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Colinear antennas
On Tue, 15 Dec 2015 11:00:23 -0600, John S wrote:
On 12/15/2015 8:40 AM, Laszlo Lebrun wrote: Is it allowed to post here a question related to antennas and without crossposts? :-) Reading the content of the other threads, I'm not quite sure... OK let's try nevertheless: A colinear antenna is using alternating sections if coaxial cable whereas the signal is travelling half inside the coax, half outside. The length of the sections should be half wave considering the velocity factor of the used coaxial cable. I would tend to consider the velocity factor only for the parts of the antenna where the the signal is travelling *inside* the coax cable. I know, my reasoning is probably wrong, but why? Thank you for your advice Three collinear antenna blogs by a very knowledgeable ham: http://owenduffy.net/blog/?s=collinear Oh! I was not even completely wrong! One must really consider different velocities. The interactions are however symmetric, so it is not enough to make some sections shorter/ longer. The best way is to take high velocity coax to minimize the differences. -- Stand up against TTIP and ISDS ! |
#2
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Colinear antennas
On 12/15/2015 2:06 PM, Laszlo Lebrun wrote:
On Tue, 15 Dec 2015 11:00:23 -0600, John S wrote: On 12/15/2015 8:40 AM, Laszlo Lebrun wrote: Is it allowed to post here a question related to antennas and without crossposts? :-) Reading the content of the other threads, I'm not quite sure... OK let's try nevertheless: A colinear antenna is using alternating sections if coaxial cable whereas the signal is travelling half inside the coax, half outside. The length of the sections should be half wave considering the velocity factor of the used coaxial cable. I would tend to consider the velocity factor only for the parts of the antenna where the the signal is travelling *inside* the coax cable. I know, my reasoning is probably wrong, but why? Thank you for your advice Three collinear antenna blogs by a very knowledgeable ham: http://owenduffy.net/blog/?s=collinear Oh! I was not even completely wrong! One must really consider different velocities. The interactions are however symmetric, so it is not enough to make some sections shorter/ longer. The best way is to take high velocity coax to minimize the differences. Yup! That's the way I read it, too. Good luck. |
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