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#1
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Could not get it to work. Below is my NEC2 code ( heavily segmented as it
is easier to figure out where to place the source and load). What am I doing wrong? Resonant on 7.25 MHz before extending the antenna. Approaches resonance on 22 MHz, when extended, with very high series L. A 40 m dipole is resonant on the 3rd harmonic anyway so all you are doing is isolating the extra 1/4 wave by placing a very high impedance at the quarter wave point. I guess I missed something, be interested in any comments. Regards, Frank Code: CM free space dipole antenna CE GW 1 99 -33 0 0 66 0 0 0.0026706 GS 0 0 .3048 GE 0 EX 0 1 33 0 1 0 LD 4 1 67 67 1200 0 LD 5 1 1 99 5.8001E7 FR 0 31 0 0 20 0.1 RP 0 181 1 1000 -90 90 1 1 EN "Cecil Moore" wrote in message ... The results of the measurement of current at the bottom and top of the coil in an off-center-fed dipole configuration should leave no room for doubt. ------1/4WL------FP------1/4WL------ Start out with a 1/2WL dipole. Measure the resonant fundamental frequency. Then, to one end, add a coil and another 1/4WL of wire ------1/4WL------FP------1/4WL------//////------1/4WL------ Adjust the coil inductance so the antenna is resonant on three times the fundamental frequency of the original dipole. Measure the current at the left(bottom) of the coil and measure the current at the right(top) of the coil. The current at the left of the coil will be nearly zero. The current at the right of the coil will be approximately the same as the feedpoint current, somewhere around 1-2 amps for 100w input. This can probably be demonstrated using the helix feature of EZNEC. -- 73, Cecil http://www.qsl.net/w5dxp "The current and voltage distributions on open-ended wire antennas are similar to the standing wave patterns on open-ended transmission lines ... Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents If and Ib ..." _Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489 ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
#2
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PS should I have used an actual helix? Very tedious to structure with code,
although have done it in other models. Noticed that the current in and out of the coil is vastly different when compared with using the lumped element model. Frank "Knarf" wrote in message news:Z4jfd.743$VA5.640@clgrps13... Could not get it to work. Below is my NEC2 code ( heavily segmented as it is easier to figure out where to place the source and load). What am I doing wrong? Resonant on 7.25 MHz before extending the antenna. Approaches resonance on 22 MHz, when extended, with very high series L. A 40 m dipole is resonant on the 3rd harmonic anyway so all you are doing is isolating the extra 1/4 wave by placing a very high impedance at the quarter wave point. I guess I missed something, be interested in any comments. Regards, Frank Code: CM free space dipole antenna CE GW 1 99 -33 0 0 66 0 0 0.0026706 GS 0 0 .3048 GE 0 EX 0 1 33 0 1 0 LD 4 1 67 67 1200 0 LD 5 1 1 99 5.8001E7 FR 0 31 0 0 20 0.1 RP 0 181 1 1000 -90 90 1 1 EN "Cecil Moore" wrote in message ... The results of the measurement of current at the bottom and top of the coil in an off-center-fed dipole configuration should leave no room for doubt. ------1/4WL------FP------1/4WL------ Start out with a 1/2WL dipole. Measure the resonant fundamental frequency. Then, to one end, add a coil and another 1/4WL of wire ------1/4WL------FP------1/4WL------//////------1/4WL------ Adjust the coil inductance so the antenna is resonant on three times the fundamental frequency of the original dipole. Measure the current at the left(bottom) of the coil and measure the current at the right(top) of the coil. The current at the left of the coil will be nearly zero. The current at the right of the coil will be approximately the same as the feedpoint current, somewhere around 1-2 amps for 100w input. This can probably be demonstrated using the helix feature of EZNEC. -- 73, Cecil http://www.qsl.net/w5dxp "The current and voltage distributions on open-ended wire antennas are similar to the standing wave patterns on open-ended transmission lines ... Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents If and Ib ..." _Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489 ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
#3
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Knarf wrote:
PS should I have used an actual helix? Very tedious to structure with code, although have done it in other models. Noticed that the current in and out of the coil is vastly different when compared with using the lumped element model. Yes, use an actual helix. If it will help, download octcoil2.ez from my web page by clicking he http://www.qsl.net/w5dxp/octcoil2.ez For this particular case: http://www.qsl.net/w5dxp/octcoil2.gif a lumped point inductance gives bogus results. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
#4
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Knarf wrote:
PS should I have used an actual helix? Very tedious to structure with code, although have done it in other models. Noticed that the current in and out of the coil is vastly different when compared with using the lumped element model. Most of the available implementations of NEC-2 include the ability to generate a helix. Look for information on a 'GH' command. Roy Lewallen, W7EL |
#5
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"Roy Lewallen" wrote in message ... Knarf wrote: PS should I have used an actual helix? Very tedious to structure with code, although have done it in other models. Noticed that the current in and out of the coil is vastly different when compared with using the lumped element model. Most of the available implementations of NEC-2 include the ability to generate a helix. Look for information on a 'GH' command. Roy Lewallen, W7EL Thanks for the info. Should have studied the NEC 2 manual more carefully. It is on page 20 with no card picture. Regards, Frank |
#6
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Roy Lewallen wrote:
Most of the available implementations of NEC-2 include the ability to generate a helix. Look for information on a 'GH' command. Some time ago, I generated an 8-sided coil for EZNEC 2.0. It was a lot easier than I thought at first. Here's one turn of dia=13" at about one turn per inch. Note 'y' always equals the x value from two lines up. x y z .5, .2, 4.00 .2, .5, 4.01 -.2, .5, 4.02 -.5, .2, 4.03 -.5, -.2, 4.04 -.2, -.5, 4.05 .2, -.5, 4.06 .5, -.2, 4.07 -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
#7
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"Cecil Moore" wrote in message ... Roy Lewallen wrote: Most of the available implementations of NEC-2 include the ability to generate a helix. Look for information on a 'GH' command. Some time ago, I generated an 8-sided coil for EZNEC 2.0. It was a lot easier than I thought at first. Here's one turn of dia=13" at about one turn per inch. Note 'y' always equals the x value from two lines up. x y z .5, .2, 4.00 .2, .5, 4.01 -.2, .5, 4.02 -.5, .2, 4.03 -.5, -.2, 4.04 -.2, -.5, 4.05 .2, -.5, 4.06 .5, -.2, 4.07 -- 73, Cecil http://www.qsl.net/w5dxp Your helix is far more elegant than my octagonal structure, where each turn is in the same plane, and a 90 deg segment then connects to the next turn. I have just experimented with the GH card -- combined with the GM card. It appears to be an excellent method of constructing a helix. I have not seriously attempted to determine the optimal segmentation, but as long as the segments are less than or equal to the turn spacing the results seem acceptable -- as with parallel transmission line models. I have also attempted to maintain the same segmentation on wires external to the helix, and to use the same wire size. While these structures are interesting, from the point of view of analyzing current distribution on an antenna, there seems to be very little difference in the actual performance of an antenna modeled with lumped element components. What I have learned (as mentioned in a previous posting) is that it is possible to predict, with a fair degree of accuracy, the actual inductance of a helix. 73, Frank |
#8
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Knarf wrote:
While these structures are interesting, from the point of view of analyzing current distribution on an antenna, there seems to be very little difference in the actual performance of an antenna modeled with lumped element components. Don't let the logical diversions throw you. The argument is, and always has been, about the current in a loading coil, not about the radiation pattern. The radiation pattern is absolutely irrelevant to the argument. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
#9
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Knarf wrote:
Could not get it to work. Below is my NEC2 code ( heavily segmented as it is easier to figure out where to place the source and load). What am I doing wrong? Resonant on 7.25 MHz before extending the antenna. Approaches resonance on 22 MHz, when extended, with very high series L. A 40 m dipole is resonant on the 3rd harmonic anyway so all you are doing is isolating the extra 1/4 wave by placing a very high impedance at the quarter wave point. I guess I missed something, be interested in any comments. The lumped point inductance will definitely not give the correct results. The coil needs to use the helix feature of EZNEC+ 4.0. I constructed an 8-sided coil out of segments in EZNEC 2.0 and the results can be viewed at: http://www.qsl.net/w5dxp/octcoil2.gif The dimensions and inductance are not perfect but the idea is perfectly clear. There's 0.11 amp at the bottom of the coil and 0.57 amps at the top of the coil. By playing with lengths of wire and frequency, I've seen the current at the bottom of the coil as low as 0.005 amps while the current at the top of the coil was about 0.6 amps. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
#10
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"Cecil Moore" wrote in message ... Knarf wrote: Could not get it to work. Below is my NEC2 code ( heavily segmented as it is easier to figure out where to place the source and load). What am I doing wrong? Resonant on 7.25 MHz before extending the antenna. Approaches resonance on 22 MHz, when extended, with very high series L. A 40 m dipole is resonant on the 3rd harmonic anyway so all you are doing is isolating the extra 1/4 wave by placing a very high impedance at the quarter wave point. I guess I missed something, be interested in any comments. The lumped point inductance will definitely not give the correct results. The coil needs to use the helix feature of EZNEC+ 4.0. I constructed an 8-sided coil out of segments in EZNEC 2.0 and the results can be viewed at: http://www.qsl.net/w5dxp/octcoil2.gif The dimensions and inductance are not perfect but the idea is perfectly clear. There's 0.11 amp at the bottom of the coil and 0.57 amps at the top of the coil. By playing with lengths of wire and frequency, I've seen the current at the bottom of the coil as low as 0.005 amps while the current at the top of the coil was about 0.6 amps. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Sorry that was really dumb, did not think before I posted the response. I was certainly aware that the currents in, and out, of a lumped element inductor are the same. I had recently modeled a short monopole with a physical, octagonal, helix (Now I learn about the GH card!). The difference between the lumped element and distributed inductor is significant, although the gains are almost identical from both models. 73, Frank |
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