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New antenna
Gene Fuller wrote:
... The patent, US 7187335, is a real hoot. I especially like the part where he describes doubling the bandwidth by adding a parasitic winding intertwined with the base coil helix. Do you suppose his antenna is in equilibrium? Could proper application of Artsian-Gaussian theory improve it even more? 73, Gene W4SZ What? You don't see cutting the capacitance between winding turns as causing some measurable effect which in turn affects a property of the antenna proper? Thicker conductor(s) usually means a measurable gain in bandwith, with a parasitic element in such close proximity to the major element, a gain in bandwidth is not that difficult to propose and attempt to prove/disprove. Regards, JS |
#2
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New antenna
John Smith wrote:
Gene Fuller wrote: ... The patent, US 7187335, is a real hoot. I especially like the part where he describes doubling the bandwidth by adding a parasitic winding intertwined with the base coil helix. Do you suppose his antenna is in equilibrium? Could proper application of Artsian-Gaussian theory improve it even more? 73, Gene W4SZ What? You don't see cutting the capacitance between winding turns as causing some measurable effect which in turn affects a property of the antenna proper? Thicker conductor(s) usually means a measurable gain in bandwith, with a parasitic element in such close proximity to the major element, a gain in bandwidth is not that difficult to propose and attempt to prove/disprove. Regards, JS John, The effects you mention may have some impact on bandwidth, but they don't double it. And the capacitance probably increases, not decreases. Placing an extra conductor between two capacitor plates increases the capacitance. At the same time placing a grounded shield between two capacitor plates reduces or eliminates the coupling between the original plates. It is not clear to me which effect would dominate in this case. In either case it is unlikely to be very important. Lots of people understand how to make an antenna broadband; simply add resistance. This is not always "bad". It is merely a choice. Just for grins I did a little EZNEC experiment. I started with a base loaded monopole that used a generated helix as the loading coil. I adjusted and resonated the system to SWR = 1 and took a look at the bandwidth. I arbitrarily took SWR = 2 as the bandwidth limits. I then added a parasitic winding between the turns of the helix. This winding was not connected to anything. I reran the simulations. What I found was interesting, but not surprising. When the wires were treated as lossless, there was virtually no difference in bandwidth or any other parameter. The parasitic winding had essentially no impact. When I changed the wires to copper, the bandwidth increased in both cases. However, in the case with the parasitic winding the new bandwidth was 2.5 times as large as the case without the extra winding. The resonant input impedance was also about 2.5 times larger. There is only one plausible explanation for this observation. The parasitic winding adds loss to the antenna system. I won't claim this is "bad". Depends on the characteristics desired. The bottom line is that there is no wondrous invention here. Either Vincent knew about this effect and chose to ignore it, or he did not understand what was happening. The capacitance explanation is just baloney. 73, Gene W4SZ |
#3
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New antenna
Gene Fuller wrote:
... 73, Gene W4SZ Well, OK. Post your EZNEC modeling mockup of the antenna and we'll check it out ... :-) JS |
#4
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New antenna
Gene Fuller wrote:
. . . What I found was interesting, but not surprising. When the wires were treated as lossless, there was virtually no difference in bandwidth or any other parameter. The parasitic winding had essentially no impact. When I changed the wires to copper, the bandwidth increased in both cases. However, in the case with the parasitic winding the new bandwidth was 2.5 times as large as the case without the extra winding. The resonant input impedance was also about 2.5 times larger. There is only one plausible explanation for this observation. The parasitic winding adds loss to the antenna system. I won't claim this is "bad". Depends on the characteristics desired. You can easily verify this by noting the change in gain as the extra winding is added and deleted. You should also see a corresponding change in feedpoint resistance, assuming that the extra winding doesn't change the current distribution. A couple of additional interesting experiments would be: 1. Increase the loss of the coil in a model without the extra winding until the gain is the same as the model with copper loss and no extra winding. Then see how the bandwidth compares to the original model with extra winding. 2. Instead of increasing the loss of the coil, add a resistor to the base of the copper loss non-extra winding antenna and adjust it so the gain is the same as for the model with copper loss and extra winding. How does the bandwidth compare to the original model with the extra winding? The bottom line is that there is no wondrous invention here. Either Vincent knew about this effect and chose to ignore it, or he did not understand what was happening. The capacitance explanation is just baloney. I'm afraid that's probably true. With antennas, you can choose any two of efficient, and broadband, and electrically small. This antenna claims all three, so I'm very skeptical. Roy Lewallen, W7EL |
#5
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New antenna
On Oct 11, 4:25 pm, Roy Lewallen wrote:
Gene Fuller wrote: . . . What I found was interesting, but not surprising. When the wires were treated as lossless, there was virtually no difference in bandwidth or any other parameter. The parasitic winding had essentially no impact. When I changed the wires to copper, the bandwidth increased in both cases. However, in the case with the parasitic winding the new bandwidth was 2.5 times as large as the case without the extra winding. The resonant input impedance was also about 2.5 times larger. There is only one plausible explanation for this observation. The parasitic winding adds loss to the antenna system. I won't claim this is "bad". Depends on the characteristics desired. You can easily verify this by noting the change in gain as the extra winding is added and deleted. You should also see a corresponding change in feedpoint resistance, assuming that the extra winding doesn't change the current distribution. A couple of additional interesting experiments would be: 1. Increase the loss of the coil in a model without the extra winding until the gain is the same as the model with copper loss and no extra winding. Then see how the bandwidth compares to the original model with extra winding. 2. Instead of increasing the loss of the coil, add a resistor to the base of the copper loss non-extra winding antenna and adjust it so the gain is the same as for the model with copper loss and extra winding. How does the bandwidth compare to the original model with the extra winding? The bottom line is that there is no wondrous invention here. Either Vincent knew about this effect and chose to ignore it, or he did not understand what was happening. The capacitance explanation is just baloney. I'm afraid that's probably true. With antennas, you can choose any two of efficient, and broadband, and electrically small. This antenna claims all three, so I'm very skeptical. Roy Lewallen, W7EL- Hide quoted text - - Show quoted text - Maybe it not the wire but the insulation on the wire, A little dielectric heating would surely make it more broadbanded. Jimmie |
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