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3 antennas modeled with EZNEC
Thanks to Wes, n7ws, I found out how easy it is to model a helical coil
with EZNEC. The following three antennas were modeled using the same coil, 4.5 turns, 12 inch diameter, 10.8 inches long, using approximately 14 feet of wire. The antennas are similar. The frequencies are different to illustrate three different arguments. EZNEC zero-impedance loads were placed directly below and directly above the coil to ascertain the currents. The accompanying .ez files can be downloaded and run on EZNEC if desired. 1. The first antenna is a simple center-loaded 1/4WL monopole. The lengths of wire above and below the coil are approximately the same as the length of wire used in the coil. This one illustrates the current taper through the loading coil. Calculations indicate that the coil occupies approximately 20% of the electrical length of the antenna. http://www.qsl.net/w5dxp/octcoil1.gif http://www.qsl.net/w5dxp/octcoil1.ez 2. The second antenna is electrically 3/4 wavelength long. This one illustrates how the current at the top of the loading coil can be greater than the current at the bottom of the loading coil. http://www.qsl.net/w5dxp/octcoil2.gif http://www.qsl.net/w5dxp/octcoil2.ez 3. The third antenna illustrates the phase-reversing coil described by Kraus in _Antennas_For_All_Applications_, 3rd edition. It is similar in concept to the Diamond NR72B when used on 70 cm. The current at the bottom of the coil is 180 degrees different in phase from the current at the top of the coil which means - for 1/2 of the RF cycle, current is flowing into both ends of the coil at the same time. For the other 1/2 cycle, current is flowing out of both ends of the coil at the same time. http://www.qsl.net/w5dxp/octcoil3.gif http://www.qsl.net/w5dxp/octcoil3.ez It appears to me that EZNEC handles the segmented wire coils in a manner related to the real world. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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