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#1
November 22nd 14, 04:19 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
A special purpose antenna for maybe just below the 6M band. For railroad
cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. |
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#2
November 22nd 14, 04:38 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
"John S" wrote in message
... A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. Sounds like a (much) larger version of the antenna in your mobile phone |
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#3
November 22nd 14, 05:00 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
"John S" wrote in message ... A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. This sounds like a straightened out version of the DDRR antenna. QST did an article on it some years ago, but used some substandard construction techniques. It can be built for HF. It is essentially a quarter wave vertical bent over. The bent part can be straight or formed into a circle. IIRC the configuration you describe was used for presidential communications during the 1950s and was attached to campaign trains. The antenna also has a history on naval vessels. Some hams have used it as a means of having a HF vertical shorter than their fence to avoid homeowner association rules. I built a 2 meter version of the antenna in the 1970s. The antenna was constructed from 1/4 inch copper tubing formed into a ring, with the grounded straight vertical section being 2 inches long. It was tuned to resonance with a 1/2 inch disk attached to the open end. A screw moved the disk to form a variable capacitor. The antenna worked very well with local repeaters, and it allowed my Chevy van to have a top mounted antenna and still fit in the garage. |
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#4
November 22nd 14, 05:24 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
On 11/22/2014 12:00 PM, Wayne wrote:
"John S" wrote in message ... A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. This sounds like a straightened out version of the DDRR antenna. QST did an article on it some years ago, but used some substandard construction techniques. It can be built for HF. It is essentially a quarter wave vertical bent over. The bent part can be straight or formed into a circle. IIRC the configuration you describe was used for presidential communications during the 1950s and was attached to campaign trains. The antenna also has a history on naval vessels. Some hams have used it as a means of having a HF vertical shorter than their fence to avoid homeowner association rules. I built a 2 meter version of the antenna in the 1970s. The antenna was constructed from 1/4 inch copper tubing formed into a ring, with the grounded straight vertical section being 2 inches long. It was tuned to resonance with a 1/2 inch disk attached to the open end. A screw moved the disk to form a variable capacitor. The antenna worked very well with local repeaters, and it allowed my Chevy van to have a top mounted antenna and still fit in the garage. Sounds like a Saturn 6M halo antenna from the 60's. I never had one, but I knew a couple of guys who did. They thought the antenna was great. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
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#5
November 22nd 14, 05:43 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
On Sat, 22 Nov 2014 10:19:36 -0600, John S
wrote: A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. It's called a PIFA antenna. http://www.qsl.net/va3iul/Antenna/PIFA/PIFA_Planar_Inverted_F_Antenna.pdf http://www.antenna-theory.com/antennas/patches/pifa.php etc... They come in a wide variety of mutations, including one which you've described. They can also be designed using a slot instead of a wire. Most commonly, they're found on 2.4Ghz laptop antennas, aircraft antennas, low profile bus/railroad/taxi antennas, etc. Some random examples: https://www.tessco.com/products/displayProductInfo.do?sku=309440 https://www.tessco.com/products/displayProductInfo.do?sku=72370 http://www.sti-co.com/antenna-products/low-profile-antennas/rugged-aluminum -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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#6
November 22nd 14, 06:42 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
"Jerry Stuckle" wrote in message ... On 11/22/2014 12:00 PM, Wayne wrote: "John S" wrote in message ... A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. This sounds like a straightened out version of the DDRR antenna. QST did an article on it some years ago, but used some substandard construction techniques. It can be built for HF. It is essentially a quarter wave vertical bent over. The bent part can be straight or formed into a circle. IIRC the configuration you describe was used for presidential communications during the 1950s and was attached to campaign trains. The antenna also has a history on naval vessels. Some hams have used it as a means of having a HF vertical shorter than their fence to avoid homeowner association rules. I built a 2 meter version of the antenna in the 1970s. The antenna was constructed from 1/4 inch copper tubing formed into a ring, with the grounded straight vertical section being 2 inches long. It was tuned to resonance with a 1/2 inch disk attached to the open end. A screw moved the disk to form a variable capacitor. The antenna worked very well with local repeaters, and it allowed my Chevy van to have a top mounted antenna and still fit in the garage. # Sounds like a Saturn 6M halo antenna from the 60's. I never had one, # but I knew a couple of guys who did. They thought the antenna was great. My understanding of the halo is that it is a half wave dipole formed into a circle. The antenna I described is essentially a 1/4 wave vertical bent over with the bent portion parallel to the ground. My 2 meter version could be described as a 19 inch long vertical, bent over two inches from the ground, and the remaining 17 inches formed into a circle parallel to the ground. So the antenna only added 2 inches to the height of my van. |
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#7
November 22nd 14, 07:30 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
On 11/22/2014 10:19 AM, John S wrote:
A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. No, Guys, nothing that I have read so far is the thing I have in mind. Picture this... A folded unipole on a large sheet of conductive material. Let one of the vertical elements be connected to the sheet. The other is insulated from the sheet and has the generator attached. Now, this configuration has a high feed impedance, even when resonant. However, if you now bend the antenna at an appropriate point vertically so that the top portion leans horizontally to the sheet, the antenna gets lower to the sheet and the impedance lowers. I have an EZNEC file that I can share if anyone is interested. I will also continue to search my books for the example. |
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#8
November 22nd 14, 08:52 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
On 11/22/2014 1:42 PM, Wayne wrote:
"Jerry Stuckle" wrote in message ... On 11/22/2014 12:00 PM, Wayne wrote: "John S" wrote in message ... A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. This sounds like a straightened out version of the DDRR antenna. QST did an article on it some years ago, but used some substandard construction techniques. It can be built for HF. It is essentially a quarter wave vertical bent over. The bent part can be straight or formed into a circle. IIRC the configuration you describe was used for presidential communications during the 1950s and was attached to campaign trains. The antenna also has a history on naval vessels. Some hams have used it as a means of having a HF vertical shorter than their fence to avoid homeowner association rules. I built a 2 meter version of the antenna in the 1970s. The antenna was constructed from 1/4 inch copper tubing formed into a ring, with the grounded straight vertical section being 2 inches long. It was tuned to resonance with a 1/2 inch disk attached to the open end. A screw moved the disk to form a variable capacitor. The antenna worked very well with local repeaters, and it allowed my Chevy van to have a top mounted antenna and still fit in the garage. # Sounds like a Saturn 6M halo antenna from the 60's. I never had one, # but I knew a couple of guys who did. They thought the antenna was great. My understanding of the halo is that it is a half wave dipole formed into a circle. That could be; I don't remember a lot of details about it. But from what I remember about them, it was a pretty small circle for 1/2 wavelength on 6 meters. That would be around 3 meters in circumference, or slightly less than a meter in diameter. They weren't anywhere near that big. The antenna I described is essentially a 1/4 wave vertical bent over with the bent portion parallel to the ground. My 2 meter version could be described as a 19 inch long vertical, bent over two inches from the ground, and the remaining 17 inches formed into a circle parallel to the ground. So the antenna only added 2 inches to the height of my van. Sounds good; it still sounds close to a halo, IIRC. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
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#9
November 22nd 14, 10:09 PM
posted to rec.radio.amateur.antenna
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Interesting bent folded unipole antenna
"John S" wrote in message ... On 11/22/2014 10:19 AM, John S wrote: A special purpose antenna for maybe just below the 6M band. For railroad cars (a large metal ground plane). The antenna must be short enough to pass through tunnels and have a 50 ohm feed impedance. I saw this antenna in a book but I can no longer remember which book and, although I've searched, I can't seem to find a reference. It was probably from the 1950's. Anyway... Imagine a folded unipole over a large sheet of metal. It will probably have a high feed resistance of 100 or so ohms. But, if it is bent over 90 degrees starting a short distance above the ground plane, it can be adjusted to match a 50 ohm feed and with no imaginary component. This will satisfy not only the feed impedance but also the short height requirement. Other than the really nice ground plane of a railroad car's roof and using a frequency proportional to the plane, there is no obvious reason this cannot be use in other situations. Is that not really cool? Comments welcome, of course. # No, Guys, nothing that I have read so far is the thing I have in mind. # Picture this... # A folded unipole on a large sheet of conductive material. Let one of the # vertical elements be connected to the sheet. The other is insulated from # the sheet and has the generator attached. # Now, this configuration has a high feed impedance, even when resonant. # However, if you now bend the antenna at an appropriate point vertically # so that the top portion leans horizontally to the sheet, the antenna # gets lower to the sheet and the impedance lowers. # I have an EZNEC file that I can share if anyone is interested. I will # also continue to search my books for the example. Ahhh....the "folded" part didn't sink in when I responded. I suspect my original comments still apply. With two conductors, the current is half in each conductor, thus a doubling of radiation resistance at the feed point in one conductor. So by carefully selecting the height at which the vertical part is bent, there might be a good match for coax. I'll play with that configuration a bit on EZNEC. |
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#10
November 22nd 14, 10:11 PM
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Interesting bent folded unipole antenna
Wayne wrote:
snip My understanding of the halo is that it is a half wave dipole formed into a circle. Correct: http://en.wikipedia.org/wiki/Halo_antenna -- Jim Pennino |
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