thought Wes' link was quite specific to the matter: Measurement Mismatch Correction Error 0.04 Noise Power of Power Sensor 0.00 Zero error of Power Sensor 0.00 Power Meter Linearity 0.04 Space Loss Measurement Error 0.01 Multipath Curve Fitting Random Error 0.04 Proximity Effect Correction Error 0.05 All expressed in dB and may be combined using the usual methods of RMS, RSS, or worst case simple sum. 73's Richard Clark, KB7QHC |
Art, propagation does indeed determine the takeoff angle. Let's call that
pTOA. An antenna also has a design takeoff angle. We will call that aTOA. I think you may be using the term applied to an antenna, Don't confuse it with pTOA. two different animals with the same name. " wrote in message news:zgube.16975$c24.6191@attbi_s72... Richard, You are at it again, avoiding the supply of corroberation to what you say is true. Stick to the basic statement that you made, which from their silence, the gurus concur with. Your statement was that: propagation is what determines TOA and I ask for confirmation of the correctness of that statement from you in the nature of some written text. The gurus obviously accept your statement as fact, but I do not. Usually you refer to a text to back up your statement ,but this time you haven't, winging it and relying solely on the fact that the gurus agree with you. Surely you or some guru can come up with a written text that states that propagation is what determine TOA.! That is what this group is all about where gurus debunk the untruths and supply the real truths and not to let old wives tale dominate. You also stated that you made the ":assumption" presumably based on the "facts" stated above that the Curtain could be considered as similar to the dipole since propagation determines that they are the same. This is total junk ,in its entirety, unless you or the gurus can come up with a written text that confirmes their positions. Art "Richard Harrison" wrote in message ... Art Unwin wrote: "---may I go back to the "compared to a dipole" statement which Richard keeps brushing off." I accept a resonant dipole reference as a given. It is true that the antenna under test and the reference dipole have different radiation patterns. Our goal was to compare received signal strengths at locations of interest. The assumption was that on average, the propaqgation was nearly the same for the signals received from both transmitting antennas. Good or bad propagation, the difference between the signals depended on gain in the direction of the receiver as the transmitted power was the same to both antennas no matter where it landed. Kraus says on page 535 of his 3rd edition of "antennas": "Suppose that we express the gain with respect to a single lambda/2 element as the reference antenna. Let the same power P be supplied to this antenna. Then assuming no heat losses, the current Io is the sq rt of the power divided by the resistance of the reference antenna. In general, the gain in field intensity of an array over a reference antenna is given by the ratio of the field intensity from the array to the field intensity from the reference antenna when both are supplied with the same power P." Kraus` example was our intended case. Our expectations were met and our contractors were paid. Best regards, Richard Harrison, KB5WZI |
Richard Clark wrote:
Hi All, The method described by the paper offered above is a commonplace of Metrology called "Reciprocity." I have calibrated precision microphones against this method, and the error math offered is consistent with my experience (much less the actual values offered as examples). Any references on microphone calibration? Maybe a short tutorial? That is something I have a need to do. tom K0TAR |
"Roy Lewallen" wrote in message ... wrote: . . . Now Roy I have a problem with what you are saying here I spend hours modelling an array to lower the TOA or angle of max radiation which directly controls the main lobe dimension both in width and height. And, as I've said quite a few times in one way or another, it's largely a waste of time. O.K. Roy let's get down to the nitty gritty and look at this question. Your background in antenna programs makes you a person of choice to declare if what I do is a waste of time and where I must default to an experts judgement. A month or so ago I gave a description of the antenna that I modelled and for your interest I used the AOP program by Beasely a person that you have collaborated with in the past. One can design a yagi antenna with 8 elements say on a 60 foot boom and then note the gain and the elevation angle of maximum gain. This can be done using the most basic antenna program available. The next step is to apply this same antenna to a program that is capable of changing dimensions to obtain a desired function ,which in this case can be "Gain". There is reference to a NEC program on this group during the past week or so that I believe is capable of doing this, that is on the web and also free to all. With the use of variable dimensions which includes best x,y and Z positions for various pulses or physical positions the program will procede to do as asked. This test is about as simple as it gets to show how the angle of max radiation can be changed as well as the envelope of the new angle range to achieve a 3 dB window of radiation You will see that the computor program will immediately remove itself from a Yagi design to obtain a better gain and form an array that consists of one driven element and where the rest are all reflectors! Though the final shape appears to represent a dish it is not, it is simply a design with multiple dimentional reflectors in the best coupling mode. The result is a gain figure that will exceed the original design, which is what we requested of the program i.e.allow it to make changes of choice to achieve a higher gain than the initial yagi design With the above. one can change the elevation angle for maximum gain which has now dropped to a 11 to 10 degrees or even 9 degrees if one is willing to sacrifice some gain. This can be also be achieved by allowing the driven element to deviate from a straight dipole to a vee shape tipped in such away to helps control reactance swings of the total array. The above is quite simple to duplicate, where anybody can place a 8 element yagi with a long boom of 60 ft placed over real ground and challenge the program to devise a way of increasing gain. In my case the program changes to a non director mode without any prodding, other programs may well need some prodding. Changes to elevation for maximum gain will change automatically and one can expect to easily devise an array with a 10 degree angle where a gain of 16 dbi is attained as well as a broader lobe than can not be accomplished with a Yagi design. If you find that you cannot repeat the above results in a short space of time then it surely reflects a misuse of programs on my part. Please note that propagation has no part in forming the shape of the main lobe to the best of my understanding but you would know better than most as to what the program parameters actually are I look forward to your response or any other program users response that shows my findings are a waste of time so I can direct my experimentation in a more fruitfull direction. Best regards Art I model an antenna array such that it emulates in a way a "stacked" array where as low as a 9/10 degree TOA. The 3 db gain window is broader in width and narrower in height than say the normal array. It is this "TOA" that determines what window we have and where it hits the ionesphere which thus determines its point of arrival on the earths surface snip Is this the error of my ways where any change I make to an antennas pattern is rendered of no use because I must first find a way to manipulate propagation where all the action is really at? . . . Close. Sometimes two or more propagation modes are possible, such as snip any case, it doesn't matter how much I'm radiating at 1, 5, 7, or 15 degrees, or what my antenna's maximum angle is. All that counts is how much I'm radiating at 3 or 12 degrees. Snip I also want to make it clear that I appreciate your post which I see as an attempt to clarify matters that are presently being discussed ie.It is propagation and not the antenna that determines the TOA. Or "antenna pattern is determined by propagation" so that we don't get hung up on the term TOA snip I suggest downloading the excellent, free, and easy to use propagation software by Shel Shallon, W6EL, http://www.qsl.net/w6elprop/. In a few minutes, you'll be able to see what angles are supported at a given time and frequency for a given path. Best regards Art Roy Lewallen, W7EL |
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Roy Lewallen wrote:
Close. Sometimes two or more propagation modes are possible, such as single and double hop. From here to say, New York, I might have single hop at 3 degrees and double hop at 12. (Please forgive me if those particular propagation angles can't really occur at the same time, but they're in the ballpark.) It doesn't matter one iota what the angle of maximum radiation from my antenna is. All that matters is the gain or field strength at elevation angles of 3 and 12 degrees. All the rest of the radiation will go some place besides New York. As a general rule, I can get a stronger signal to New York with X dBi at 3 degrees than the same gain at 12, because the single hop path loss is usually less. So it might pay me to maximize my gain at that angle at the expense of 12 degrees. On the other hand, the other station's antenna pattern is just as important -- if it has a lot more gain at 12 degrees than 3, he might not hear me if I put out most of my energy at 3 rather than 12. But in any case, it doesn't matter how much I'm radiating at 1, 5, 7, or 15 degrees, or what my antenna's maximum angle is. All that counts is how much I'm radiating at 3 or 12 degrees. Other than manipulating your antenna to radiate more or less at those two angles, you don't get to "manipulate propagation" to support other angles at a given time, frequency, and path. You're stuck with those until the ionosphere changes. Knowledgeable DXers (which I'm not) spend a lot of time working out what the angles will be for propagation to various target locations, and how to design, build, and switch antennas to maximize the amount of radiation at those angles. snip Roy Lewallen, W7EL Roy The Canadian with 2 calls, VE3GK/VE2GK, Gerry King, made a very nice 20 meter antenna system, which he gave a great talk about at our local hamfest in northern NY back around 1978 +-. This system was unique, at least then, in that he had 2 20 meter beams that could be used singly, upper or lower, or as a stack, and could independently vary their heights. He reported very good success, since he could vary the angle of greatest radiation at will. He is now a silent key, unfortunately, but his site is still up. I will leave it to those interested to find it, it's not hard, but his heirs don't need useless traffic. I am not sure if his old system is pictured on the page. tom K0TAR |
Reg, G4FGQ wrote:
"Richard, why don`t you just say that the angle of elevation of the radio path has nothing whatsoever to do with the type of transmitting and receiving antennas or the directions in which they may be pointing or elevated, or even the operating frequency." Confuse the readers? Geometry and trigonometry are involved. What`s more, the signal may take more than one path between only two points, or multiple hops, or multiple azimuths. This causes fading and distortion. Transmitted energy in directions other than to a receiver is wasted. That`s one of several reasons to use antenna directivity in azimuth and elevation. Maybe Cecil`s IEEE Dictionary defines TOA. The references I`ve found are to "elevation angle" above the horizon. In general, an antenna`s angle of maximum response is lowered by raising the antenna height. If you have stacked horizontal elements you can adjust their phasing to skew the elevation angle up or down some. An ideal HF antenna may be a giant array of dishes that might be aimed for one-hop, if possible, in a multiple diversity system. Something almost as good is a triple diversity system which uses rhombics. 3 receiving rhombics are plavced with about 10-wavelengths of lateral spacing at the lowest frequency received. Multicouplers on each rhombic feed various receivers , often at various frequencies. Diversity combiners select the best received signal of three carrying the same program. The results are spectacular. We used such TDR systems for broadcast program relay. Often the quality was as if the program arrived by cable. Best regards, Richard Harrison, KB5WZI |
Richard Clark says -
Hi Reg, I thought Wes' link was quite specific to the matter: ===================================== Hi Richard, I originally wrote - "Does anyone have typical examples of measurement uncertainties claimed by antenna testing stations? Answers in decibels please." The two links to papers, kindly found by Wes, are both devoted to microwave horns and dishes. Very interesting and directly related to the subject. But in anticipation of the sort of replies I would receive, and in fact did receive, I specifically asked - "A reply from a testing station, at HF or VHF, would be specially appreciated." It appears that at microwaves a worst-case uncertainty of 0.2 dB, that is a range of nearly half dB, is achievable in the National Physical Laboratory at Teddington on Thames, London. Which is a little hard for an Old Timer like me to believe. But at HF and VHF, at which amateurs are mostly interested, the uncertainty on a typical open-air range is sure to be greater. If only because great accuracy of rocket technology at the lower frequencies is not needed. It nearly always occurs that technical enquries at LF and HF get lost in the elevated mysteries of microwaves, circulators and scattering-parameters. I am unfamiliar with precision antenna test and measurement methods. I don't particularly wish to know. But if you, as an employee of a reputable laboratory, were given the job of determining the forward and reverse gains of fractal or other weird antennas, at 7 MHz and 144 MHz, what uncertainties would you state? I'd believe you. ---- Reg, G4FGQ. |
On Tue, 26 Apr 2005 19:15:44 -0700, Roy Lewallen
wrote: wrote: "Roy Lewallen" wrote in message ... wrote: . . . Now Roy I have a problem with what you are saying here I spend hours modelling an array to lower the TOA or angle of max radiation which directly controls the main lobe dimension both in width and height. And, as I've said quite a few times in one way or another, it's largely a waste of time. Why? A single word question On what authority do you base that statement on? Because "takeoff angle" as you use the term does not bear a direct relationship to the ability to communicate. Right on. Let's look at it this way. If I have an antenna with a "pencil beam" and it's pointing at 90 degree azimuth and the station I want to communicate with is at 0 degrees, I don't know of anyone who would say that this is an optimum situation. Yet, many (okay, one) would say that an antenna with (pardon me) a "take off angle" of 3 degrees is *always* superior to one with a TOA of 20 degrees, notwithstanding the fact that the desired station's signal is maximum at 20 degrees. This is like saying that I have room for a rhombic pointed at Asia so I'm going to work my ass off optimizing it when all of the stations I want to work are in Europe. Why is this so? I'm completely baffled. |
"Roy Lewallen" wrote in message ... wrote: "Roy Lewallen" wrote in message ... wrote: . . . Now Roy I have a problem with what you are saying here I spend hours modelling an array to lower the TOA or angle of max radiation which directly controls the main lobe dimension both in width and height. And, as I've said quite a few times in one way or another, it's largely a waste of time. Why? A single word question On what authority do you base that statement on? Because "takeoff angle" as you use the term does not bear a direct relationship to the ability to communicate. O.K. Roy if you are going to let this discussion revolve solely around the term of TOA which is a datum line around which the main lobe evolves,, A term you have voiced opposition to over the years and which you personally use in your own antenna program design then you will be succesfull in any debate regarding antennas. I have stated many times that the elevation angle denotes the line of maximum gain and the lobe that surrounds this angle denotes the area of communication ability represented by the oft used term of the 3 dB window. You are refusing to accept the use of this term because of personal emotional reasons, that you only use the term under protest because of commercial reasons and now as a basis for rejecting. new knoweledge supplied by computor programs.,. presumably by clinging to "all is known" mantra I will never persuade you to view this thread with an open mind. You have stated that TOA as I describe the term does not bear a direct "relationship " to the ability to communicate which obviously must relate to a part of a post where you envision that you have accomplished a "gottcha". One person stated that everybody knows that I am right which I question, especially since you have now come forward with contrary thoughts. Roy, there can be no debate if one must always accept all your statements in Pope like fashion that excludes discussion. Best regards Art Roy Lewallen, W7EL |
Richard Harrison wrote:
Maybe Cecil`s IEEE Dictionary defines TOA. The references I`ve found are to "elevation angle" above the horizon. Nope, none of my references mentions TOA. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
I believe "takeoff angle" is in the same category as "capture area" and
"S-unit" -- terms which nobody except amateurs seem to need. Roy Lewallen, W7EL Cecil Moore wrote: Richard Harrison wrote: Maybe Cecil`s IEEE Dictionary defines TOA. The references I`ve found are to "elevation angle" above the horizon. Nope, none of my references mentions TOA. -- 73, Cecil http://www.qsl.net/w5dxp |
wrote:
. . . You are refusing to accept the use of this term because of personal emotional reasons, that you only use the term under protest because of commercial reasons and now as a basis for rejecting. new knoweledge supplied by computor programs.,. presumably by clinging to "all is known" mantra I will never persuade you to view this thread with an open mind. . . . Roy, there can be no debate if one must always accept all your statements in Pope like fashion that excludes discussion. Best regards This sort of response doesn't constitute a debate, and it's nothing I see any need or desire to respond to. Roy Lewallen, W7EL |
No that is not what it is all about. Some here object to the term of TOA and
want strict adherence to the description in terms of "elevation angle". This same subject came up a few months ago and went on for a long time. Now we are at it again and allowing the discussion to supplant original thoughts. You can now see that somebody has inventing a statement in straw man fashion and then using the lie as a truthful fact for the basis of an illicit attack. Anything goes I'll wager if you look up the thread of a few months ago on a TOA thread you will see contrary postings by the same persons that are posting now, this purely for the sake of a continueing augument. This group will never agree to anything other than all is known about antennas and will fight to the death if anybody alludes to anything that conflicts with this. It is for that reason the debate has been throttled and why TOA as shown in some computor programs is used as a diversionary tactic. I give up ! The world is flat. I will not disagree with that statement anymore so that emotions can now settle down and I can live in peace In addition: All is really known about antennas since there is no evidence of a scientific book that has been written about what is unknown about antennas. In addition : I urge all newcomers to the hobby to accept the notion that propagation can modify radiation immediately after emmission from a radiating antenna , this being a consensus of viewa by noted Gurus in the hobby In addition If a commercial computor program uses the term of TOA then it is not to be trusted aince it is based around terms that are known to be invalid and it must be left to the user to determine how far this invalidity extends with respect to results obtained. Many commercial programs use this same term so it is a case of buyer beware. Best regards Art "Fred W4JLE" wrote in message ... Art, propagation does indeed determine the takeoff angle. Let's call that pTOA. An antenna also has a design takeoff angle. We will call that aTOA. I think you may be using the term applied to an antenna, Don't confuse it with pTOA. two different animals with the same name. " wrote in message news:zgube.16975$c24.6191@attbi_s72... Richard, You are at it again, avoiding the supply of corroberation to what you say is true. Stick to the basic statement that you made, which from their silence, the gurus concur with. Your statement was that: propagation is what determines TOA and I ask for confirmation of the correctness of that statement from you in the nature of some written text. The gurus obviously accept your statement as fact, but I do not. Usually you refer to a text to back up your statement ,but this time you haven't, winging it and relying solely on the fact that the gurus agree with you. Surely you or some guru can come up with a written text that states that propagation is what determine TOA.! That is what this group is all about where gurus debunk the untruths and supply the real truths and not to let old wives tale dominate. You also stated that you made the ":assumption" presumably based on the "facts" stated above that the Curtain could be considered as similar to the dipole since propagation determines that they are the same. This is total junk ,in its entirety, unless you or the gurus can come up with a written text that confirmes their positions. Art "Richard Harrison" wrote in message ... Art Unwin wrote: "---may I go back to the "compared to a dipole" statement which Richard keeps brushing off." I accept a resonant dipole reference as a given. It is true that the antenna under test and the reference dipole have different radiation patterns. Our goal was to compare received signal strengths at locations of interest. The assumption was that on average, the propaqgation was nearly the same for the signals received from both transmitting antennas. Good or bad propagation, the difference between the signals depended on gain in the direction of the receiver as the transmitted power was the same to both antennas no matter where it landed. Kraus says on page 535 of his 3rd edition of "antennas": "Suppose that we express the gain with respect to a single lambda/2 element as the reference antenna. Let the same power P be supplied to this antenna. Then assuming no heat losses, the current Io is the sq rt of the power divided by the resistance of the reference antenna. In general, the gain in field intensity of an array over a reference antenna is given by the ratio of the field intensity from the array to the field intensity from the reference antenna when both are supplied with the same power P." Kraus` example was our intended case. Our expectations were met and our contractors were paid. Best regards, Richard Harrison, KB5WZI |
On Tue, 26 Apr 2005 21:09:07 -0700, Roy Lewallen
wrote: I believe "takeoff angle" is in the same category as "capture area" and "S-unit" -- terms which nobody except amateurs seem to need. Hmmm, Capture area of antennas, 899, 927 of Terman's "Electronic and Radio Engineering. The 899 reference appeals to aperture. The 927 reference gives a value of 1.5 or 0.12 lambda² (also called intercept area or antenna cross section) for a common dipole. Using the co-equivalent aperture, from "Fields and Waves...," Ramo et al., 581, 607-623. The 581 reference is to using reflectors and lenses. The section length treatment relates to literal openings masking a source of radiation. Capture area, 255, 298-301, 495-496 from "TV and Other Receiving Antennas," Bailey - which basically reduces a standard half wave antenna's area to being one half wave long by one quarter wave in width. When we look at the math offered in a later chapter (pg 299) it reduces to 0.12 lambda² a figure already described by Terman. "As we said before, the use of discrete boundaries is a matter of practical convenience." However, Bailey offers a treat in presenting the "capture area" of Arrays of various sizes: # elements Area (lambda²) 1 .125 2 .25 4 0.5 and so on (naively presuming a 3 dB gain with each doubling of elements). As these first three draws off the library shelf have companions on the same shelf with similar coverage, further examples would be redundant. The terms of S-Unit and Take-off angle are more an issue of researching commercial and retail sources than academia. There is some element of elitism in this; but having found that there are volumes of instruction to be found in the commercial world that are barely revealed in the ivory towers, I am not necessarily impressed with sterile pedigrees (the IEEE dictionary is a monument of impotence). 73's Richard Clark, KB7QHC |
On Wed, 27 Apr 2005 03:01:20 +0000 (UTC), "Reg Edwards"
wrote: But if you, as an employee of a reputable laboratory, were given the job of determining the forward and reverse gains of fractal or other weird antennas, at 7 MHz and 144 MHz, what uncertainties would you state? I'd believe you. Hi Reggie, Measurement Mismatch Correction Error 0.04 Noise Power of Power Sensor 0.00 Zero error of Power Sensor 0.00 Power Meter Linearity 0.04 Space Loss Measurement Error 0.01 Multipath Curve Fitting Random Error 0.04 Proximity Effect Correction Error 0.05 The errors remain across all applications, only the assigned values change. If I arbitrarily scaled all values by 25, few could challenge the numbers. At 7MHz we can all agree that the errors are going to be inversely proportional to the astronomical cost to determine. No one is going to perform it at HF when they can only afford 1/100th scale models that offer the accuracies implied above. What would spending more money buy them anyway? 73's Richard Clark, KB7QHC |
On Wed, 27 Apr 2005 03:11:34 GMT, "
wrote: a basis for rejecting. new knoweledge supplied by computor programs Hi Art, More baloney cut thick. You have NOWHERE offered any discussion of ANY new knoweledge (sic); but you hug such manufactured sentiments like an emotional life preserver. You rctleeny challngeed Roy for his athortuy. You wloud do well to leran spllenig bfoere ripeteang that aigan. 73's Richard Clark, KB7QHC |
Reg Edwards wrote:
Richard, why don't you just say that the angle of elevation of the radio path has nothing whatsoever to do with the type of transmitting and receiving antennas, or the directions in which they may be pointing or elevated, or even the operating frequency. Or even the existence of the human race and their radio transmitters. The propagation paths are still there, and even if we had never invented radio they would still exist. Antenna engineering is all about making the best use of the propagation paths that Nature provides[*]. That basic fact should be "bleedin' obvious". [*] The HAARP project does aim to change the ionosphere itself - but the colossal size and power of HAARP only goes to show that "the rest of us" can NOT do that. We cannot change propagation; we can only use it. When communication has been established between A and B, the angle of elevation depends only on the locations of A and B on the Earth's surface, on the number of hops, on the height of the ionospheric layers, and on the slope of the layers. The elevation angle is determined purely by trigonometry. A handy phrase that hasn't been mentioned yet is "ray tracing". That is what we're doing, same as in optics. Received signal strength depends on the two antenna gains in the direction of the path. The take-off angle predicted by Eznec-type programs is an altogether different thing. Hmm... at the risk of proliferating TLAs, how about making a fresh start and calling that the antenna's BVA - Best Vertical Angle? BVA belongs to the antenna, and TOA belongs to the propagation path. It doesn't get around the fact that the antenna radiates something at *all* vertical angles, but it's better than the present situation of (mis)using TOA for two different things. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
On Tue, 26 Apr 2005 20:28:01 -0500, Tom Ring
wrote: Any references on microphone calibration? Maybe a short tutorial? That is something I have a need to do. Hi Tom, Standard microphones (I am being quite specific in terminology here)? I googled with the terms B&K microphone reciprocity and the first hit looks as good as any: http://www.bksv.com/pdf/Bv0051.pdf As a treat, it offers a discussion of matching with transmission line metaphors. I should point out that reciprocity means exactly that! The microphone should be capable as acting as a loudspeaker (certainly not too loud) when driven. Standard microphones are capable of accuracies in the 1/100ths of a dB (and this is an extremely conservative statement). If you are playing with retail microphones, and follow the math, you should be able to cobble up something to the nearest 1/4th dB. If your application conforms to this discussion, you may visit the Brüel & Kjær website to find deeper references. They are the pre-eminent makers of precision sound equipment. As I pointed out in another posting relating to the poverty of academia on many technical subjects, the commercial field often leads the way in actual instruction. 73's Richard Clark, KB7QHC |
On Tue, 26 Apr 2005 20:28:01 -0500, Tom Ring
wrote: Any references on microphone calibration? Maybe a short tutorial? That is something I have a need to do. Hi Tom, As a second thought, you may not be in the market for the reciprocity technique (it does require that you have a true reference microphone). In that case, you would fall back to a Piston Phone and do a single point calibration. The method is as old as the hills, the math is extremely simple volumetrics, but the implementation (construction of the calibration unit) is not something for the faint of heart. You will need a precision lathe. Again, google using Brüel & Kjær as a jump-off point. Once you do the single point calibration, then you can proceed to a swept frequency analysis. Unfortunately this returns us to the necessity of a reference microphone. However, as relative frequency response is more available (from expensive retail models), you might have a chance. 73's Richard Clark, KB7QHC |
|
Well reasoned.
Think of a three-dimensional curve of cost, uncertainty, and frequency to measure gain on a range. Think of a second 3D curve involving modeling. My guess is that below something like 20 MHz (use your own number) modeling is to be preferred. On a related topic: I saw with my own eyes NBS in Boulder (c. 1978) using a different technique to measure gain. It was a near field scheme where a probe was moved in front of the antenna while its vector voltage and position was measured. (As I recall, a pair of lasers was used in the measurement of the probe's x and y position.) The (vast number of) measurements were then imported into a computer that computed the gain. As we say: "you could do that!" I never thought to ask what the expected uncertainties were expected to be. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Richard Clark" wrote in message ... On Wed, 27 Apr 2005 03:01:20 +0000 (UTC), "Reg Edwards" wrote: But if you, as an employee of a reputable laboratory, were given the job of determining the forward and reverse gains of fractal or other weird antennas, at 7 MHz and 144 MHz, what uncertainties would you state? I'd believe you. Hi Reggie, Measurement Mismatch Correction Error 0.04 Noise Power of Power Sensor 0.00 Zero error of Power Sensor 0.00 Power Meter Linearity 0.04 Space Loss Measurement Error 0.01 Multipath Curve Fitting Random Error 0.04 Proximity Effect Correction Error 0.05 The errors remain across all applications, only the assigned values change. If I arbitrarily scaled all values by 25, few could challenge the numbers. At 7MHz we can all agree that the errors are going to be inversely proportional to the astronomical cost to determine. No one is going to perform it at HF when they can only afford 1/100th scale models that offer the accuracies implied above. What would spending more money buy them anyway? 73's Richard Clark, KB7QHC |
On Wed, 27 Apr 2005 09:26:48 -0400, "J. Mc Laughlin"
wrote: Well reasoned. Think of a three-dimensional curve of cost, uncertainty, and frequency to measure gain on a range. Think of a second 3D curve involving modeling. My guess is that below something like 20 MHz (use your own number) modeling is to be preferred. On a related topic: I saw with my own eyes NBS in Boulder (c. 1978) using a different technique to measure gain. It was a near field scheme where a probe was moved in front of the antenna while its vector voltage and position was measured. (As I recall, a pair of lasers was used in the measurement of the probe's x and y position.) The (vast number of) measurements were then imported into a computer that computed the gain. As we say: "you could do that!" I never thought to ask what the expected uncertainties were expected to be. http://www.nearfield.com/ |
Richard Clark wrote:
"Capture area of antennas, 899, 927 of Yerman`s "Electronic and Radio Engineering"." "Capture Area" seems useful to show that the maximum energy you can intercept in a wave is proportional to the product of directive gain and wavelength squared. Terman`s examples show that the microwave antenna`s high gain is offset by the extremely short wavelength. There is only so much energy in a square meter of passing wave. Large antennas access more of it than small ones. I don`t often need to make these calculations. Richard Clark also says Bailey is "naively assuming a 3 dB gain with each doubling of elements." It seems to me that the 2nd, 4th, and 8th element may have the same flaws as the first. No matter how good or bad they are, if they are all similar, wouldn`t (n) elements abstract nX the energy in one element? One of my favorite gems in the newest Kraus "Antennas" is the solved problem on page 705. Solution: (A) The gain of a simple 1/2-wave dipole is 2.15 dBi and of 2 collinear in-phase dipoles is 3.81 dNi. The array of 8 such collinear dipoles adds 3 +3 = 9 dB. The reflector screen adds 3 dB more and the ground bounce another 6 dB for a total gain of 3.8 + 9 +3 +6 = 21.8 dBi." This is the gain of the Deutche Welle antenna which appears on the rear cover of my copy. Best regards, Richard Harrison, KB5WZI |
Richard Clark wrote:
On Wed, 27 Apr 2005 03:11:34 GMT, " wrote: a basis for rejecting. new knoweledge supplied by computor programs Hi Art, More baloney cut thick. You have NOWHERE offered any discussion of ANY new knoweledge (sic); but you hug such manufactured sentiments like an emotional life preserver. You rctleeny challngeed Roy for his athortuy. You wloud do well to leran spllenig bfoere ripeteang that aigan. What I want to know is how we are going to alter reality when the computer program shows it is wrong! - Mike KB3EIA - |
Richard Harrison wrote:
. . . Richard Clark also says Bailey is "naively assuming a 3 dB gain with each doubling of elements." It seems to me that the 2nd, 4th, and 8th element may have the same flaws as the first. No matter how good or bad they are, if they are all similar, wouldn`t (n) elements abstract nX the energy in one element? . . . Yes, but the amount extracted by one element is affected by the presence of the others. So adding or removing an element changes the amount extracted by all the other elements. The effect is known as "mutual coupling", and it explains why, for example, a 2 element Yagi or other two element array can have gain greater than (or less than) 3 dB relative to a single element. Roy Lewallen, W7EL |
Roy Lewallen, W7EL wrote:
"Yes, but the amount extracted by one element is affected by the presence of the others. So adding or moving an element changes the amount extracted by all the other elements." Thank you. Mutual impedance can add or subtract from a total. I assumed the designer would be deliberately combining elements in such a way as to maximize total gain. Plans don`t always work the way we hope. Best regards, Richard Harrison, KB5WZI |
Richard Fry posted a beautiful picture of a Harris / Gates test facility
in which an antenna tower is rotated and tilted up to 90-degrees, I suppose. Nice way to get the antenna pattern. Hope Harris had a government contract number to charge that job to. Best regards, Richard Harrison, KB5WZI |
From: "Richard Harrison"
Richard Fry posted a beautiful picture of a Harris / Gates test facility in which an antenna tower is rotated and tilted up to 90-degrees, I suppose. Nice way to get the antenna pattern. Hope Harris had a government contract number to charge that job to. ________________ Azimuth patterns were taken by spinning the antenna+tower around a horizontal axis centered above the two trestle supports you see in the scanned photo. The AUT is positioned broadside to the source antenna. Elevation patterns were taken by spinning the whole assembly in the horizontal plane, on the horizontal centerline of the antenna+tower assembly. The trestles sit on a huge wooden beam which itself is supported by, and centered on a motor-driven turntable -- making that possible. So both sets of patterns can be taken without needing to put the antenna+tower in the vertical plane (no tilting to 90 degrees is necessary). However we had several other positioners for vertical antennas to use when the measurement of elevation patterns was not required. Yes, this customer had deep pockets, but was not a government agency. Just a major broadcast group. RF |
Correction. Even identical array elements *don't* necessarily extract
the same amount of energy. The reason again is mutual coupling. In a four-square receiving array with very low ground loss, one of the elements will actually radiate power. This power comes from power extracted from the wave by the other three. In a Yagi array, the parasitic elements extract no power at all from an impinging wave; only the driven element does. Roy Lewallen, W7EL Roy Lewallen wrote: Richard Harrison wrote: . . . Richard Clark also says Bailey is "naively assuming a 3 dB gain with each doubling of elements." It seems to me that the 2nd, 4th, and 8th element may have the same flaws as the first. No matter how good or bad they are, if they are all similar, wouldn`t (n) elements abstract nX the energy in one element? . . . Yes, but the amount extracted by one element is affected by the presence of the others. So adding or removing an element changes the amount extracted by all the other elements. The effect is known as "mutual coupling", and it explains why, for example, a 2 element Yagi or other two element array can have gain greater than (or less than) 3 dB relative to a single element. Roy Lewallen, W7EL |
Roy Lewallen, W7EL wrote:
"Even identical array elements "don`t" necessarily extract the same amount of energy. The reason is again mutual coupling." Yes, and driven elements have a load. Parasitics do not. In a parasitic array, the field strength at a distant point is a function of the currents in both elements when it consists of two dipoles. It is true "the parasitic element extracts no power from an impinging wave". It has no load to accept the power. It is a short-corcuit rod or wire. It has current induced from a passing wave of acceptable direction and frequency whether its source is from a driven element or from a far away transmitter. The excitation of a parasitic element, if no heat is produced in the slemsnt. is 100% re-radiated. The element has a resistance which consists of its self resistance and its mutual resistances. The total composes the radiation resistance of the element which is the source resistance for the radiation from the element. My original comment was in support of Arnold B. Bailey who said something about increasing antenna gain by 3 dB every time you double its size. Precisely, that`s not true, but I gave an example from Kraus where he did much the same thing. Best regards, Richard Harrison, KB5WZI |
Richard Clark wrote:
On Tue, 26 Apr 2005 20:28:01 -0500, Tom Ring wrote: Any references on microphone calibration? Maybe a short tutorial? That is something I have a need to do. Hi Tom, Standard microphones (I am being quite specific in terminology here)? I googled with the terms B&K microphone reciprocity snip 73's Richard Clark, KB7QHC Thanks. tom K0TAR |
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