[LakelandARC] My Feedline Tunes My Antenna - Goodman [1 Attachment]

[Don Jeerings]

On 11/10/2015 08:27 AM, matthew at mrstevens.net [LakelandARC] wrote:
> [Attachment(s) <#TopText> from matthew at mrstevens.net [LakelandARC] 
> included below]
>
> This article is a reprint of a 1956 article that appeared in the 
> November 1991 QST. It might be old news to many of you, but it was 
> very helpful to me when I was trying to troubleshoot some 'odd' 
> problems with an antenna that I had put together. All the literature 
> that I had read while working on the project seemed to tell me how to 
> make the antenna, but not to much about why it worked. This is the one 
> that finally made it 'click' for me...maybe you just have to find 
> someone to explain things to you the right way.
>
> I think it would be great to spread the word about any other articles 
> or resources that any of you might have run across and found helpful. 
> If you have anything that you'd like to share with the club, please 
> let me know, email to KK4FEM(at)arrl.net. Since we are an ARRL 
> affiliate club, we are able to put the full text of any QST articles 
> (new or old) on our website, blog, yahoo group, etc., as long as it is 
> properly attributed to the source.
>
> Especially for newer hams (like me) I think this would be helpful 
> towards the dual goals of the
> "Continuation and extension of the amateur's proven ability to 
> contribute to the advancement of the radio art"
> and "[Expanding] the existing reservoir within the amateur radio 
> service of trained operators, technicians, and electronics experts." 
> (Part 97.1)
>
> Particularly the /electronics experts/ part :-)
>
> So, please, if anyone has any useful information that you have found, 
> just send it to me at KK4FEM(at)arrl.net, and we will put it on the 
> blog and in the "files" section on the yahoo group. That way we can 
> all learn, and keep learning from our experiences.
>
>
> -- 
> Matthew Stevens
> KK4FEM
>
>
> 
Matthew: I don't know what math level you are at, but in a (*resonate*) 
feed line, the voltages and currents (are not in phase with each 
other).  If you are familiar with complex numbers, it is easier to 
understand.


The conditions at any point in the feed line can be expressed a R +- JX  
Vector number. R is the resistive component and JX is the reactive 
component (a Vector Quantity)


This may sound very complicated, but once you understand it, it becomes 
simple and is the main tool for all antenna impedance matching 
calculations.


Every transmission line has a characteristic impedance (determined by 
the spacing and the material (air or plastic) separating the wires. When 
the impedance's are perfectly matched, the feed line becomes resistive 
only regardless of the length. ie Maximum power transfer.


To conclude, If you matching is *correct*, you have a *non-resonate 
(flat)* line that appears resistive, and It make no difference how long 
you feed line is.


If your matching is in-correct, your feed line becomes part of the 
radiating antenna, and the length is extremely critical.


Don  KI4EFL


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