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A short 160M antenna - folded elements
On 11/8/2014 10:57 AM, Wayne wrote:
"John S" wrote in message ... On 11/7/2014 12:58 PM, wrote: wrote: snip The only downside to this antenna is that it is extremely narrow banded, only about a kHz or so. snip I realized I should expand on that. With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz. By staggering the values of the inductors in the four legs the bandwidth can be improved by a little bit. The best I could accomplish was about 1 Khz by making the leg values .96, .98, 1.02, and 1.04 times the central leg value. Going beyond a step factor of .02 made little difference in the bandwidth and the resonant frequency SWR started to increase. # Okay, but the starting target was to be able to feed a short antenna # with good efficiency and I think you hit that target. I know you want to # keep it as practical as possible, but I am impressed with your results. I agree. I like the approach. Anyone ready to tackle a fractal design :) I have no idea how to approach that, but I'm willing to read your posts on it. Start by assuming zero knowledge for me. |
A short 160M antenna - folded elements
On 11/8/2014 10:45 AM, wrote:
John S wrote: On 11/7/2014 12:58 PM, wrote: wrote: snip The only downside to this antenna is that it is extremely narrow banded, only about a kHz or so. snip I realized I should expand on that. With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz. By staggering the values of the inductors in the four legs the bandwidth can be improved by a little bit. The best I could accomplish was about 1 Khz by making the leg values .96, .98, 1.02, and 1.04 times the central leg value. Going beyond a step factor of .02 made little difference in the bandwidth and the resonant frequency SWR started to increase. Okay, but the starting target was to be able to feed a short antenna with good efficiency and I think you hit that target. I know you want to keep it as practical as possible, but I am impressed with your results. Thanks. The whole point of the exercise was to show there are way to overcome the generally low impedance of short antennas. Exactly! It was a challenge which has been shown to be surmountable by design. Feed losses become less of a burden this way. Do you think your results could be practical? Could ground resistance be used to widen the BW? I know, there are losses. But, maybe worth it? What do you think? |
A short 160M antenna - folded elements
On Saturday, November 8, 2014 11:15:33 AM UTC-6, John S wrote:
On 11/8/2014 10:57 AM, Wayne wrote: "John S" wrote in message ... On 11/7/2014 12:58 PM, wrote: wrote: snip The only downside to this antenna is that it is extremely narrow banded, only about a kHz or so. snip I realized I should expand on that. With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz. By staggering the values of the inductors in the four legs the bandwidth can be improved by a little bit. The best I could accomplish was about 1 Khz by making the leg values .96, .98, 1.02, and 1.04 times the central leg value. Going beyond a step factor of .02 made little difference in the bandwidth and the resonant frequency SWR started to increase. # Okay, but the starting target was to be able to feed a short antenna # with good efficiency and I think you hit that target. I know you want to # keep it as practical as possible, but I am impressed with your results. I agree. I like the approach. Anyone ready to tackle a fractal design :) And they say I like to stir it... lol I have no idea how to approach that, but I'm willing to read your posts on it. Start by assuming zero knowledge for me. We thrashed that around quite a bit many moons ago. Richard Clark in particular did quite a bit of pondering and puter simulation on the subject. http://www.qsl.net/kb7qhc/antenna/fractal/ I think the most chortle inducing moment was when a totally random design outdid one that the guru of all things fractal spit out using his highly self touted puter optimizations. I came to the conclusion that fractal antennas were nothing more than linear loading using pretty design schemes. Often no real advantage to a random design drawn with the eyes closed, but hey, if one can attract gov grants, contracts and such, using advanced forms of bafflegab to lure in the gullible, one can overlook such things while laughing all the way to the bank. :) Actually, I consider any symmetrical antenna design to be a fractal of sorts.. Even a dipole as the simplest form. |
A short 160M antenna - folded elements
John S wrote:
On 11/8/2014 10:45 AM, wrote: John S wrote: On 11/7/2014 12:58 PM, wrote: wrote: snip The only downside to this antenna is that it is extremely narrow banded, only about a kHz or so. snip I realized I should expand on that. With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz. By staggering the values of the inductors in the four legs the bandwidth can be improved by a little bit. The best I could accomplish was about 1 Khz by making the leg values .96, .98, 1.02, and 1.04 times the central leg value. Going beyond a step factor of .02 made little difference in the bandwidth and the resonant frequency SWR started to increase. Okay, but the starting target was to be able to feed a short antenna with good efficiency and I think you hit that target. I know you want to keep it as practical as possible, but I am impressed with your results. Thanks. The whole point of the exercise was to show there are way to overcome the generally low impedance of short antennas. Exactly! It was a challenge which has been shown to be surmountable by design. Feed losses become less of a burden this way. Do you think your results could be practical? Could ground resistance be used to widen the BW? I know, there are losses. But, maybe worth it? What do you think? I think if the goal is a practical antenna, the starting point should be how high can you practically go keeping in mind that a 1/4 wave 160M is on the order of 130 feet and in general the higher the greater the bandwidth and the less you have to be concerned with minimizing losses. In my urban lot, anything over about 30 feet becomes a problem. I do have a 33 foot tall vertical in the back yard with an autotuner at the base. It started out as just a 40M vertical. With the addition of the autotuner, it will tune and load 160 through 6 M. The performance on 6M is horrible as it is a cloud warmer at that frequency, but most of the other bands are OK or better. The 160 and 80 performance was poor, which I attibuted to losses in the tuner, so I put in a relay controlled high Q tapped coil to take some of the burden off of the autotuner on those bands. That helped quite a bit. I have been thinking about using the folded monopole technique to further improve things. That would require some more relays to switch the folded parts into the main radiator, essentially making it a fat radiator on other bands. The biggest issue is mechanical so until I figure out that part, I have left that project on the back burner for now. -- Jim Pennino |
A short 160M antenna - folded elements
"John S" wrote in message ... On 11/8/2014 10:57 AM, Wayne wrote: "John S" wrote in message ... On 11/7/2014 12:58 PM, wrote: wrote: snip The only downside to this antenna is that it is extremely narrow banded, only about a kHz or so. snip I realized I should expand on that. With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz. By staggering the values of the inductors in the four legs the bandwidth can be improved by a little bit. The best I could accomplish was about 1 Khz by making the leg values .96, .98, 1.02, and 1.04 times the central leg value. Going beyond a step factor of .02 made little difference in the bandwidth and the resonant frequency SWR started to increase. # Okay, but the starting target was to be able to feed a short antenna # with good efficiency and I think you hit that target. I know you want to # keep it as practical as possible, but I am impressed with your results. I agree. I like the approach. Anyone ready to tackle a fractal design :) # I have no idea how to approach that, but I'm willing to read your posts # on it. Start by assuming zero knowledge for me. That comment was made in jest, and nm5k picked up on it with his response. Some years back there were the Great Fractal Wars (TM) on this group. Some of the recent comments reminded me of those days. In summary, one poster was pushing his design of a fractal antenna and it took hundreds (if not thousands) of posts to get him to nail him down on the design. It didn't seem to have any particular advantage over other antennas, and had a more complex construction. |
A short 160M antenna - folded elements
Wayne wrote:
"John S" wrote in message ... On 11/8/2014 10:57 AM, Wayne wrote: "John S" wrote in message ... On 11/7/2014 12:58 PM, wrote: wrote: snip The only downside to this antenna is that it is extremely narrow banded, only about a kHz or so. snip I realized I should expand on that. With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz. By staggering the values of the inductors in the four legs the bandwidth can be improved by a little bit. The best I could accomplish was about 1 Khz by making the leg values .96, .98, 1.02, and 1.04 times the central leg value. Going beyond a step factor of .02 made little difference in the bandwidth and the resonant frequency SWR started to increase. # Okay, but the starting target was to be able to feed a short antenna # with good efficiency and I think you hit that target. I know you want to # keep it as practical as possible, but I am impressed with your results. I agree. I like the approach. Anyone ready to tackle a fractal design :) # I have no idea how to approach that, but I'm willing to read your posts # on it. Start by assuming zero knowledge for me. That comment was made in jest, and nm5k picked up on it with his response. Some years back there were the Great Fractal Wars (TM) on this group. Some of the recent comments reminded me of those days. In summary, one poster was pushing his design of a fractal antenna and it took hundreds (if not thousands) of posts to get him to nail him down on the design. It didn't seem to have any particular advantage over other antennas, and had a more complex construction. He also had some "antennas for hams" on his web site, long taken down, that he raved about. Apparently he thought he was the only one with any antenna analysis capability. -- Jim Pennino |
A short 160M antenna - folded elements
wrote in message ... Wayne wrote: "John S" wrote in message ... On 11/8/2014 10:57 AM, Wayne wrote: "John S" wrote in message ... On 11/7/2014 12:58 PM, wrote: wrote: snip The only downside to this antenna is that it is extremely narrow banded, only about a kHz or so. snip I realized I should expand on that. With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz. By staggering the values of the inductors in the four legs the bandwidth can be improved by a little bit. The best I could accomplish was about 1 Khz by making the leg values .96, .98, 1.02, and 1.04 times the central leg value. Going beyond a step factor of .02 made little difference in the bandwidth and the resonant frequency SWR started to increase. # Okay, but the starting target was to be able to feed a short antenna # with good efficiency and I think you hit that target. I know you want to # keep it as practical as possible, but I am impressed with your results. I agree. I like the approach. Anyone ready to tackle a fractal design :) # I have no idea how to approach that, but I'm willing to read your posts # on it. Start by assuming zero knowledge for me. That comment was made in jest, and nm5k picked up on it with his response. Some years back there were the Great Fractal Wars (TM) on this group. Some of the recent comments reminded me of those days. In summary, one poster was pushing his design of a fractal antenna and it took hundreds (if not thousands) of posts to get him to nail him down on the design. It didn't seem to have any particular advantage over other antennas, and had a more complex construction. # He also had some "antennas for hams" on his web site, long taken down, # that he raved about. # Apparently he thought he was the only one with any antenna analysis # capability. LOL...yeah, one time I took his "fractvert", which required two supports, and modified it to use one support. Then I posted the EZNEC results and he got real ****y about it. Good times? :) |
A short 160M antenna - folded elements
On Saturday, November 8, 2014 3:51:45 PM UTC-6, Wayne wrote:
LOL...yeah, one time I took his "fractvert", which required two supports, and modified it to use one support. Then I posted the EZNEC results and he got real ****y about it. Good times? :) What was the name of his sidekick? Phil I think it was? I once had him foaming at the mouth and drooling all over his keyboard. He was severely bent out of shape because I was heckling the Chipper over that antenna... chortle I'm a bad man I guess... lol |
A short 160M antenna - folded elements
wrote in message ... On Saturday, November 8, 2014 3:51:45 PM UTC-6, Wayne wrote: LOL...yeah, one time I took his "fractvert", which required two supports, and modified it to use one support. Then I posted the EZNEC results and he got real ****y about it. Good times? :) What was the name of his sidekick? Phil I think it was? I once had him foaming at the mouth and drooling all over his keyboard. He was severely bent out of shape because I was heckling the Chipper over that antenna... chortle I'm a bad man I guess... lol Yes, I think it was Phil. It's amusing to think back on those times, but don't think I'd like to repeat them :) |
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