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"Miracle" DLM RI short vertical
Howdy NGers,
I was curious about another "miracle" short vertical, being subject of great interest, patent by Robert Vincent and Physics dept. of University of Rhode Island. I got up at 4 am, drove to Boxboro ARRL convention and eager to see what are we missing. Not much! Giveaway was opening statement something like: how to make shortened antenna with more gain (compare to what? I guess light bulb :-) In the "theoretical" portion of the presentation audience was told that current across the helical coil decreases away from the feed point, while across loading coil it stays constant. Due overcrowding of "inventor" I did not persist in breaking through and asking for enlightenment. Author claims more gain (familiar), better bandwidth (doesn't get it why) and small size (of course). Showing measured graphs with current and phase distribution along the radiator. Works very well! (Many stations worked.) He showed how to measure current at the antenna using ferrite pickup transformer way up the antenna and cables to the instrument (handsomely detuning and distorting the measurements). I suspect that "broad bandwidth", (SWR 2:1) was achieved thanks to losses in the coils and dielectric, as "confirmed" by his statement that coils were fried when power was applied. What is it? Basically helically wound coil starting from the base, about half way up the radiator, then piece of straight tubing, than loading coil, then tubing and in some case top hat (works better :-). Matching to 50 ohms is done by picking tap at the base, few coil turns up. That is 3D version. He showed some "2D" versions, having "coils" made of basically coil formed as hairpin loops instead of classic solenoid, also the loading coil. So kind of 2D - 3D antenna :-) I wanted to make a bet that my single loading coil loaded vertical would cream the "miracle", but there were so many worshippers paying compliments to the inventor, that I resigned not to stay for the second hour of lecture how to build it. I saw no trace of any modeling, just experiments using wrong tools. So brace yourselves for another "miracle" in the arsenal of very small and more efficient antennas. It should be a hit with CBers and other suckered users. So that's it (oh, no chokes in the feedlines), I hope U of RI is proud of this breakthrough, I can sleep well now. Back to DR1. Yuri, K3BU with more info that could have saved lotsa experimenting at http://www.k3bu.us/loadingcoils.htm |
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Does it also plug into the house wiring for improved TV reception? Gotta love junk-science! Howard Not sure, but it is apparently very easy to scale up or down by simply reducing/enlarging it on the copier by factor x. No kidding! Apparently works well into the UHF bands :-) Who needs EZnec. Can you picture all them wizards joining forces for FracEHDLMCFA gizmo? Yuri |
Yuri Blanarovich wrote:
In the "theoretical" portion of the presentation audience was told that current across the helical coil decreases away from the feed point, while across loading coil it stays constant. I've often wondered at exactly what crossover point a helical coil turns into a loading coil. If one adds a one inch stinger to a helical coil, does that turn it into a loading coil? How about a one foot stinger? Is a one foot long loading coil not a helical coil? Does a one foot long loading coil really have less phase shift than a one foot long piece of wire? On a center-loaded mobile antenna, how can the ARCCOS of the current at the feedpoint be zero degrees and the ARCCOS of the current at the tip be 90 degrees without there being 90 degrees between the feedpoint and the tip? (When are you going to invite everyone over to Bar-B-Q that sacred cow?) -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Yuri, your criticism is perfectly sound.
To sum up, the key to antenna radiating efficiency is SIMPLICITY. The more simple the construction of an antenna the more efficient it will be. It is intuitivly obvious. Every complication is sure to introduce loss. --- Reg |
Reg Edwards wrote:
The more simple the construction of an antenna the more efficient it will be. An isotropic is pretty simple but I don't know how to feed it. :-) -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
I wish someone WOULD come up with a 10-ft vertical for 80 meters with the
same gain and bandwidth as a simple dipole "Yuri Blanarovich" wrote in message ... Howdy NGers, I was curious about another "miracle" short vertical, being subject of great interest, patent by Robert Vincent and Physics dept. of University of Rhode Island. I got up at 4 am, drove to Boxboro ARRL convention and eager to see what are we missing. Not much! Giveaway was opening statement something like: how to make shortened antenna with more gain (compare to what? I guess light bulb :-) In the "theoretical" portion of the presentation audience was told that current across the helical coil decreases away from the feed point, while across loading coil it stays constant. Due overcrowding of "inventor" I did not persist in breaking through and asking for enlightenment. Author claims more gain (familiar), better bandwidth (doesn't get it why) and small size (of course). Showing measured graphs with current and phase distribution along the radiator. Works very well! (Many stations worked.) He showed how to measure current at the antenna using ferrite pickup transformer way up the antenna and cables to the instrument (handsomely detuning and distorting the measurements). I suspect that "broad bandwidth", (SWR 2:1) was achieved thanks to losses in the coils and dielectric, as "confirmed" by his statement that coils were fried when power was applied. What is it? Basically helically wound coil starting from the base, about half way up the radiator, then piece of straight tubing, than loading coil, then tubing and in some case top hat (works better :-). Matching to 50 ohms is done by picking tap at the base, few coil turns up. That is 3D version. He showed some "2D" versions, having "coils" made of basically coil formed as hairpin loops instead of classic solenoid, also the loading coil. So kind of 2D - 3D antenna :-) I wanted to make a bet that my single loading coil loaded vertical would cream the "miracle", but there were so many worshippers paying compliments to the inventor, that I resigned not to stay for the second hour of lecture how to build it. I saw no trace of any modeling, just experiments using wrong tools. So brace yourselves for another "miracle" in the arsenal of very small and more efficient antennas. It should be a hit with CBers and other suckered users. So that's it (oh, no chokes in the feedlines), I hope U of RI is proud of this breakthrough, I can sleep well now. Back to DR1. Yuri, K3BU with more info that could have saved lotsa experimenting at http://www.k3bu.us/loadingcoils.htm --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.732 / Virus Database: 486 - Release Date: 7/30/2004 |
"Cecil Moore" wrote in message ... Reg Edwards wrote: The more simple the construction of an antenna the more efficient it will be. An isotropic is pretty simple but I don't know how to feed it. :-) From the inside. Ed wb6wsn |
There were about 80 people at the talk, including a number of hams who are/were
antenna professionals; academics; and so on. I was there for most of it; it was two hours and thus had the time frame for a substantial brief. I saw and heard nothing that--in my opinion-- constitutes 'new' or 'revolutionary'. Although the statement "97% efficiency " was made for a shortened, DLM by Mr. Vincent, I saw no data that supported that claim. I did not see wide bandwidths in the data. The antennas are small. That claim is supported. I did not see any evidence of improvement over the extant art of distributed loading. What I saw essentially confirms my earlier comments from June and July in this forum. Note: I was not aware of Mr. Vincent's design for the DLM until yesterday. If I missed something, or make a statement here that is factually inaccurate regarding the statements of Mr. Vincent, apologies ahead of time; and please fill me in on this forum. As promised earlier relative to the extant prior art: I draw reference to an existing, patent pending, commercial antenna by our friends at Astatic (the microphone company). It is sold by Omnitronics. It is called the "3K Antenna". The antenna is targeted for CB'ers and truckers, but it also works and is used, by hams on 10M. It , in appearance, looks identical to some of the DLM antennas Mr. Vincent presented. There is an inside cutaway which shows, in part , a vertically oriented helix (linear load); a "midsection"; a loading coil; and a top whip. I have one here. See: http://www.astatic.com Mr. Vincent confirmed that he was unaware of the Astatic antenna until I mentioned it to him yesterday. I have offered to elaborate on a critique of Mr. Vincent's technology on the web, which I will produce, if needed. It may not be necessary for me to educate this way, as a number of people were/are capable of such assessments based on the info provided, and Mr. Vincent stated that he will post the PPT of the talk on the web. Doubtless there will be further independent discussion. Just as a matter of protocol, in a public talk that has benefited from many years of guidance under an academic physics department, may I make the following brief (albeit not complete) suggestions: 1) Understand that a widely spaced helix has air cooling such that the cooling rate can substantially exceed the heating rate. Therefore the helix may dissipate heat and does not heat up much. That does not mean the system is lossless, nor that the efficiency through the helix is high. 2) Never claim that the efficiency of any electronic component as 100% ("lossless through the helix") just because the current profile stays relatively flat across it, and it doesn't burn up. 3) We have all used chicken wire(as ground screens), but may it strongly be discouraged. The losses are frequency dependent and often high; 4) Do not discount any ground counterpoise--especially one with 1/8 wave radials as being --in considering monopoles. It is an antenna system. This is part of the system; 5) Avoid PVC in monopole construction. At some frequencies the losses are reasonable, at others it is high. It varies from manufacturer; thickness; and so on. 6) Do not compare gains on a thin-wire type 1/4 wave monopole to a thick (diameter) helix-based antenna with a far larger electrical length, over a lossy, small counterpoise, and infer the efficiency. 7) Do not use wood in the near field when using MF/HF for probe measurements. My brief thoughts at moment. More later if needed. 73, Chip N1IR |
Hal Rosser wrote:
I wish someone WOULD come up with a 10-ft vertical for 80 meters with the same gain and bandwidth as a simple dipole Heck Hal, a 66 ft. vertical for 80m doesn't even have the same gain as a dipole. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Did they mention where an actual drawing can be found
or if an indepth descriptive article can be found? Thanks Art "Fractenna" wrote in message ... There were about 80 people at the talk, including a number of hams who are/were antenna professionals; academics; and so on. I was there for most of it; it was two hours and thus had the time frame for a substantial brief. I saw and heard nothing that--in my opinion-- constitutes 'new' or 'revolutionary'. Although the statement "97% efficiency " was made for a shortened, DLM by Mr. Vincent, I saw no data that supported that claim. I did not see wide bandwidths in the data. The antennas are small. That claim is supported. I did not see any evidence of improvement over the extant art of distributed loading. What I saw essentially confirms my earlier comments from June and July in this forum. Note: I was not aware of Mr. Vincent's design for the DLM until yesterday. If I missed something, or make a statement here that is factually inaccurate regarding the statements of Mr. Vincent, apologies ahead of time; and please fill me in on this forum. As promised earlier relative to the extant prior art: I draw reference to an existing, patent pending, commercial antenna by our friends at Astatic (the microphone company). It is sold by Omnitronics. It is called the "3K Antenna". The antenna is targeted for CB'ers and truckers, but it also works and is used, by hams on 10M. It , in appearance, looks identical to some of the DLM antennas Mr. Vincent presented. There is an inside cutaway which shows, in part , a vertically oriented helix (linear load); a "midsection"; a loading coil; and a top whip. I have one here. See: http://www.astatic.com Mr. Vincent confirmed that he was unaware of the Astatic antenna until I mentioned it to him yesterday. I have offered to elaborate on a critique of Mr. Vincent's technology on the web, which I will produce, if needed. It may not be necessary for me to educate this way, as a number of people were/are capable of such assessments based on the info provided, and Mr. Vincent stated that he will post the PPT of the talk on the web. Doubtless there will be further independent discussion. Just as a matter of protocol, in a public talk that has benefited from many years of guidance under an academic physics department, may I make the following brief (albeit not complete) suggestions: 1) Understand that a widely spaced helix has air cooling such that the cooling rate can substantially exceed the heating rate. Therefore the helix may dissipate heat and does not heat up much. That does not mean the system is lossless, nor that the efficiency through the helix is high. 2) Never claim that the efficiency of any electronic component as 100% ("lossless through the helix") just because the current profile stays relatively flat across it, and it doesn't burn up. 3) We have all used chicken wire(as ground screens), but may it strongly be discouraged. The losses are frequency dependent and often high; 4) Do not discount any ground counterpoise--especially one with 1/8 wave radials as being --in considering monopoles. It is an antenna system. This is part of the system; 5) Avoid PVC in monopole construction. At some frequencies the losses are reasonable, at others it is high. It varies from manufacturer; thickness; and so on. 6) Do not compare gains on a thin-wire type 1/4 wave monopole to a thick (diameter) helix-based antenna with a far larger electrical length, over a lossy, small counterpoise, and infer the efficiency. 7) Do not use wood in the near field when using MF/HF for probe measurements. My brief thoughts at moment. More later if needed. 73, Chip N1IR |
I've often wondered at exactly what crossover point a helical coil turns into a loading coil. If one adds a one inch stinger to a helical coil, does that turn it into a loading coil? How about a one foot stinger? Is a one foot long loading coil not a helical coil? Does a one foot long loading coil really have less phase shift than a one foot long piece of wire? On a center-loaded mobile antenna, how can the ARCCOS of the current at the feedpoint be zero degrees and the ARCCOS of the current at the tip be 90 degrees without there being 90 degrees between the feedpoint and the tip? (When are you going to invite everyone over to Bar-B-Q that sacred cow?) -- 73, Cecil http://www.qsl.net/w5dxp We have to wait for the patent 'splaining the "miracle". One thing I "discovered" that winding the wire either as a coil or simply taping it to the wood or plastic dielectric detunes the heck of it (losses, making it look more "broadband"). I taped the wire of quarter wave vertical to the bamboo pole, and it was way off resonance. When I put plexiglass spacers, insulators, bingo, right on frequency. Coil is a coil and in the antenna circuit it behaves that way. One thing is comapring quarter wave electrical length (loaded) radiator to quarter wave monopole, another thing is making it electrically longer, loading it and then comparing to quarter wave radiator. From presentation it was hard to judge what exactly was DLM electrically equivalet to. We might have clinic on verticals over "perfect" salty water soon, we are closing on waterfront property near the Ocean Gate old AT&T huge Rhombic antenna farm and looking for some juicy coiled sausage to BBQ. I think that hanging cow bell and flourescent light on the DLM would make it one class better, maybe 120% efficient antenna :-) What will they think of next? 73 Yuri, K3BU.us |
Did they mention where an actual drawing can be found
or if an indepth descriptive article can be found? Thanks Art What I described, says it all. The variation from the helically wound coil at the bottom half of the radiator is the trombone like "coil" or loading stubs. Looks like one or two turn trombone loading stubs along the radiator. This should model in EZnec and show how the current decreases. Not much different from the loading coil at the base, which any mobile aficionado knows is the worst place to put the loading coil at. Again. It is vertical, working against radials, or screen, loaded at the base with helical coil or trombone, then piece of tubing, then loading coil, than piece of tubing (stinger) or top hat. You can play with any sizes you like, it will not beat "classic" whip with loading coil about 2/3 up the radiator. When the patent is issued and published, you will be able to see where the "secret" is. He promised to have something on the web site, but I did not bother to take a note of it. 73 Yuri, K3BU.us www.computeradio.us home of Dream Radio One |
Yuri
What I find hard to understand is that the University has placed its name behind it.! The professors at the university had years to review the design and I presume stood behing it. I also understand that actual measurements were taken albiet possibly with misuse of equipment.. I also find it odd that the ARRL did not get a jump on it before today as the inventor has connections with them. and wide spread notice that he also was a ham. FCC is probably snickering now about ham operator statments including those of the ARRL comments regarding use of power lines Its a shame that the ARRL will take a laid back aproach on this antenna until they have had a chance to review comments from elswhere. There must be something that was missed at the show possibly because of a prior belief that it was a fake regardless of what he said. In the mean time I accept your analysis sinc eyou were there as was Chip. Hopefully Tom W8TI was there and jotted down drawings from the' how to make' session so that he can point out errors and falacies in the analysis from the first session where many graphs were presented of the findings and possibly the technology behind it Regards Art "Yuri Blanarovich" wrote in message ... Did they mention where an actual drawing can be found or if an indepth descriptive article can be found? Thanks Art What I described, says it all. The variation from the helically wound coil at the bottom half of the radiator is the trombone like "coil" or loading stubs. Looks like one or two turn trombone loading stubs along the radiator. This should model in EZnec and show how the current decreases. Not much different from the loading coil at the base, which any mobile aficionado knows is the worst place to put the loading coil at. Again. It is vertical, working against radials, or screen, loaded at the base with helical coil or trombone, then piece of tubing, then loading coil, than piece of tubing (stinger) or top hat. You can play with any sizes you like, it will not beat "classic" whip with loading coil about 2/3 up the radiator. When the patent is issued and published, you will be able to see where the "secret" is. He promised to have something on the web site, but I did not bother to take a note of it. 73 Yuri, K3BU.us www.computeradio.us home of Dream Radio One |
Institution or magazine is only as good as people in it. Obviously UofRI does not have RF department, otherwise the technician would not be the star "inventor", if they had even dummy like me, that would not fly out into the press release and patent office. (Well, you can patent anything now a days, but why waste money, unless you expect to fool some clueless buyers.) ARRL and QST is slipping in quality and reviewing what goes out. See the wrong "wisdom" of distribution of current in the loading coils that was started by Belrose in the 50ies and propagated through Compendia and ARRL Antenna book and defended by W8JI till this modern times. There are more half baked articles showing up with time. Internet helps to discuss and correct some stuff, but seems that with time, we are getting more "experts" discovering perpetuum mobile and getting away with it. Good thing it is only a hobby and some bright minds are still around at this NG :-) 73 Yuri Yuri What I find hard to understand is that the University has placed its name behind it.! The professors at the university had years to review the design and I presume stood behing it. I also understand that actual measurements were taken albiet possibly with misuse of equipment.. I also find it odd that the ARRL did not get a jump on it before today as the inventor has connections with them. and wide spread notice that he also was a ham. FCC is probably snickering now about ham operator statments including those of the ARRL comments regarding use of power lines Its a shame that the ARRL will take a laid back aproach on this antenna until they have had a chance to review comments from elswhere. There must be something that was missed at the show possibly because of a prior belief that it was a fake regardless of what he said. In the mean time I accept your analysis sinc eyou were there as was Chip. Hopefully Tom W8TI was there and jotted down drawings from the' how to make' session so that he can point out errors and falacies in the analysis from the first session where many graphs were presented of the findings and possibly the technology behind it Regards Art |
You make some good points
Regards Art "Yuri Blanarovich" wrote in message ... Institution or magazine is only as good as people in it. Obviously UofRI does not have RF department, otherwise the technician would not be the star "inventor", if they had even dummy like me, that would not fly out into the press release and patent office. (Well, you can patent anything now a days, but why waste money, unless you expect to fool some clueless buyers.) ARRL and QST is slipping in quality and reviewing what goes out. See the wrong "wisdom" of distribution of current in the loading coils that was started by Belrose in the 50ies and propagated through Compendia and ARRL Antenna book and defended by W8JI till this modern times. There are more half baked articles showing up with time. Internet helps to discuss and correct some stuff, but seems that with time, we are getting more "experts" discovering perpetuum mobile and getting away with it. Good thing it is only a hobby and some bright minds are still around at this NG :-) 73 Yuri Yuri What I find hard to understand is that the University has placed its name behind it.! The professors at the university had years to review the design and I presume stood behing it. I also understand that actual measurements were taken albiet possibly with misuse of equipment.. I also find it odd that the ARRL did not get a jump on it before today as the inventor has connections with them. and wide spread notice that he also was a ham. FCC is probably snickering now about ham operator statments including those of the ARRL comments regarding use of power lines Its a shame that the ARRL will take a laid back aproach on this antenna until they have had a chance to review comments from elswhere. There must be something that was missed at the show possibly because of a prior belief that it was a fake regardless of what he said. In the mean time I accept your analysis sinc eyou were there as was Chip. Hopefully Tom W8TI was there and jotted down drawings from the' how to make' session so that he can point out errors and falacies in the analysis from the first session where many graphs were presented of the findings and possibly the technology behind it Regards Art |
Yuri
Does this antenna have an upper limit on the frequency it'll operate at? I'd think some real life data on efficiency could be derived from enclosing anantenna in a 'big enough' styrofoam cooler type enclosure. If the parts that *I* suspect to be lossy might cause a significant temperature rise with several hundred watts fed to the antenna. Jerry "Yuri Blanarovich" wrote in message ... Institution or magazine is only as good as people in it. Obviously UofRI does not have RF department, otherwise the technician would not be the star "inventor", if they had even dummy like me, that would not fly out into the press release and patent office. (Well, you can patent anything now a days, but why waste money, unless you expect to fool some clueless buyers.) ARRL and QST is slipping in quality and reviewing what goes out. See the wrong "wisdom" of distribution of current in the loading coils that was started by Belrose in the 50ies and propagated through Compendia and ARRL Antenna book and defended by W8JI till this modern times. There are more half baked articles showing up with time. Internet helps to discuss and correct some stuff, but seems that with time, we are getting more "experts" discovering perpetuum mobile and getting away with it. Good thing it is only a hobby and some bright minds are still around at this NG :-) 73 Yuri Yuri What I find hard to understand is that the University has placed its name behind it.! The professors at the university had years to review the design and I presume stood behing it. I also understand that actual measurements were taken albiet possibly with misuse of equipment.. I also find it odd that the ARRL did not get a jump on it before today as the inventor has connections with them. and wide spread notice that he also was a ham. FCC is probably snickering now about ham operator statments including those of the ARRL comments regarding use of power lines Its a shame that the ARRL will take a laid back aproach on this antenna until they have had a chance to review comments from elswhere. There must be something that was missed at the show possibly because of a prior belief that it was a fake regardless of what he said. In the mean time I accept your analysis sinc eyou were there as was Chip. Hopefully Tom W8TI was there and jotted down drawings from the' how to make' session so that he can point out errors and falacies in the analysis from the first session where many graphs were presented of the findings and possibly the technology behind it Regards Art |
Does this antenna have an upper limit on the frequency it'll operate at? I'd think some real life data on efficiency could be derived from enclosing anantenna in a 'big enough' styrofoam cooler type enclosure. If the parts that *I* suspect to be lossy might cause a significant temperature rise with several hundred watts fed to the antenna. Jerry There is no limit on the operating frequency of any antenna. If you can feed RF into it, it will radiate. Question is where, pattern is determined by the electrical length of the radiator. The real efficiency of shortened antenna should be indicated by the comparison with full size equivalent (or any other known type) and measured field strength, like it is done in mobile antenna shootouts. Any RF energy lost in heat is not radiated and will show up in lower signal levels. It is important to compare antennas with the same radiation pattern and ground system. Yuri, K3BU.us |
Does this antenna have an upper limit on the frequency it'll operate at?
I'd think some real life data on efficiency could be derived from enclosing anantenna in a 'big enough' styrofoam cooler type enclosure. If the parts that *I* suspect to be lossy might cause a significant temperature rise with several hundred watts fed to the antenna. Jerry No report , that I am aware, of Wheeler cap measurements. Antenna is monochromatic and moderate/hi Q. 73, Chip N1IR |
"Yuri Blanarovich" wrote in message ... Does this antenna have an upper limit on the frequency it'll operate at? I'd think some real life data on efficiency could be derived from enclosing anantenna in a 'big enough' styrofoam cooler type enclosure. If the parts that *I* suspect to be lossy might cause a significant temperature rise with several hundred watts fed to the antenna. Jerry There is no limit on the operating frequency of any antenna. If you can feed RF into it, it will radiate. Question is where, pattern is determined by the electrical length of the radiator. The real efficiency of shortened antenna should be indicated by the comparison with full size equivalent (or any other known type) and measured field strength, like it is done in mobile antenna shootouts. Any RF energy lost in heat is not radiated and will show up in lower signal levels. It is important to compare antennas with the same radiation pattern and ground system. Yuri, K3BU.us Yuri Youve gotten too refined. I mostly know about basic antenna theory and modeling. But building a VHF model of a 40 meter antenna with #12 copper wire wound around a 4 inch mandril might be impractical. But, if the "wonder antenna" is small enough to be enclosed (mostly) in something transparent to the RF but not to the thermal thats generated by any I^2* R losses, wouldnt the temperture rise inside the enclosure give a decent indication of efficiency? If this "wonder antenna" designer claims to be able to shape the radiation pattern with an antenna significantly shorter that a 1/4 wave stub, He really has something. I suspect that the something he has is mental illness. I've been following this info on the RI antenna and have considered it to be so 'snake oilish' that it would never see the light of an auditorium. Your post about attending the lecture made me wonder if anyone asked about *any* simple (approximations) measurements like the styrofoam radome to get some idea of the I^2*R power lost in the antenna. If he has an antenna, and a transmitter and enough room to build a foam igloo it seems that alot of data on efficiency could be obtained. If I had any interest in describing an antenna I'd built, I'd at least use an infared thermometer on the section of the antenna suspected as being the most lossy. Jerry |
There's a fundamental problem in making a scale model of an antenna to
determine loss -- the wire conductivity has to be scaled with frequency. Of course, the wire diameter can be changed from the normally scaled size in order to create the same loss, but then the antenna might behave differently. It's not clear to me how you could get quantitative data from measurements in a styrofoam container. Let's say you put 100 watts into the antenna for five minutes and the temperature rise (of the coil? helical winding? air?) was 10 degrees C. How would you calculate the loss or efficiency from that information? Roy Lewallen, W7EL Jerry Martes wrote: Youve gotten too refined. I mostly know about basic antenna theory and modeling. But building a VHF model of a 40 meter antenna with #12 copper wire wound around a 4 inch mandril might be impractical. But, if the "wonder antenna" is small enough to be enclosed (mostly) in something transparent to the RF but not to the thermal thats generated by any I^2* R losses, wouldnt the temperture rise inside the enclosure give a decent indication of efficiency? If this "wonder antenna" designer claims to be able to shape the radiation pattern with an antenna significantly shorter that a 1/4 wave stub, He really has something. I suspect that the something he has is mental illness. I've been following this info on the RI antenna and have considered it to be so 'snake oilish' that it would never see the light of an auditorium. Your post about attending the lecture made me wonder if anyone asked about *any* simple (approximations) measurements like the styrofoam radome to get some idea of the I^2*R power lost in the antenna. If he has an antenna, and a transmitter and enough room to build a foam igloo it seems that alot of data on efficiency could be obtained. If I had any interest in describing an antenna I'd built, I'd at least use an infared thermometer on the section of the antenna suspected as being the most lossy. Jerry |
Roy
I'm a real slopy builder. So, I do alot of half-assed things. I might begin with a 100 watt light bulb inside the "icebox" to establish a referance temperature. maybe even a 50 watt and even a 25 watt. And, if the antenna could be modeled at some frequency where I could build an ice box thats sufficiently transparent to RF, like 6 Meters, I'd build a full size antenna for use as a referance. I've never done something like this. It just sems very practical, since a 100% efficient antenna wouldnt introduce any heat. But , a 50% efficient one might produce about the same heat as a 50 watt light bulb. I'd not declare this "ice box" to be a Lab Standard. But, if there was need, I'd sure try to evaluate the concept. When people like you cast doubt on anything I tink up, I begin to doubt myself. Jerry "Roy Lewallen" wrote in message ... There's a fundamental problem in making a scale model of an antenna to determine loss -- the wire conductivity has to be scaled with frequency. Of course, the wire diameter can be changed from the normally scaled size in order to create the same loss, but then the antenna might behave differently. It's not clear to me how you could get quantitative data from measurements in a styrofoam container. Let's say you put 100 watts into the antenna for five minutes and the temperature rise (of the coil? helical winding? air?) was 10 degrees C. How would you calculate the loss or efficiency from that information? Roy Lewallen, W7EL Jerry Martes wrote: Youve gotten too refined. I mostly know about basic antenna theory and modeling. But building a VHF model of a 40 meter antenna with #12 copper wire wound around a 4 inch mandril might be impractical. But, if the "wonder antenna" is small enough to be enclosed (mostly) in something transparent to the RF but not to the thermal thats generated by any I^2* R losses, wouldnt the temperture rise inside the enclosure give a decent indication of efficiency? If this "wonder antenna" designer claims to be able to shape the radiation pattern with an antenna significantly shorter that a 1/4 wave stub, He really has something. I suspect that the something he has is mental illness. I've been following this info on the RI antenna and have considered it to be so 'snake oilish' that it would never see the light of an auditorium. Your post about attending the lecture made me wonder if anyone asked about *any* simple (approximations) measurements like the styrofoam radome to get some idea of the I^2*R power lost in the antenna. If he has an antenna, and a transmitter and enough room to build a foam igloo it seems that alot of data on efficiency could be obtained. If I had any interest in describing an antenna I'd built, I'd at least use an infared thermometer on the section of the antenna suspected as being the most lossy. Jerry |
But, if the "wonder antenna" is small enough to be enclosed (mostly) in
something transparent to the RF but not to the thermal thats generated by any I^2* R losses, wouldnt the temperture rise inside the enclosure give a decent indication of efficiency? No need for that really, too cumbersome. If you measure R you can calculate losses due to dissipation in heat. Again, real comparison of efficiency of shortened antenna is to compare against the same pattern producing full (electrical) length antenna, everything is included in what you would measure. Much simpler too. I can build quarter wave vertical faster than styrofoam igloo. :-) Basic rules are, best inductive loading is about 2/3 up the radiator, coil is better than loading stub, top hat is the best. Anything else is jocker's attempt at perpetuum mobile. Yuri |
Jerry Martes wrote:
Roy I'm a real slopy builder. So, I do alot of half-assed things. I might begin with a 100 watt light bulb inside the "icebox" to establish a referance temperature. maybe even a 50 watt and even a 25 watt. And, if the antenna could be modeled at some frequency where I could build an ice box thats sufficiently transparent to RF, like 6 Meters, I'd build a full size antenna for use as a referance. I've never done something like this. It just sems very practical, since a 100% efficient antenna wouldnt introduce any heat. But , a 50% efficient one might produce about the same heat as a 50 watt light bulb. It would if the thermal mass of the antenna were the same as the light bulb, and if the thermal loss through the wiring were the same for the antenna as for the light bulb. But otherwise, they could be vastly different. I'd not declare this "ice box" to be a Lab Standard. But, if there was need, I'd sure try to evaluate the concept. When people like you cast doubt on anything I tink up, I begin to doubt myself. Jerry Well, then I've done a good service. Only when you have doubts about your methodolgy will you have any incentive to take the time to try and understand what you're doing. Any conclusions you reach about the antenna's efficiency (except that it's not 100% efficient - duh) will be completely worthless unless you get at least some kind of handle on the relationship between the heat and the temperature. Roy Lewallen, W7EL |
Yuri I sure disagree about being able to determine an antenna's efficiency by either resistance measurements or by measuring received signa;l strength at any one point in space. But, you are certainly a much smarter fuy than I ever was. So, I am not equipped to get into a news group contest. It is my contention that the antenna under test's complete radiation pattern and field strength would have to be measured and integrated if field strength is used to determine it's efficiency. That could get coplicated. It would have seemed to me that the loss in any "R" is dependent on the current flowing in it. And, I'd be concerned that any resonances could have higher circulating currents at the operating frequency. If you can point out the errors in my convictions, I'd like to read about where I'm wrong. Jerry "Yuri Blanarovich" wrote in message ... But, if the "wonder antenna" is small enough to be enclosed (mostly) in something transparent to the RF but not to the thermal thats generated by any I^2* R losses, wouldnt the temperture rise inside the enclosure give a decent indication of efficiency? No need for that really, too cumbersome. If you measure R you can calculate losses due to dissipation in heat. Again, real comparison of efficiency of shortened antenna is to compare against the same pattern producing full (electrical) length antenna, everything is included in what you would measure. Much simpler too. I can build quarter wave vertical faster than styrofoam igloo. :-) Basic rules are, best inductive loading is about 2/3 up the radiator, coil is better than loading stub, top hat is the best. Anything else is jocker's attempt at perpetuum mobile. Yuri |
The most intelligent, sensible and successful radio engineers make no attempt to measure antenna radiating efficiency. It never occurs to them to do so - they invariably calculate it. It takes no longer than a couple of minutes on the back of a used envelope, using a pocket calculator. It is more accurate and is absolutely certain to be enormously less expensive. But perhaps some old wife who cannot do simple arithmetic will find a fellow creature somewhere in Google who is reported as having attempted to measure it. The real problem lies in the western world's educational system. Arithmetic has been neglected for far too long. It will take two generations to return to normal and dis-arm children who take loaded guns, even automatic weapons, to school. Never mind about tower blocks. As a priority, teachers must be protected from acts of terrorism. But too late. Chinese and other Eastern countries' education, science, engineering and technology will have already acheived supremacy. But why make a battle out of it? I'm sure the peaceful, generous, Chinese will be quite willing to share the products of their educational system. ---- Reg, G4FGQ |
"Roy Lewallen" wrote in message ... Jerry Martes wrote: Roy I'm a real slopy builder. So, I do alot of half-assed things. I might begin with a 100 watt light bulb inside the "icebox" to establish a referance temperature. maybe even a 50 watt and even a 25 watt. And, if the antenna could be modeled at some frequency where I could build an ice box thats sufficiently transparent to RF, like 6 Meters, I'd build a full size antenna for use as a referance. I've never done something like this. It just sems very practical, since a 100% efficient antenna wouldnt introduce any heat. But , a 50% efficient one might produce about the same heat as a 50 watt light bulb. It would if the thermal mass of the antenna were the same as the light bulb, and if the thermal loss through the wiring were the same for the antenna as for the light bulb. But otherwise, they could be vastly different. I'd not declare this "ice box" to be a Lab Standard. But, if there was need, I'd sure try to evaluate the concept. When people like you cast doubt on anything I tink up, I begin to doubt myself. Jerry Well, then I've done a good service. Only when you have doubts about your methodolgy will you have any incentive to take the time to try and understand what you're doing. Any conclusions you reach about the antenna's efficiency (except that it's not 100% efficient - duh) will be completely worthless unless you get at least some kind of handle on the relationship between the heat and the temperature. Roy Lewallen, W7EL Roy Since I consider antenna efficiency difficult to measure accurately, I'd be willing to try to measure it as carefully as *practical*. If that required that the referance heater had a similar "thermal mass" to that of the antenna under test, I could probably make a heater that did have a thermal mass equivalent to that of the antenna. But, I would propose that there is no easier way to actually measure an antenna's efficiency than to measure the amount of power it turns into heat. Thats a statement I cant back up, and I know it. What is a better way to measure an antenna's efficiency?? |
Jerry Martes wrote:
Roy Since I consider antenna efficiency difficult to measure accurately, I'd be willing to try to measure it as carefully as *practical*. If that required that the referance heater had a similar "thermal mass" to that of the antenna under test, I could probably make a heater that did have a thermal mass equivalent to that of the antenna. But, I would propose that there is no easier way to actually measure an antenna's efficiency than to measure the amount of power it turns into heat. Thats a statement I cant back up, and I know it. What is a better way to measure an antenna's efficiency?? I believe it would usually be easier and more accurate to measure the amount of power it turns into radiation. That is, measure the strength of the radiated field compared with an antenna of known efficiency and preferably having a similar pattern. Neither is easy, and a method that's "practical" from your point of view might well yield results which are so grossly inaccurate as to be useless. But go ahead, do a careful estimate of the accuracy you expect, do some measurements of various simple antennas whose loss is easy to calculate and compare the measured results, and see how well you can do. It's probably within the reach of a very careful amateur to make measurements which are accurate enough to be useful. It just isn't easy, and requires knowing the relationship between heat and temperature, where the heat is going, sources of error and the amount they can contribute, and a whole lot of care and attention to detail. And that's to get even crudely accurate results. For myself, I'd model it as Reg suggests (although I'd use a program rather than the back of an envelope as he would) and easily believe that the model results are more accurate than any measurement I'd be able to make. However, neither calculation or measurement results are likely to alter the claims made by manufacturers of miracle antennas and their fans. Roy Lewallen, W7EL |
On Mon, 16 Aug 2004 23:25:20 GMT, "Jerry Martes"
wrote: What is a better way to measure an antenna's efficiency?? Hi Jerry, I see you are suffering from answers out to three decimals again. Your idea is not so far fetched, it is the simple calorimetric bomb. With enough patience and references, yes, you could measure inefficiency. However, the inefficiency could easily be lost in the inaccuracy and patience is not a virtue where simpler methods prevail. You rightly note that a total integration of all field strengths would be required, and be far more cumbersome. This is the classic treatment, but when done once with a reference for comparison, it is unnecessary to apply to other antennas of simple characteristics. Others note that simple comparisons serve quite suitably. For a small antenna (that is, in relation to wavelength such as the DLM and others like CFA/eh/fractals purport to operate efficiently in) there is no hint that the radiation lobes are going to offer manifestly high gain so as to drive comparisons off the chart. Certainly inventors make such fantasy claims, and those claims characteristically remain unsubstantiated. The DLM is a classic example. Side by side comparisons of the DLM with known good antennas, or even known poor ones with similar lobe patters could easily reveal efficiency. I suppose these same inventors could crow about a razor thin 24dB gain lobe pointed at the horizon (if you only knew the tune-up procedures), but you are not going to find this from any antenna packed into a box with less than quarterwave dimensions on all sides. [readers: Examples proving this last sentence wrong are welcome.] 73's Richard Clark, KB7QHC |
I sure disagree about being able to determine an antenna's efficiency by either resistance measurements or by measuring received signa;l strength at any one point in space. From practical, engineer's point of view, and we are looking at shortened (loaded) antennas, you (or at least I) want to know how efficient the loaded antenna is vs. equivalent (same pattern producing) antenna. You want to compare oranges with oranges. The ultimate indicator is how much is one better (worst) than the other producing more (less) transmit (or receive) signal. That is the ultimate parameter that we are looking for, that's what you want to measure and compare. We have dB as a unit for that. 3dB means you gain (lose) double (power) signal. If you lose 50% in the heat, you will see corresponding loss in signal strength. So forget the igloo! But, you are certainly a much smarter fuy than I ever was. So, I am not equipped to get into a news group contest. How did you arrive at that without putting me in the styrofoam igloo, or that I am Fuy? :-) It is my contention that the antenna under test's complete radiation pattern and field strength would have to be measured and integrated if field strength is used to determine it's efficiency. That could get coplicated. NOT! That's why you want to use the same pattern producing antennas for comparison (apples to apples) i.e. quarter wave (electrical) shortened (loaded) vertical vs. full size quarter wave vertical made of same material (tubing). You can make measurements at the same point (properly chosen) and compare signal levels while swapping the antennas at the same test site. It would have seemed to me that the loss in any "R" is dependent on the current flowing in it. And, I'd be concerned that any resonances could have higher circulating currents at the operating frequency. Circulating in what? If you can point out the errors in my convictions, I'd like to read about where I'm wrong. You can be "convicted" in anything you like. But you have to look at the problems and see what are you trying to achieve. I always try to make antenna to produce the maximum signal in the desired direction, pattern. That's what you try to measure, evaluate. Anything else is just contributing factor that gets included in the final parameter - signal strength. You can fart with heat, resistances, etc., I do not use antennas for heating, I use them for producing or extracting signals and that's what I am interested in and want to quantify. You need proper "standard" and use proper parameters to compare your "miracle" against. If Mr. Vincent "discovers" that his shortened antenna is more broadband than full size (same electrical length) radiator, than he has some serious resistors "broadening" the response. My dummy load is perfect broadband "antenna" and almost 100% "efficient" - turns almost 100% of power into a heat, but radiates almost nothing. The point is, you can measure other things like heat generated by the loses, but you are neglecting other parameters that come to play, leading you astray, while neglecting the most important parameter - the result you are (or I am) after - the signal strength! Does that "convict" you? Otherwise I rest my case. Jerry Yuri, K3BU.us |
"Roy Lewallen" wrote in message ... Jerry Martes wrote: Roy Since I consider antenna efficiency difficult to measure accurately, I'd be willing to try to measure it as carefully as *practical*. If that required that the referance heater had a similar "thermal mass" to that of the antenna under test, I could probably make a heater that did have a thermal mass equivalent to that of the antenna. But, I would propose that there is no easier way to actually measure an antenna's efficiency than to measure the amount of power it turns into heat. Thats a statement I cant back up, and I know it. What is a better way to measure an antenna's efficiency?? I believe it would usually be easier and more accurate to measure the amount of power it turns into radiation. That is, measure the strength of the radiated field compared with an antenna of known efficiency and preferably having a similar pattern. Neither is easy, and a method that's "practical" from your point of view might well yield results which are so grossly inaccurate as to be useless. But go ahead, do a careful estimate of the accuracy you expect, do some measurements of various simple antennas whose loss is easy to calculate and compare the measured results, and see how well you can do. It's probably within the reach of a very careful amateur to make measurements which are accurate enough to be useful. It just isn't easy, and requires knowing the relationship between heat and temperature, where the heat is going, sources of error and the amount they can contribute, and a whole lot of care and attention to detail. And that's to get even crudely accurate results. For myself, I'd model it as Reg suggests (although I'd use a program rather than the back of an envelope as he would) and easily believe that the model results are more accurate than any measurement I'd be able to make. However, neither calculation or measurement results are likely to alter the claims made by manufacturers of miracle antennas and their fans. Roy Lewallen, W7EL Roy If I had your credentials, I'd measure antenna efficiency the way you prescribe. It is only because I have no faith in my abiliuty to convince anyone what the pattern of a "New-Revolutionary is, that I'd get a thermometer out to chech my predictions that the antenna has *no* loss, like this guy does. As I read this thread, there is one guy who thinks measuring the temperature of an antenna for getting information on its efficiency. And all the other posts consider that guy to be 'on the wrong path'. I'd advise doing it some way *other than* measuring heat of the antenna. Jerry |
Yuri
I realize you are a smart and important guy who knows alot about electronucs. But, when you enter in a thread at this time with statements about defining "3 DB" I wonder if you think everyone else is supid except you. Whats the point of defining "3DB?? I used to work with some very good engineers who happened to think measuring measuring antenna heating was a fairly decent way of getting "loss" data on an antenna. I happen to think it is a good way to get some preliminary info on antenna loss. So, when you tell me to "forget the igloo", you seem to have placed yourself in a position where you think you know how to evaluate antenna efficiency and that I dont. I dont think you are *that* smart. Jerry "Yuri Blanarovich" wrote in message ... I sure disagree about being able to determine an antenna's efficiency by either resistance measurements or by measuring received signa;l strength at any one point in space. From practical, engineer's point of view, and we are looking at shortened (loaded) antennas, you (or at least I) want to know how efficient the loaded antenna is vs. equivalent (same pattern producing) antenna. You want to compare oranges with oranges. The ultimate indicator is how much is one better (worst) than the other producing more (less) transmit (or receive) signal. That is the ultimate parameter that we are looking for, that's what you want to measure and compare. We have dB as a unit for that. 3dB means you gain (lose) double (power) signal. If you lose 50% in the heat, you will see corresponding loss in signal strength. So forget the igloo! But, you are certainly a much smarter fuy than I ever was. So, I am not equipped to get into a news group contest. How did you arrive at that without putting me in the styrofoam igloo, or that I am Fuy? :-) It is my contention that the antenna under test's complete radiation pattern and field strength would have to be measured and integrated if field strength is used to determine it's efficiency. That could get coplicated. NOT! That's why you want to use the same pattern producing antennas for comparison (apples to apples) i.e. quarter wave (electrical) shortened (loaded) vertical vs. full size quarter wave vertical made of same material (tubing). You can make measurements at the same point (properly chosen) and compare signal levels while swapping the antennas at the same test site. It would have seemed to me that the loss in any "R" is dependent on the current flowing in it. And, I'd be concerned that any resonances could have higher circulating currents at the operating frequency. Circulating in what? If you can point out the errors in my convictions, I'd like to read about where I'm wrong. You can be "convicted" in anything you like. But you have to look at the problems and see what are you trying to achieve. I always try to make antenna to produce the maximum signal in the desired direction, pattern. That's what you try to measure, evaluate. Anything else is just contributing factor that gets included in the final parameter - signal strength. You can fart with heat, resistances, etc., I do not use antennas for heating, I use them for producing or extracting signals and that's what I am interested in and want to quantify. You need proper "standard" and use proper parameters to compare your "miracle" against. If Mr. Vincent "discovers" that his shortened antenna is more broadband than full size (same electrical length) radiator, than he has some serious resistors "broadening" the response. My dummy load is perfect broadband "antenna" and almost 100% "efficient" - turns almost 100% of power into a heat, but radiates almost nothing. The point is, you can measure other things like heat generated by the loses, but you are neglecting other parameters that come to play, leading you astray, while neglecting the most important parameter - the result you are (or I am) after - the signal strength! Does that "convict" you? Otherwise I rest my case. Jerry Yuri, K3BU.us |
On Mon, 16 Aug 2004 11:42:19 -0700, Roy Lewallen
wrote: It's not clear to me how you could get quantitative data from measurements in a styrofoam container. Let's say you put 100 watts into the antenna for five minutes and the temperature rise (of the coil? helical winding? air?) was 10 degrees C. How would you calculate the loss or efficiency from that information? First of all, the test should not be run for 5 minutes, but until a thermal equilibrium inside the container has been established, possibly mixing the air inside the container with a fan. This solves the thermal mass problems when equilibrium has been established. Measure the power fed to the antenna. The temperature outside of the container should remain stable during the test. Then the temperature difference across the container wall is known, as well as the wall surface area and thickness and hopefully also the thermal conductivity for styrofoam (from the manufacturer). Now the thermal resistance of the container as well as the temperature difference is known and the power dissipation can be calculated. This is very similar to calculating the heatsink requirements for transistors. If the thermal conductivity for the styrofoam is not known, run a predefined amount of power to the antenna until equilibrium has been reached and measure the temperature. Inside the container, disconnect the antenna, attach the feedline to a dummy load (possibly attaching it to some large metallic part of the antenna to act as a heatsink). Close the container and feed RF-power into the dummy load at an adjustable power level, until the same stable temperature is reached as with the actual antenna. Measure the power fed into the dummy load. This will eliminate the feedline conductivity problem as well as offset errors in the power meter (but not linearity errors). This way the power dissipated by the dummy load is the same as the power dissipated in the antenna losses in the first place and thus, the efficiency can be calculated. To avoid any power meter linearity problems, reconnect the antenna again, feed in the original full power and verify that there is a thermal equilibrium at the original temperature and outside temperature. Insert a calibrated step attenuator ahead of the power meter and adjust it until it reads the same value as in the dummy load test. You can then read directly from the step attenuator, how many dBs the total full transmitter power was compared to the dummy load power which is also the antenna thermal dissipation value. A 10 dB setting would indicate that the thermal losses are only 10 % of the total power or 90 % antenna efficiency, a 3 dB reading would indicate that half of the power is radiated and the other half is dissipated in the antenna, thus 50 % efficiency. However, you would need a step attenuator with 0.1 steps to measure the worst antennas :-). Paul OH3LWR |
So, when you tell me to "forget the igloo", you seem to have placed
yourself in a position where you think you know how to evaluate antenna efficiency and that I dont. I dont think you are *that* smart. Jerry You win, I ain't so smart as I thought. :-) I thought that antenna is supposed to radiate RF in the direction and with pattern one desires. That's what I want to measure, how effective radiator it is, how much RF it produces at the point of interest. If you want to know how well it works as a heater, more power to you. I am not in a ****ing contest who is "smarter", I was trying to convey some practicality and what I do and what I am interested in. Over and out! Back to DR1 (www.computeradio.us) Yuri, K3BU |
|
First of all, the test should not be run for 5 minutes, but until a
thermal equilibrium inside the container has been established, possibly mixing the air inside the container with a fan. This solves the thermal mass problems when equilibrium has been established. Measure the power fed to the antenna. The temperature outside of the container should remain stable during the test. Then the temperature difference across the container wall is known, as well as the wall surface area and thickness and hopefully also the thermal conductivity for styrofoam (from the manufacturer). Now the thermal resistance of the container as well as the temperature difference is known and the power dissipation can be calculated. This is very similar to calculating the heatsink requirements for transistors. If the thermal conductivity for the styrofoam is not known, run a predefined amount of power to the antenna until equilibrium has been reached and measure the temperature. Inside the container, disconnect the antenna, attach the feedline to a dummy load (possibly attaching it to some large metallic part of the antenna to act as a heatsink). Close the container and feed RF-power into the dummy load at an adjustable power level, until the same stable temperature is reached as with the actual antenna. Measure the power fed into the dummy load. This will eliminate the feedline conductivity problem as well as offset errors in the power meter (but not linearity errors). This way the power dissipated by the dummy load is the same as the power dissipated in the antenna losses in the first place and thus, the efficiency can be calculated. To avoid any power meter linearity problems, reconnect the antenna again, feed in the original full power and verify that there is a thermal equilibrium at the original temperature and outside temperature. Insert a calibrated step attenuator ahead of the power meter and adjust it until it reads the same value as in the dummy load test. You can then read directly from the step attenuator, how many dBs the total full transmitter power was compared to the dummy load power which is also the antenna thermal dissipation value. A 10 dB setting would indicate that the thermal losses are only 10 % of the total power or 90 % antenna efficiency, a 3 dB reading would indicate that half of the power is radiated and the other half is dissipated in the antenna, thus 50 % efficiency. However, you would need a step attenuator with 0.1 steps to measure the worst antennas :-). Paul OH3LWR Paul, simple approaches to calorimetry are, as you know, very difficult. Having done them extensively, I don't recommend radio amateurs try it, as the likelihood of missing even a second-order issue/factor is high. Knowledge of Netwon's equations is essential vis a vis heating and cooling rates and equilibrium. (again, you know this; others might not.) Since the DLM/DLD is a monochromatic antenna, it readily fits into a Wheeler cap approach for efficiency measurement. There was no data nor discussion of such an attempt in this veign. There are no valid efficiency measurements of the DLM from the data I saw. If someone sees otherwise, kindly let us know and enlighten us. 73, Chip N1IR .. |
On Tue, 17 Aug 2004 13:10:19 +0300, Paul Keinanen
wrote: First of all, the test should not be run for 5 minutes, but until a thermal equilibrium inside the container has been established, possibly mixing the air inside the container with a fan. Hi Paul, First, you show that this is not an intractable problem, merely one that requires care. Good work. However, as to the statement above, and the presumptions that follow, there is no equilibrium to observe as the test implementation has been described. You are pouring calories into an insulated environment which can only raise temperature without end (short of destruction, of course). As I described elsewhere, this is called a caloric bomb, and as such should be limited in time for all comparisons. What you are describing requires a steady flow of coolant through the chamber where you measure the inlet and exhaust temperatures and use THAT differential. Care must be given to not exhaust into the inlet, and to maintain the inlet with a body of constant temperature air (to simplify matters). The problem is not really that difficult - it only takes attention to detail such as your response indicates. 73's Richard Clark, KB7QHC |
On Tue, 17 Aug 2004 15:50:05 GMT, Richard Clark
wrote: However, as to the statement above, and the presumptions that follow, there is no equilibrium to observe as the test implementation has been described. You are pouring calories into an insulated environment which can only raise temperature without end (short of destruction, of course). As I described elsewhere, this is called a caloric bomb, and as such should be limited in time for all comparisons. You seem to assume that no thermal power will flow through the styrofoam walls of the box. Your statement is true if you insert a huge amount of power into the box, in which case the temperature would climb, until the styrofoam would melt. However, the measurement can be done at much lower power levels that are compatible with the thermal conductivity of the styrofoam. If styrofoam would be an ideal isolator, you could put some deep freeze food into a styrofoam box, move to your summer cottage and hope that the food would still be eatable after a week. Unfortunately this is not true :-(. When doing antenna efficiency measurements, the power levels should be set to a level, in which the temperature increase is manageable (below the melting point of the styrofoam). To give an example of the power levels required, assume that you insert a 1 kg (1 liter) bottle of drink at 0 C into the test container and after 10000 seconds (about 3 hours) the drink temperature is at +10 C, the energy needed is about 40 kJ, thus the leakage through the container walls would be about 4 W. With the outside temperature of 20 C, the average temperature difference would be 15 C and the thermal conductivity about 4 C/W. This is what you usually get with some power transistors with a heat sink :-). If you build an igloo around the "miracle" antenna, you should be able to measure the heat generated (and thus efficiency) with power levels well below the legal limit in most countries and with bad antennas 10-100 W should be enough. Of course, you should make sure that the styrofoam own RF dissipation is sufficiently small at the test frequency. Paul OH3LWR |
OH3LWR:
Of course that is what everyone would want to measure, but unless you are working in the millimeter bands in a non-echoic chamber, determining the true (absolute) radiation pattern can be quite problematic. We are looking at shortened, loaded verticals, monopoles. So you stick the "standard" - quarter wave radiator in the test point, measure it at proper point, then you replace it with "miracle" antenna and do the same, feeding them with the same power. The difference is in overall efficiency. Lets not lose sight of what are we talking about and what the real "problem" is. How do you build igloo for 4 square? Comon guys, this is old stuff, has been done for 100 years already. Lets not fly off on tangents. Is anyone out there who "calorimetered" the antenna? Yuri, K3BU |
Yes, the temperature will rise until the rate of heat leaving the
container equals the power (rate of energy) entering the box. As the interior of the box gets hotter (more exactly, as the inside-outside temperature differential increases), heat exiting the box will increase. So at some internal temperature an equilibrium will be reached. You'd want to use a power level high enough to make this temperature well above ambient so that small variations in ambient temperature won't badly skew the results, but low enough that you don't cook the box's innards. The method you propose seems workable, except I didn't see any mention of heat leaving the box via thermal conduction along the wires. Depending on the box's insulating property and the wires, this could be a significant contributor to the total heat loss from the box. Therefore it's very important to either insure that this loss is negligible compared to the loss through the styrofoam, or else to manage it (most easily by using exactly the same wires and wire orientation during calibration and test). As I mentioned earlier, it's probably within the means of an amateur to make useful measurements, but it would take a lot of care and attention to detail. There may well be other factors none of us have considered (as examples, the presence of variable drafts in the vicinity of the box, which could impact the heat transfer rate in a major way, or nonlinearity of convective cooling), so measurements of various bodies of known dissipation would have to be measured to confirm that all significant factors are accounted for before there will be any confidence in the results. Roy Lewallen, W7EL Paul Keinanen wrote: On Tue, 17 Aug 2004 15:50:05 GMT, Richard Clark wrote: However, as to the statement above, and the presumptions that follow, there is no equilibrium to observe as the test implementation has been described. You are pouring calories into an insulated environment which can only raise temperature without end (short of destruction, of course). As I described elsewhere, this is called a caloric bomb, and as such should be limited in time for all comparisons. You seem to assume that no thermal power will flow through the styrofoam walls of the box. Your statement is true if you insert a huge amount of power into the box, in which case the temperature would climb, until the styrofoam would melt. However, the measurement can be done at much lower power levels that are compatible with the thermal conductivity of the styrofoam. If styrofoam would be an ideal isolator, you could put some deep freeze food into a styrofoam box, move to your summer cottage and hope that the food would still be eatable after a week. Unfortunately this is not true :-(. When doing antenna efficiency measurements, the power levels should be set to a level, in which the temperature increase is manageable (below the melting point of the styrofoam). To give an example of the power levels required, assume that you insert a 1 kg (1 liter) bottle of drink at 0 C into the test container and after 10000 seconds (about 3 hours) the drink temperature is at +10 C, the energy needed is about 40 kJ, thus the leakage through the container walls would be about 4 W. With the outside temperature of 20 C, the average temperature difference would be 15 C and the thermal conductivity about 4 C/W. This is what you usually get with some power transistors with a heat sink :-). If you build an igloo around the "miracle" antenna, you should be able to measure the heat generated (and thus efficiency) with power levels well below the legal limit in most countries and with bad antennas 10-100 W should be enough. Of course, you should make sure that the styrofoam own RF dissipation is sufficiently small at the test frequency. Paul OH3LWR |
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