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#1
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On Fri, 28 Oct 2005 20:37:07 GMT, Ron wrote:
Assume an incoming rf signal has exactly the same strength in all 3 dimensions i.e., completely omnidirectional. Question: would an antenna having gain capture any more signal power than a completely omnidirectional antenna with no gain? Hi All, Well, it is time to discard the speculation and let modeling approach this for an answer that at least offers more than swag. First we strip away the sphere and solve this in two dimensions. To do that we simply construct a ring of sources surrounding the prospective antennas and let the winning design emerge. EZNEC+ ver. 4.0 Dipole in Ring of Sources 11/2/2005 10:00:48 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 4.783 V. at 23.52 deg. Current = 0.06643 A. at 23.52 deg. Impedance = 72 + J 0 ohms Power = 0.3177 watts Total applied power = 2000 watts Total load power = 0.3177 watts Total load loss = 0.001 dB EZNEC+ ver. 4.0 Vert Yagi in Ring of Sources 11/2/2005 10:21:32 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 1.418 V. at 25.9 deg. Current = 0.1182 A. at 25.9 deg. Impedance = 12 + J 0 ohms Power = 0.1676 watts Total applied power = 2000 watts Total load power = 0.1676 watts Total load loss = 0.0 dB As the Bard would offer, there's many a slip between the cup and the lip. For a first pass approximation, and for all the potential for errors (which can now be routed out instead of gummed to death), it appears that the low gain (directivity) dipole absorbs more power than the high gain (directivity) yagi. 73's Richard Clark, KB7QHC |
#2
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Richard Clark wrote:
On Fri, 28 Oct 2005 20:37:07 GMT, Ron wrote: Assume an incoming rf signal has exactly the same strength in all 3 dimensions i.e., completely omnidirectional. Question: would an antenna having gain capture any more signal power than a completely omnidirectional antenna with no gain? Hi All, Well, it is time to discard the speculation and let modeling approach this for an answer that at least offers more than swag. First we strip away the sphere and solve this in two dimensions. To do that we simply construct a ring of sources surrounding the prospective antennas and let the winning design emerge. EZNEC+ ver. 4.0 Dipole in Ring of Sources 11/2/2005 10:00:48 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 4.783 V. at 23.52 deg. Current = 0.06643 A. at 23.52 deg. Impedance = 72 + J 0 ohms Power = 0.3177 watts Total applied power = 2000 watts Total load power = 0.3177 watts Total load loss = 0.001 dB EZNEC+ ver. 4.0 Vert Yagi in Ring of Sources 11/2/2005 10:21:32 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 1.418 V. at 25.9 deg. Current = 0.1182 A. at 25.9 deg. Impedance = 12 + J 0 ohms Power = 0.1676 watts Total applied power = 2000 watts Total load power = 0.1676 watts Total load loss = 0.0 dB As the Bard would offer, there's many a slip between the cup and the lip. For a first pass approximation, and for all the potential for errors (which can now be routed out instead of gummed to death), it appears that the low gain (directivity) dipole absorbs more power than the high gain (directivity) yagi. 73's Richard Clark, KB7QHC Hi Richard, What is the plane of polarization of the ring of sources, and what is the orientation of the dipole? 73, ac6xg |
#3
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On Thu, 03 Nov 2005 11:47:21 -0800, Jim Kelley
wrote: What is the plane of polarization of the ring of sources, and what is the orientation of the dipole? Hi Jim, Vertical in free space (which, of course, has no direction, but we know what Vertical implies). This also includes the yagi. 73's Richard Clark, KB7QHC |
#4
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![]() Richard Clark wrote: On Thu, 03 Nov 2005 11:47:21 -0800, Jim Kelley wrote: What is the plane of polarization of the ring of sources, and what is the orientation of the dipole? Hi Jim, Vertical in free space (which, of course, has no direction, but we know what Vertical implies). This also includes the yagi. If you wouldn't mind, try moving your Yagi a half wave forward or reverse. ac6xg |
#5
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On Thu, 03 Nov 2005 13:44:47 -0800, Jim Kelley
wrote: If you wouldn't mind, try moving your Yagi a half wave forward or reverse. Moving back one half wave: EZNEC+ ver. 4.0 Vert Yagi in Ring of Sources 11/3/2005 2:37:02 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 1.655 V. at -135.94 deg. Current = 0.1379 A. at -135.94 deg. Impedance = 12 + J 0 ohms Power = 0.2283 watts Total applied power = 2000 watts Total load power = 0.2283 watts Total load loss = 0.0 dB moving it such that its "driven" element is dead center to all radiators (original configuration had the reflector in dead center): EZNEC+ ver. 4.0 Vert Yagi in Ring of Sources 11/3/2005 2:40:58 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 1.584 V. at -22.13 deg. Current = 0.132 A. at -22.13 deg. Impedance = 12 + J 0 ohms Power = 0.2091 watts Total applied power = 2000 watts Total load power = 0.2091 watts Total load loss = 0.0 dB 73's Richard Clark, KB7QHC |
#6
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![]() Richard Clark wrote: On Thu, 03 Nov 2005 13:44:47 -0800, Jim Kelley wrote: If you wouldn't mind, try moving your Yagi a half wave forward or reverse. Moving back one half wave: EZNEC+ ver. 4.0 Vert Yagi in Ring of Sources 11/3/2005 2:37:02 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 1.655 V. at -135.94 deg. Current = 0.1379 A. at -135.94 deg. Impedance = 12 + J 0 ohms Power = 0.2283 watts Total applied power = 2000 watts Total load power = 0.2283 watts Total load loss = 0.0 dB moving it such that its "driven" element is dead center to all radiators (original configuration had the reflector in dead center): EZNEC+ ver. 4.0 Vert Yagi in Ring of Sources 11/3/2005 2:40:58 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 1.584 V. at -22.13 deg. Current = 0.132 A. at -22.13 deg. Impedance = 12 + J 0 ohms Power = 0.2091 watts Total applied power = 2000 watts Total load power = 0.2091 watts Total load loss = 0.0 dB 73's Richard Clark, KB7QHC It looks like you'd have to use an array of non-coherent sources in order to get rid of the phase cancellation effects (and really see what's going on). Thanks Richard. ac6xg |
#7
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On Thu, 03 Nov 2005 15:13:53 -0800, Jim Kelley
wrote: It looks like you'd have to use an array of non-coherent sources in order to get rid of the phase cancellation effects (and really see what's going on). Hi Jim, Then it would be answering a different problem. 73's Richard Clark, KB7QHC |
#8
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On Thu, 03 Nov 2005 15:13:53 -0800, Jim Kelley
wrote: use an array of non-coherent sources EZNEC+ ver. 4.0 Dipole in Ring of Rnd Sources 11/3/2005 5:39:03 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 0.002611 V. at -33.23 deg. Current = 3.627E-05 A. at -33.23 deg. Impedance = 72 + J 0 ohms Power = 9.47E-08 watts Total applied power = 1364 watts Total load power = 9.47E-08 watts Total load loss = 0.0 dB then moved quarterwave: EZNEC+ ver. 4.0 Dipole in Ring of Rnd Sources 11/3/2005 5:41:17 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 0.00676 V. at -110.1 deg. Current = 9.389E-05 A. at -110.1 deg. Impedance = 72 + J 0 ohms Power = 6.348E-07 watts Total applied power = 1364 watts Total load power = 6.348E-07 watts Total load loss = 0.0 dB then moved backwards a quarterwave EZNEC+ ver. 4.0 Dipole in Ring of Rnd Sources 11/3/2005 5:44:52 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 0.004604 V. at 29.97 deg. Current = 6.395E-05 A. at 29.97 deg. Impedance = 72 + J 0 ohms Power = 2.944E-07 watts Total applied power = 1364 watts Total load power = 2.944E-07 watts Total load loss = 0.0 dB EZNEC+ ver. 4.0 Yagi in Ring of Rnd Sources 11/3/2005 5:48:14 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 0.07004 V. at 66.62 deg. Current = 0.005837 A. at 66.62 deg. Impedance = 12 + J 0 ohms Power = 0.0004088 watts Total applied power = 1364 watts Total load power = 0.0004088 watts Total load loss = 0.0 dB moved back halfwave: EZNEC+ ver. 4.0 Yagi in Ring of Rnd Sources 11/3/2005 5:51:43 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 0.09133 V. at -53.63 deg. Current = 0.007611 A. at -53.63 deg. Impedance = 12 + J 0 ohms Power = 0.0006952 watts Total applied power = 1364 watts Total load power = 0.0006952 watts Total load loss = 0.0 dB (and really see what's going on) Hmmm, at least 1000 times more response... so what's going on? (aside from a possibly poor implementation of random). Trying to refine the sources table with tighter random assignments is positively brutal under EZNEC's primitive (read no) handling of columnar data. 73's Richard Clark, KB7QHC |
#9
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On Wed, 02 Nov 2005 22:27:45 -0800, Richard Clark
wrote: On Fri, 28 Oct 2005 20:37:07 GMT, Ron wrote: Assume an incoming rf signal has exactly the same strength in all 3 dimensions i.e., completely omnidirectional. Question: would an antenna having gain capture any more signal power than a completely omnidirectional antenna with no gain? Hi All, Well, it is time to discard the speculation and let modeling approach this for an answer that at least offers more than swag. First we strip away the sphere and solve this in two dimensions. To do that we simply construct a ring of sources surrounding the prospective antennas and let the winning design emerge. EZNEC+ ver. 4.0 Dipole in Ring of Sources 11/2/2005 10:00:48 PM --------------- LOAD DATA --------------- Frequency = 70 MHz Load 1 Voltage = 4.783 V. at 23.52 deg. Current = 0.06643 A. at 23.52 deg. Impedance = 72 + J 0 ohms Power = 0.3177 watts Total applied power = 2000 watts Total load power = 0.3177 watts Taking the determination above as the "standard" I then have progressed to place an NBS yagi in three space about the center to obtain its best result. All such expressions (x,y,z) of the placement of the NBS yagi are with respect to its "driven" element. 0,0,0 Power = 0.2091 watts ..5,0,0 Power = 0.2198 watts 1,0,0 Power = 0.1429 watts 1.5,0,0 Power = 0.1026 watts 2,0,0 Power = 0.1601 watts 2.5,0,0 Power = 0.2113 watts 3,0,0 Power = 0.1571 watts 3.5,0,0 Power = 0.06028 watts 4,0,0 Power = 0.04128 watts So, within one quadrant, and over the space of roughly a wavelength, and at intervals of roughly one eighth wavelength, nothing emerges as being equal to the "standard" above. Except perhaps a hidden peak between 0,0,0 and .5,0,0. To investigate this: ..25,0,0 Power = 0.2286 watts examining further: ..125,0,0 Power = 0.2219 watts nope, examining further: ..375,0,0 Power = 0.2278 watts nope, examining further: ..30,0,0 Power = 0.2291 watts nope, examining further: ..35,0,0 Power = 0.2285 watts nope, looks like the one before at .30,0,0 is the new sweet spot. Now, to proceed to investigate the other quadrants to see if there is symmetry: -3.5,0,0 Power = 0.03997 watts 0,3.5,0 Power = 0.005925 watts 0,-3.5,0 Power = 0.005859 watts This last offers that on the Y axis there is a strong symmetry, and along the X axis there is a moderate symmetry. Now, in regard to both the X and the Y axis, there is a moderate symmetry. If we were to look at the fine data attempting to find the peak, we should notice that the "center" of the antenna lies between the "driven" element and its reflector. My having chosen the "driven" element as the nominal center was in error and my guess is that if I re-visited the same quadrant test above, with that new center at the sweet spot, then we would find very strong symmetry in all four quadrants. I will add that the Y axis data supports this due to its strong symmetry that is relatively immune from the choice of antenna center - at least at this scale. Putting that aside, it is enough to suggest that barring an exquisitely positioned peak of rather a sharp rise, then the yagi exhibits a poorer response compared to a dipole of approx. 1.4dB. Others are encouraged to investigate further to reclaim that missing dB or to put the horns to my error. 73's Richard Clark, KB7QHC |
#10
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Richard Clark wrote:
Others are encouraged to investigate further to reclaim that missing dB or to put the horns to my error. Of course, you have deviated considerably from the original infinite number of coherent sources. -- 73, Cecil http://www.qsl.net/w5dxp |
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